Showing papers in "Behaviour in 1983"

Why Are Diurnal Primates Living in Groups

Abstract: There are two main competing theories on the evolution of group living in diurnal nonhuman primates. The first theory claims that predation avoidance favours group living, whereas there are only disadvantages to feeding in a group and feeding competition increases with group size. The second theory claims that there is a feeding advantage to group living deriving from communal defence of high-quality food patches and that predation is not important. These theories have not yet been rigorously tested. In this paper a critical test is proposed: the theories differ in the predicted relationship between a female's birth rate and the size of the group in which she lives (Fig. 1). An additional test is concerned with the predicted relationship between population density relative to food availability and average group size. Finally, a critical test is proposed of the hypothesis that increasing group size should lead to reduced predation risk by comparing demographic patterns between areas where predators are still present and where they have disappeared. A total of 23 data sets on 13 species were extracted from the literature and supplemented with four unpublished data sets. In all three tests the results provide strong support for the predation-feeding competition theory and are clearly unfavourable for the theory postulating feeding advantages to group living. Such feeding advantages may, however, gain prominence under some conditions.

On the ultimate causes of primate social systems.

Abstract: [The aim of this review is to present a coherent explanation of the ultimate causation and the evolution of primary social systems. The explanation is based on the assumption that social systems of all diurnal primates are derived from female defence polygyny. Group living is therefore regarded as the essential first step in the social evolution of diurnal primates. Primate social systems are generally classified into four main types, each of which can be contrasted with the others along the following lines: solitariness versus group living, monogamy versus polygyny and reproductive activity by only one male versus reproduction of several males per group. First of all we present some comparative evidence to support the hypothesis that monogamy in primates has evolved from polygynous groups, in two different ways. A commonly held view is that monogamy is most likely to develop where paternal care of the offspring is advantageous. This is almost certainly the case in the very small species of primates. In these monogamy is the consequence of twinning and the resultant need for active paternal care. It runs contrary to the evident tendency of these species to form larger groups in response to the pressure of predation. The latter is achieved by an extended group membership of grown-up offspring in a non-reproductive and even 'helping' role. In the larger species, however, monogamy is most probably the outcome of, on the one hand, a strong need to reduce competition for food favouring very small group sizes, and, on the other hand, of the virtual absence of predation permitting such a development. Secondly, we look critically at several hypothetical explanations for the existence of multi-male groups and one-male groups. We argue that the ultimate explanation for their existence is not to be found in differential male mortality, anti-predator defence, availability of food, and differential expulsion of "expendable" males. Instead, comparative evidence indicates that the distinction between a single-male or a multi-male system is ultimately dependent on the varying ability of a male to monopolize access to a breeding group of females. This ability in turn depends on group cohesiveness as determined by feeding strategies and predation pressure and is often, though not necessarily, related to the size of the group., The aim of this review is to present a coherent explanation of the ultimate causation and the evolution of primary social systems. The explanation is based on the assumption that social systems of all diurnal primates are derived from female defence polygyny. Group living is therefore regarded as the essential first step in the social evolution of diurnal primates. Primate social systems are generally classified into four main types, each of which can be contrasted with the others along the following lines: solitariness versus group living, monogamy versus polygyny and reproductive activity by only one male versus reproduction of several males per group. First of all we present some comparative evidence to support the hypothesis that monogamy in primates has evolved from polygynous groups, in two different ways. A commonly held view is that monogamy is most likely to develop where paternal care of the offspring is advantageous. This is almost certainly the case in the very small species of primates. In these monogamy is the consequence of twinning and the resultant need for active paternal care. It runs contrary to the evident tendency of these species to form larger groups in response to the pressure of predation. The latter is achieved by an extended group membership of grown-up offspring in a non-reproductive and even 'helping' role. In the larger species, however, monogamy is most probably the outcome of, on the one hand, a strong need to reduce competition for food favouring very small group sizes, and, on the other hand, of the virtual absence of predation permitting such a development. Secondly, we look critically at several hypothetical explanations for the existence of multi-male groups and one-male groups. We argue that the ultimate explanation for their existence is not to be found in differential male mortality, anti-predator defence, availability of food, and differential expulsion of "expendable" males. Instead, comparative evidence indicates that the distinction between a single-male or a multi-male system is ultimately dependent on the varying ability of a male to monopolize access to a breeding group of females. This ability in turn depends on group cohesiveness as determined by feeding strategies and predation pressure and is often, though not necessarily, related to the size of the group.]

Reconciliation and Redirected Affection in Rhesus Monkeys

Abstract: The question whether rhesus monkeys reconcile was empirically translated as: Do they seek non-agonistic contact with former adversaries? The study concerned a captive group of forty-one monkeys, Macaca mulatta. Participants in 350 aggressive incidents were followed both immediately after the incident and during matched control periods. Comparison of the two sets of data showed that: - After the incident former opponents had an increased tendency to approach and contact each other. - The attraction between them was selective, i.e., the number of inter-opponent contacts showed not only an absolute but also a relative increase. - Also former alliance partners showed attraction to each other. - Inter-opponent contacts were behaviorally distinctive. The most characteristic behavior patterns were embrace, lipsmack and redirected threat. - Conciliatory tendency increased with general bond strength between individuals, even though the first measure had a built-in correction for the second. - A higher conciliatory tendency among matrilineal relatives could be fully explained by the above mentioned influence of bond strength. - General effects of agonistic interactions included a grooming increase for violent aggressors, a grooming decrease for victim of severe aggression, and an increased receipt of grooming for mild aggressors. - Grooming of outsiders by violent aggressors depended on the intensity of the bond between aggressor and victim. Therefore, this grooming behavior was interpreted as redirected affection.

Optimisation of Nut-Cracking With Natural Hammers By Wild Chimpanzees

Abstract: The chimpanzees of the Tai National Park, Ivory Coast, use sticks and stones to open 5 different species of nuts. In spite of an unfavourable availability of the material in the forest, the animals choose their tools adaptively. For cracking harder nuts, they use harder and heavier tools and transport tools more often and from farther away. Some aspects of the evolution of tool-use in primates are discussed.

Forced Copulation in Waterfowl

Abstract: 1. Although almost all waterfowl (ducks, geese and swans comprizing the family Anatidae) have basically monogamous mating systems, males of 39 species have been observed to perform or attempt forced copulation (FC) (previously called "rape"). 2. Suggestions that FC is an artifact of crowding in urban mallards, an outlet for thwarted male sex drive, a component of territory defence, or an alternative reproductive strategy of unpaired males are not supported by available evidence. 3. In the case of the mallard, HEINROTH'S (1911) interpretation of FC as a secondary insemination method whereby paired males increase their reproductive success by fertilizing some of the eggs laid by females other than their mate is supported by evidence of various kinds. FCs are performed by paired males; they occur during periods in the breeding season when eggs are being fertilized; they are directed mainly at females in prelaying and laying condition; paired males usually defend their mates against males attempting FC (suggesting defence of genetic paternity); paired males have been seen to copulate forcibly with their own mates after the latter have been subjected to FC (suggesting an antidote insemination strategy). 4. Experiments on captive mallards have shown that eggs can be fertilized by sperm delivered during FC and, since females can store viable sperm for up to 17 days, sperm competition must be taking place. Artificial insemination experiments have shown that (a) the second of 2 competing inseminations 6 hours apart overlays the former insemination and is 70% more potent, (b) there is an insemination "window" within 1 hour of oviposition when the next egg in the clutch is fertilized. The extent to which males time their copulations (FCs, pair copulations, forced pair copulations) to take advantage of these patterns of sperm competition is not known. 5. Studies of the lesser snow goose, northern pintail and lesser scaup indicate that FC is a secondary reproductive strategy of paired males in these species also. Observations on 13 species of dabbling duck provide additional evidence for the selection of fertile females as FC targets and the development of male tactics for achieving and combatting FC. 6. It is difficult to rule out the possibility that females could derive certain benefits from FC inseminations (e.g. genetic diversity of offspring) but the costs and risks of being involved in FC assaults can be high and the females apparently try to avoid FC. Female dabbling ducks can be damaged, or even killed, during assaults and female escape behaviour (high flights, diving, hiding in cover) entails energetic costs and wastage of time that are presumably detrimental to females during the period when they are producing eggs. 7. As HEINROTH suggested, FC probably does not occur in swans, most geese and shelducks because it is incompatible with the major roles that paired males play in defence of breeding territories, mates, nest-sites and broods in these groups. The occurrence of FC in snow and Ross goose may be facilitated by colonial nesting.. 8. Among dabbling ducks, male territoriality is associated with strong mate-guarding and these characteristics appear to conflict with male FC activities. Involvement of paired males in extrapair courtship, polygyny and brood-care may produce additional conflicts with FC behaviour in certain species. 9. In at least 4 species of waterfowl (mallard, northern pintail, lesser snow goose, lesser scaup) behavioural evidence indicates that FC is part of a mixed male reproductive strategy of the type postulated by TRIVERS (1972). Rigorous testing of the hypothesis will require studies to (a) assess the incidence of multiple paternity in wild clutches, (b) distinguish species (or populations within a species) in which paired males actively pursue FC tactics from those in which they merely capitalize on incidental opportunities for FC.

Male competition in large groups of wintering humpback whales

Abstract: Fast moving groups containing three or more adult humpback whales are found in the winter on Silver Bank in the West Indies, and off Hawaii. Many of these groups have a definite structure: a central Nuclear Animal, with or without a calf, is surrounded by escorts who compete, sometimes violently, for proximity to the Nuclear Animal. This competition involves fluke thrashes, the blowing of bubblestreams, and physical contact, some of which appears designed to hurt an opponent: bleeding wounds are seen on the competing escorts. Escorts sometimes leave these groups and start singing, and singers sometimes stop to join large groups. The pattern of interactions strongly suggests that the escorts are males competing for access to a central female. Off Hawaii singers respond to such groups at ranges of up to approximately 7.5 km. On Silver Bank, Principal Escorts maintained a position of closest proximity to the Nuclear Animal for an average of 7.5 hours before replacement.

Nipple Location By Newborn Rabbits: Behavioural Evidence for Pheromonal Guidance

Abstract: In einem mit Glasboden versehenen Nistkasten wurde das Saugverhalten neugeborener Hauskaninchen von unten beobachtet (3 Wurfe). Durch Experimente, in denen der Bauch der Hasin rasiert und in verschiedener Weise abgedeckt worden war, wurden die relevanten Reize fur das Auffinden der Zitzen untersucht (16 Wurfe). 1. Kaninchenjunge konnen bereits wenige Sekunden nach Ankunft der Mutter Zitzen finden und besaugen. Auf Vibrations- und Beruhrungsreize reagieren sie mit AufrichtBewegungen. Sobald sie mit dem Fell der Hasin in Kontakt kommen, stosen sie ihre Schnauzen tiefer und fuhren die fur Zitzensuchverhalten typischen, senkrechten (Proben) und seitlichen Kopfbewegungen aus, bis sie eine Zitze ergriffen haben. 2. Das Zitzensuchverhalten wird durch Geruchsstoffe der Haut ausgelost und aufrecht erhalten. Die Starke des Geruchs scheint in Richtung Zitzen zuzunehmen und besonders hohe Konzentrationen an der Zitzenbasis oder ein moglicher zweiter Geruch losen das Ergreifen der Zitzen aus. 3. Wegen der geringen Reichweite des Geruchs hilft wahrscheinlich das Fell der Mutter den Jungen Kontakt mit der Bauch aufzunehmen und zu bewahren, und durch Verstarkung der seitlichen Kopfbewegungen den Geruchsgradienten zu entdecken. Jedoch sind fur das Auffinden der Zitzen weder der Fellstrich noch Temperaturgradienten der Haut wichtig. 4. Von der gesamten Saugezeit, pro Tag 3-4 Minuten, benotigten die Hasinen im Mittel 5,2 sec, um die Saugehaltung einzunehmen, die Jungen 11,5 sec (Median), um das Bauchfell der Mutter zu erreichen und 6,0 sec (Median), zum Zitzen zu finden und zu ergreifen. Unerwartet war, das Kaninchenjunge haufig Zitzen loslassen und wechseln, im Mittel 2,5 mal pro Minute, wodurch sich die an Zitzen insgesamt verbrachte Zeit weiter reduzierte. Jedoch nahm mit dem Alter auch die Leistungsfahigkeit der Jungen zu und der relative Anteil der eigentlichen Saugezeit erhohte sich wahrend der ersten 12 Lebens-tage von circa 47% auf 72%. 5. Der Zitzensuchverhalten auslosende Geruch kann als ein Pheromon im eigentlichen Sinn angesehen werden, da ein stereotypes Verhalten reproduzierbar ausgelost wird.

The dawn chorus in the great tit (parus-major) - proximate and ultimate causes

Abstract: The dawn chorus of the great tit can be interpreted from a functional point of view in terms of the following factors. (i) Climatic and other physical conditions in the early morning are unfavourable for foraging and favourable for acoustic communication. (ii) Overnight accumulation of territories favours early morning invasion by potential settlers. (iii) The combination of (i) and (ii) favours early morning territorial defence, including song. A laboratory experiment designed to investigate the proximate causes of allocation of time by territorial great tits to foraging vs. territorial activities (including song) showed that birds are more responsive to intruders when food availability is low. We discuss the relevance of our results to the dawn chorus in other animals and in other geographical regions.

Oestrous Behaviour and Female Choice in the African Elephant

Abstract: 1. During the course of an eight year field study of African elephants in Amboseli National Park, Kenya, from September, 1972 to December, 1980, females were seen exhibiting oestrous behaviour on 154 occasions, during which 43 copulations were witnessed. 2. Five categories of oestrous behaviour are described: a) wariness, b) the oestrous walk, c) the chase, d) mounting, and e) consort behaviour. 3. The oestrous behaviour as described was found to be temporally associated with ovulation, as judged by conceptions, in 70.7% of 58 cases. 4. The duration of oestrous periods is estimated at 2-6 days. 5. On average Amboseli females conceived once every 5 years and for each of these conceptions the female may only have been in oestrus once. 6. Evidence from the Amboseli study suggests that some females may exercise choice in mating partners. For example, females were able to elude their pursuers in 69.4% of all chases (n = 134). Observation of female behaviour during oestrus suggested that some females preferred to mate with males in the largest size class, particularly those in musth. 7. Two possible short-term advantages to females exercising choice in mating partners are suggested: a) avoidance of harassment from other bulls; and b) Large males in musth may be more likely to impregnate a female. 8. A possible long-term advantage to mating with a Large, and therefore older, male could be his ability to pass on a trait for longevity. 9. Although females may be exercising choice among the size/age classes, male-male competition among the Large males may override female choice on the individual level.

Shell Wars: Assessment Strategies and the Timing of Decisions in Hermit Crab Shell Fights

Abstract: The shell fighting behaviour of the hermit crab Pagurus bernhardus was observed under experimental conditions. The relative sizes of the crabs and shell quality of the larger crab influenced the probability of occurrence of a shell fight. These two factors along with the quality of the smaller crab's shell influenced the probability of an escalated fight occurring. During a shell fight, the attacker was able to assimilate information concerning the defender's shell and to compare it with the shell in possession. On the basis of this comparison the attacker decided whether or not to evict the defender and effect a shell change. The time that the attacker took in assessment of the opponent's shell was influenced by a) the quality of the attacker's own shell and b) the ease of discrimination between the qualities of the two shells. Thus decisions were easier in some instances than in others. The defending crab did not have access to information about the attacker's shell and therefore could only estimate the quality of its own shell. This asymmetry of information experienced by the crabs ensured that the attacker decided the outcome of a shell fight.

Quatic Foraging in Garter Snakes: a Comparison of Specialists and Generalists

Abstract: To examine the assumption, underlying much ecological theory, that a "Jack-of-all-trades is master of none", a comparison was made of the aquatic predation of four colubrid snakes, two aquatic specialists (Thamnophis couchi, T. melanogaster) and two terrestrial-aquatic generalists (T. sirtalis, and T. elegans). Observations were made in the field, then juvenile snakes were compared under controlled laboratory conditions. The specialists and generalists had qualitatively different foraging repertoires. The specialists made lengthy dives, crawled slowly on the underwater substrate and made long-distance underwater responses to prey: orientation, approach, pursuit, and frontal attack. The generalists dived briefly, with rapid serpentine locomotion, or searched "terrestrially" by wandering along the shoreline and snatching prey from the water surface. Underwater, the generalists' only prey-directed response was sudden short-distance attack, and they appeared to rely on chance encounters with prey. There were significant differences between the two pairs. In comparison with the generalists, the specialists 1) captured more fish, 2) spent more time on aquatic search, 3) spent more aquatic search time diving, 4) spent more diving time on the underwater substrate, 5) made more attacks in every category of search in open water, and 6) attacked underwater from a greater distance. Significant differences were not found in attack frequencies in those search categories where underwater vision is probably unimportant (aerial attacks and attacks in underwater crevices), nor in aerial attack distances. The specialists' behavioral superiority in respect of their specialization supports the "Jack-of-all-trades" assumption. The observations suggest that this superiority is associated with superior underwater visual acuity (which may be due to superior visual accommodation). The generalists' principal underwater searching technique (serpentine diving) appears to be energetically costly, and may only be profitable when aquatic prey are especially vulnerable. Nerodia sipedon, member of a genus that is closely related to Thamnophis but more aquatic, had a foraging repertoire qualitatively similar to that of the generalists. The similarity may be associated with N. sipedon's nocturnal habits and presumed reliance on non-visual prey cues.

Experiential Effects On Agonistic Behavior in the Paradise Fish, Macropodus Opercularis

Abstract: The effects of prior dominance experience on agonistic behavior were investigated in male paradise fish, Macropodus opercularis, with particular reference to the social conditioning hypothesis. The subjects had only limited social experience prior to the pre-test treatments; their pre-test dominance histories were controlled experimentally, through rigged contests (based on relative size). Following the pre-test conditioning treatments, the treated fish were paired with naive siblings of the same standard length, and subjected to a battery of four tests: two measures of aggressiveness, one of reactivity and one of social dominance. The latter consisted of a dyadic encounter with a naive sibling in a neutral aquarium. Four separate experiments were conducted, each exploring a different parameter of social dominance. It was found that negative dominance experience resulted in a significant decrement in subsequent dominance success and in increased reactivity levels, but had no influence on the measures of aggressiveness. Positive dominance experience had no effect on any of the response measures. The implications of the asymmetry in the effects of dominance experience (particularly with regard to subsequent dominance scores) for the social conditioning hypothesis and the associationist paradigm in general, as it applies to agonistic behavior, were explored. It was concluded that the social conditioning hypothesis cannot account for the results obtained here or for those of related studies. The relationships between the measures of aggressiveness and the measure of social dominance were also discussed.

Variability in the Responses of Black-Billed Magpies To Natural Predators

Abstract: Encounters between black-billed magpies (Pica pica) and a variety of natural predators were observed during 3 breeding seasons in Wind Cave National Park, South Dakota. How a magpie responded to a potential predator appeared to depend on (1) the type of predator and the threat it posed to magpie eggs, nestlings, fledglings, and adults; (2) the behavior of the predator; and (3) the reproductive stage of the magpie. Raptors were the most frequently encountered potential predators, with magpies reacting more strongly to falcons than to hawks. Reactions to crows and squirrels were most frequent and intense during laying and incubation, while raptors in flight and coyotes were responded to most vigorously during the second half of the nestling period and the first two weeks of fledgling. Perched raptors were almost always mobbed vigorously. Diving to within 2 m of a predator appeared to be effective in driving it away. The roles of chasing and alarm calling were less clear, but in addition to alerting mates and offspring to danger, such behavior would impede efficient hunting by the predator and so might contribute to its departure. Only one successful act of predation was observed, but the evidence suggested that owls, hawks and falcons were responsible for most fledgling and adult mortality. No clear cases of nest predation by crows or squirrels occurred, but some clutches of eggs and broods of young nestlings disappeared. Although mates usually mobbed predators together, males were slightly more active, possibly because males were larger and because females were often occupied in the nest with incubation and brooding. Observations of wild fledglings and hand-raised magpies suggest that magpies have an innate fear response to a variety of stimuli and that fledglings gradually learn what to continue fearing from parents, other magpies, and their own experiences. I suggest that although parental investment theory may be basically correct in predicting that young increase in value to their parent as they approach independence, a variety of other factors may affect anti-predator behavior, such as (1) the types of predators likely to be encountered and the relative danger they pose to different age classes; (2) the ability of the parents to successfully drive off a particular predator; (3) the ability of the parents to re-nest that year; (4) the likelihood that a pair will be able to fledge young the following year.

Determinants of Dominance in Male Sticklebacks (Gasterosteus Aculeatus L.)

Abstract: When two males of the three-spined stickleback (Gasterosteus aculeatus L.) in reproductive condition are placed in a tank of small size, one becomes dominant over the other in a very short time. In this way a group of isolated reproductive males were tested pairwise on their capacity to become dominant. It appeared that the males could be arranged in a linear order of dominance. Their rank was to some extent correlated with their territorial aggressiveness as assessed in other tests. Their experience in previous dominance tests played a more important role. The brightness of their colouration, however, was probably the most consistent and decisive determinant of dominance. The interaction of colour and experience could be traced in the outcome of the dominance tests. The occurrence of roundabout fighting is discussed.

A Synthesis of Sleep in Wild Birds

Abstract: In this synthesis we have attempted to survey and reanalyse the current literature concerning bird sleep. This was achieved by first reviewing present theory describing functions of sleep. Two general models surfaced which encompass many of the specific sleep theories, namely homeostatic and ecological theories. The terminology used to describe sleep and other associated behaviour was organized into an operational hierarchy. We defined loafing behaviour as a general state of immobility. This functional heterogenous group may include comfort behaviour, feeding, social interaction, wariness, staring down and inactive behaviour. Sleep and associated behaviour are considered inactive behaviour. We next described the common sleeping postures as follows: 1. Bill on back or under scapulars; the classical sleep posture. 2. Bill forward or rest-sleep posture. 3. Head on ground. Specific sleep characteristics were also identified as: 1. Quality of sleep based on duration and frequency of eyelid closure. 2. Length of sleep, called sleep session time which is based on the summation of sleep bouts. A sleep bout is defined as the time elapsed during eye closure and opening. 3. Temporal patterning of sleep sessions which are suggested to be dependent on timing of other higher priority behaviours. 4. The resilience (flexibility) of sleep session time. An original analysis was conducted on these sleep characteristics and other environmental, constitutional, behavioural and predation factors. The results indicated that birds experiencing longer daylength slept less each day. Further, birds slept less if (1) overall dangers were greater and (2) they were more communal sleepers. Longer sleep session times were associated with greater exposure while sleeping (i.e. on a lake or mud flat). Several possible functions of sleep were then suggested. Protection theories encompass choice of a safe sleep site while addressing the significance of communal roosting. Recuperation theories were not adequately supported by quantitative studies. Energy conservation theories imply that birds sleep when doing other behaviour might be non-productive. We suggest a model based on eyelid blinking which allows for a degree of vigilance during sleep but which is also compatible with minimizing energy expenditure.

Alternative mechanisms of social organization in monkeys

Abstract: Observations on a captive group of patas monkeys were supplemented with field observations to analyse the process by which a gregarious animal keeps track of the position and activity of other group members and regulates the distance between them and itself. This process can take place without the exchange of specialised signals (displays) and is described as a mechanism of group organisation alternative to a mechanism based on the exchange of displays. Displays and formalised interaction patterns can provide additional, complementary information, especially about transient features of social organisation.

The Characterisation of Stereotyped Behaviour in Stalled Sows By Informational Redundancy

Abstract: This investigation on stereotypies of domestic sows has two aims: 1) to investigate the behavioural profiles shown in the different parities and stages of the reproductive cycle, and 2) to characterise stereotypies by descriptive qualitative and quantitative parameters. As the commonly used functional characteristics of stereotypies were felt to be largely hypothetical at this stage, preventing a deeper understanding of this abnormal behaviour, two purely descriptive approaches were adopted: the first one separated such behaviour from other activities by intuitively essential features, that were condensed into an operational definition. Observations were made on the intensively kept sows of the Edinburgh School of Agriculture pig unit kept in the dry sow house and the lactating sow stalls. From scanning surveys and continuous focal animal samples, behavioural profiles were obtained for the sows of different ages and physiological states. Parity 1 was characterised by frequent and long lasting drowsy stances which probably were a "cut-off" reaction to the unfamiliar Dry-Sow-House environment. In parity 2 and 3 the sows showed increased investigative and manipulative behaviour, but also rapidly emerging stereotyped activities. These increased in kind, frequency and duration over the parities, but were confined to the pregnant animals in the dry sow stalls and virtually absent from the lactating sows which could interact with their piglets. The second approach was to measure the general repetitivity in the behavioural sequences by quantifying their informational content with the redundancy measure C. Both appraoches largely agreed when the intuitively defined stereotyped or non-stereotyped sections of behaviour were assessed for redundancy, the former being significantly more redundant in spite of overlapping C-values. The redundancy of all behaviour, summing variable, positional and stereotyped activities, gradually rose with parity through all cycle stages. In part this was due to the increasing proportion of the intuitively stereotyped sequences, and in part to the increasing redundancy of the remaining variable activity. The redundancy in the stereotyped sequences however remained fairly constant once they were established, and were in all parities well above the levels of variable behaviour. In order to appropriately compare stereotyped and variable activity, redundancies were not only calculated relative to the entire range of elements observed in the stalled dry sows, but also relative to the restricted range of the active elements of all or of each individual sow. All ANOVAs showed significant increases of redundancy over parities, but no effects of pregnancy or interaction to parity. In the discussion the two approaches are compared; from the process of acquiring the sterotypies we then derived the hypothesis, that a likely function could be to reach homeostasis in arousal by warding-off external stimuli and self-generating known sensory input. So far there is nevertheless firm evidence, that stereotypies are signs of major behavioural problems and of concurrently impaired welfare, especially at times of acquisition.

The Territorial Prior Residence Effect in Convict Cichlids (Cichlasoma Nigrofasciatum GÜNther): Temporal Aspects of Establishment and Retention, and Proximate Mechanisms

Abstract: [In a series of six laboratory experiments, the time course of development, retention function, and some possible proximate mechanisms underlying the territorial prior residence effect (resident dominance advantage over conspecific intruders) were examined using the territorial convict cichlid, Cichlasoma nigrofasciatum Gunther. In each experiment direct encounters took place between a resident and a like-sized conspecific intruder. In Experiments 1 and 2 it was determined that the resident must be sole occupant of an area for somewhere between 24-48 hours before successfully dominating an intruder. Experiment 3 showed that residents removed from their territories after 3 days residence, placed in an extraterritorial tank for 1 or 2 hours, and then replaced in their territories demonstrated significant dominance over intruders after the 1 hour removal but not the 2 hour removal condition. In Experiment 4, the hypothesis that a resident may become dominant in its territory because of habituation of fear responses in it (neophobia) was tested. Residents were given 3 days to acclimate to an area and were then removed to one of three extraterritorial environments that varied in similarity to the home territory. In general, the greater the extraterritorial dissimilarity to the home territory, the greater was the disruption of the prior residence effect after being returned to the home tank. Apparently, the dissimilar extraterritorial environments dishabituated the animals' habituation of fear to the home environment. Experiments 5 and 6 revealed that the presence of the territorial marker (shelter) during a territorial intrusion is neither necessary nor sufficient in producing the prior residence effect. In almost all of the present experiments, as in past ones, where the prior residence effect was shown the resident reliably attacked first. Also, biting first, in general, was a reliable predictor of eventual dominance. Proximate and ultimate mechanismus underlying the occurence of the prior residence effect in the field and in the laboratory are discussed., In a series of six laboratory experiments, the time course of development, retention function, and some possible proximate mechanisms underlying the territorial prior residence effect (resident dominance advantage over conspecific intruders) were examined using the territorial convict cichlid, Cichlasoma nigrofasciatum Gunther. In each experiment direct encounters took place between a resident and a like-sized conspecific intruder. In Experiments 1 and 2 it was determined that the resident must be sole occupant of an area for somewhere between 24-48 hours before successfully dominating an intruder. Experiment 3 showed that residents removed from their territories after 3 days residence, placed in an extraterritorial tank for 1 or 2 hours, and then replaced in their territories demonstrated significant dominance over intruders after the 1 hour removal but not the 2 hour removal condition. In Experiment 4, the hypothesis that a resident may become dominant in its territory because of habituation of fear responses in it (neophobia) was tested. Residents were given 3 days to acclimate to an area and were then removed to one of three extraterritorial environments that varied in similarity to the home territory. In general, the greater the extraterritorial dissimilarity to the home territory, the greater was the disruption of the prior residence effect after being returned to the home tank. Apparently, the dissimilar extraterritorial environments dishabituated the animals' habituation of fear to the home environment. Experiments 5 and 6 revealed that the presence of the territorial marker (shelter) during a territorial intrusion is neither necessary nor sufficient in producing the prior residence effect. In almost all of the present experiments, as in past ones, where the prior residence effect was shown the resident reliably attacked first. Also, biting first, in general, was a reliable predictor of eventual dominance. Proximate and ultimate mechanismus underlying the occurence of the prior residence effect in the field and in the laboratory are discussed.]

Reproductive Behaviour of the Lesser Waxmoth, Achroia Grisella (Pyralidae: Galleriinae): Signalling, Pair Formation, Male Interactions, and Mate Guarding

Abstract: Laboratory experimentation and field observations of the lesser waxmoth revealed marked differences in reproductive behaviour from other Lepidoptera. Males emit a long-range signal, stationary wing-fanning combined with release of a 2-component pheromone, continuously during scotophase. Pheromonal release rates are 10-1000 x those known for female-emitted pheromones in other moths. However, the energetic cost of wing-fanning is very low relative to known values for similar activities in other male insects. In the field, signalling occurs in the vicinity of the larval food resource, beehives, the precise location (within or on the exterior of the hive) depending on the honeybee population size. Matings were observed during the initial half of the night. During pair formation, females usually run directly toward a signalling male. Female approach behaviour at close range is rather unstereotyped. They may directly contact the male, wing-fan and/or circle in close proximity, or remain stationary until the male initiates courthip. When provided with a choice of a wing-fanning male and a non-wingfanning one separated by > 10 cm, females always approach the wing-fanning individual. If only non-Wing-Fanning males are present, young females never approach, but older females, which typically move more extensively than younger individuals, sometimes approach and mate. Males in close proximity to one another, whether in laboratory chambers or at beehives, interact in various ways. A higher proportion of males in groups signal than solitary males, and when the first male in a group begins signalling, the other moths initiate signalling shortly thereafter. Nevertheless, a small proportion of males signal infrequently or not at all, and these males sometimes remain very close to signallers. When a female is presented with a pair of males as above, she occasionally mates with the non-signaller. In these circumstances, the non-signaller responded to the female's close-range approach and began wing-fanning. Non-signalling males do not enjoy greater longevity in the laboratory, despite their reduced consumption of energy. Aggregated males fight by running, while wing-fanning, at neighbours. The respondents of such attacks are usually signalling males. Males usually resume signalling soon after copulation. Individuals that remate within a short period remain in copula for a very extended length of time. These extended copulations occur because the male cannot immediately transfer a spermatophore, and therefore comprise a form of pre-fertilization mate guarding. Females show no preference for virgin or previously-mated males and do not attempt to interrupt extended copulations. The unusual system, for Lepidoptera, of pair formation in the lesser waxmoth is viewed as a response to an aggregated resource structure which renders searching for mates relatively low in risk and expenditure of energy. Consequently, females assume this role. The other non-lepidopteran aspects of the mating system evolved as a result of this sex-role reversal in pair formation and the aggregation of adult males at the larval food resource.

Dynamics of Territorial Singing Between Neighboring Song Sparrows (Melospiza Melodia)

Abstract: 1. Countersinging song sparrows (n = 6) interact by coordinating the turnover of their song bouts, but long-term leader/follower roles generally do not occur in song switching. In contrast, varition in the sequencing of song types and in the rate of singing are not influenced by that of countersinging neighbors. 2. Singing was divided into four behavioral contexts (soloing, countersinging, pre-fight and post-fight) in which the intensity of agonistic stimulation was assumed to increase. Both bout lengths and the coordination of song switching with perch changing showed consistent relationships with stimulus intensity; however, the periods of songs (a measure of timing) showed no such relationship. 3. The relative frequencies of occurrence of song types within repertoires changed across the four behavioral contexts, although this change could be a by-product of the correlation between bout length and context. 4. In general, variations in the song sparrow's rate of switching song types are used in short-term interactions involving territorial defense, but variation in song type sequencing and song rates are not used. The benefits of song switching (which require the possession of at least two song types) cannot explain the origin of larger repertoires of song types. 5. We suggested these benefits may be the transmission of directional and motivational information. Given the large repertoires and low song sharing of this population, song switching may be better adapted for obtaining these benefits than song sequencing or song rates. 6. The tendency to coordinate song switches with perch changes was predicted by the Beau Geste hypothesis (KREBS, 1977), which assumes that singing is directed to unestablished floater seeking a territory. However, since this coordination tends to increase with increasing stimulation provided by territorial neighbors, it does not exclusively support the Beau Geste hypothesis.

Magnetic Field Orientation of Migratory Savannah Sparrows With Different First Summer Experience

Abstract: Three groups of hand-reared savannah sparrows (Passerculus sandwichensis) were given different exposure to the sky and an ambient magnetic field during their first summer to investigate the possible effect of experience on the magnetic field orientation of their first autumn migration. Whether ever having seen the sky or not, birds raised exposed to local earth's magnetic field showed the same directional orientation during tests in the local earth's magnetic field. Birds with prior experience with the sky were perhaps better oriented. Birds that were raised outdoors in a 90° shifted magnetic field, however, oriented differently during tests in the local earth's magnetic field. Their orientation tended to be orthogonal to the other groups. The data show that first summer experience can influence the magnetic field orientation of migratory savannah sparrows and in a way which suggests the possibility of a calibration process.

The Feeding Behaviour of Grazing African Ungulates

Abstract: The second to second organization of the foraging behaviour of eleven species of African ungulates is described, with particular emphasis on locomotion while foraging and on the time spent feeding. It was predicted that foraging behaviour should change with the species' body size and stomach specialization and, within a species, with the seasonal or spatial changes in the quality and availability of the food supply. A feeding site was defined as the area which a feeding animal could reach without moving either of its forefeet. Feeding subjects thus encountered a new site every time they took a step with either forefoot and foraging behaviour could be described in terms of the organization of a series of behavioural events (steps) and bouts of activity (feeding). Five indices were used to summarize all records obtained. Only one of these, the proportion of time spent feeding, was significantly correlated with the species' body size. The other four indices include: the rate of movement (in steps per second), the mean feeding time per step, the proportion of sites encountered which carried at least some acceptable food, and the mean time spent feeding from those accepted sites. These last four indices were apparently more strongly affected by the species' stomach specialization than by its body size. The five species with the largest sample sizes (reedbuck, impala, tsessebe, wildebeeste, buffalo) were used to investigate the tendency found within all study species for foraging behaviour to vary seasonally. Firstly, both the mean feeding time per step and the mean feeding time per accepted site were found to be positively correlated with indicators of vegetation bulk and maturity, but negatively correlated with an index of fresh green growth, for all five species: it is suggested that this is due to changes in both the amount of food taken from a given site and in the time needed to ingest a given bulk of food. Secondly, the organization of events within foraging sessions (described in terms of the frequency distributions of step intervals, feeding durations, and the lengths of runs of acceptance or rejection of feeding sites) varied through the year: in particular, food patch size, indicated by the length of sequences of accepted sites, was apparently largest just before the end of the rains, when the vegetation should have been most uniform in quality. Thirdly, the reedbuck is a specialist grazer which, because of its body size, might be expected to feed very selectively within the grass layer: the feeding behaviours of the other four species most closely resembled that of the reedbuck when these four species were feeding off long grass in the dry season, conditions which presented them with much low quality food senescent grass hampering access to very small amounts of higher quality green matter. It is suggested that, as in domestic ungulates, feeding behaviour varies within a species with the proportion of low fibre, high protein, green growth in the vegetation, and in the contrast in quality between the various plant parts. A multivariate analysis was used to identify the foraging characteristics of individual ruminant species. Species which were specialist grass feeders (bulk/roughage feeders) encountered more sites more predictably, and spent more time feeding off those sites, than did species which were known to switch from grasses to other food sources to take advantage of changes in the relative quantity and abundance of food types in the habitat (intermediate feeders). It is suggested that, since pure grazers' foraging is limited to a fairly continuously distributed food supply, their foraging consists mainly of teasing out and biting off grass leaves and the organization of their foraging behaviour is determined by the structure and quality of the grass sward. Intermediate feeders, on the other hand, had the option of taking higher quality but less continuously distributed items, such as fruits, and their foraging may have involved seeking out and moving between such items. Pure grazers' foraging behaviour is thus seen as being dominated by food capture and handling events, while intermediate feeders may be more strongly influenced by food search or pursuit requirements. It is likely that grazers differed from intermediate feeders not only in the basic organization of their foraging behaviour, but also in the way that this organization was affected by the species' body size.

Movement orders and leadership in a semi-wild cattle herd

Abstract: Stable movement orders have been found in a semi-wild cattle herd. Orders of voluntary movements (2-4 km to and from nocturnal resting site) were correlated with each other but not with the order of foced movement (dipping). The individual average travelling positions as well as their standard deviations showed no significant dependency on age or on dominance. A tendency for old (experienced) animals to walk in the van and for young ones to make up the rear was only evidenced during forced movement. Calves travelled in the neighbourhood of their dams. It was concluded that the conservative retainment of particular movement positions is primed by matrilineal tradition. The single adult bull consistently walked in the rear group of the moving mob. It was only during encounters with strange cattle that he temporarily took the leadership and actively hindered his animals from mixing with the other herd. Each kind of herd movement was preceded by a different leader cow who regularly walked on position No. 1. During voluntary movements the herd showed a certain dependency on its leader, and it was up to her to make the decision when to start moving away from one location and which direction to choose. In cow Alma spatial leadership was traced over a period of five years. Leadership showed no strict dependency on age or dominance.

The Food Storage Behaviour of the Northwestern Crow

Abstract: The food storage behaviour of the Northwestern crow (Corvus caurinus) was investigated on Mitlenatch Island, British Columbia. The crows stored mostly intertidal food, especially clams, crabs, fish and worms, on the hillsides surrounding the intertidal beach. They also carried food to other parts of the island, presumably to be stored. Storage sites included, in decreasing order of importance, grass clumps, moss banks and the sides of rocks. The choice of substrate is discussed in relation to its camouflaging effect. Food items were most often carried and stored singly. Some individuals carried two items at a time. On average, it took a crow 24.9 sec to hide a food item. The crows stored food in exclusive and non-exclusive areas. Exclusive areas were defended and associated with a nesting territory, whereas non-exclusive areas were not, resulting in several birds using them. Food items were almost always covered and it was shown experimentally that this significantly reduced the chance that the cached item was stolen. The availability, abundance, profitability and preservation qualities of the stored food were discussed. Storage seems to result from a relative scarcity of non-intertidal food at high tide early in the breeding season. During this period too, females are forming and laying eggs, and may depend on the stored food at high tide. The success of 3-colour-ringed crows in relocating their food caches was 76%. The birds appeared to have memorized the location of their food stores. Olfaction appeared to be unimportant for the detection of experimentally-hidden clams. Experiments demonstrated that single stored clams were found more slowly than clumped ones. The problem of stored food decomposition was studied and discussed in relation to the short-term storage strategy.

Sexual Selection in the Great Plains Toad (Bufo Cognatus)

Abstract: Breeding aggregations of Bufo cognatus were observed in southern Arizona and southwestern New Mexico during June, July and August, 1980-82 Most breeding aggregations lasted only two or three nights following summer rainstorms Males substantially outnumbered females at choruses, and females actively selected mates from among displaying males Some small males adopted satellite positions near calling males, and the percentage of time a male was observed calling was significantly correlated with snout-vent length Male mating success was positively correlated with the percentage of time a male was observed calling, but male size and mating success were not correlated There was no indication of positive assortative mating with respect to body size It is concluded that Bufo cognatus has a lek mating system

Notes On the Behavior of Euprymna Scolopes (Cephalopoda: Sepiolidae)

Abstract: 18 individuals of the sepiolid Euprymna scolopes were collected in Kaneohe Bay, Oahu, Hawaii. They were observed in the laboratory for a brief period. They were found to be non-gregarious and primarily nocturnal. It was possible to study feeding and defensive behavior. The species seems to prefer shrimps as prey. It is often cryptic. Among the adaptations for crypsis are color changes to match backgrounds (substrates), sand burrowing, and the cementing of sand grains to the back of an individual itself. The grains presumably are held in place by adhesive secretions of the skin. The captive animals also produced patterns which were conspicuous rather than cryptic. They were highly visible, occasionally intricate, combinations of light and dark. Some of them were distinctive. A single copulation was peculiar in certain respects (the spatial positions of the performers), but reminiscent of true cuttlefishes of the genus Sepia in other respects (color displays of both male and female). The phylogenetic implications of these observations are far from clear. On the behavioral evidence, Euprymna could be either a squid-like cuttlefish or a cuttlefish-like squid. It does not show any particular resemblance to Idiosepius, another supposed relative of Sepia.

Group Sizes of Antelopes in an East African National Park

Abstract: [Bei 11 Transektzahlungen entlang der Strasen und Wege im Nakuru Nationalpark, Kenya, wurde die Grose und Zusammensetzung jeder Antilopengruppe registriert. Die Haufigkeitsverteilung der Gruppengrosen von acht Antilopenarten (4430 Gruppen) wird beschrieben. Schoslingsfresser hatten niedrigere Gruppengrosen als Grasfresser; mittlere und maximale Gruppengrose waren positiv korreliert mit der Korpergrose der Art; Arten, die in offenem Grasland lebten, kamen in groseren Gruppen vor als Arten, die in dichterer Vegetation lebten. Die Messungen stimmen also gut mit den Hypothesen von JARMAN (1974) und ESTES (1974) uberein. Zusatzlich wurde gezeigt, das die durchschnittlich pro Monat gezahlte Zahl der Tiere pro Art und die Gruppengrose positiv korreliert waren. Die Kausalfaktoren, die die gefundenen Korrelationen verursacht haben konnten, werden diskutiert.Summary During 11 road strip counts in Lake Nakuru National Park, Kenya, the size of every antelope group encountered was recorded. The frequency distribution of group sizes of the eight most common species (steenbok, Kirk's dikdik, bushbuck, bohor reedbuck, mountain reedbuck, Thomson's gazelle, impala, waterbuck) is described. The data agree well with JARMAN'S (1974) hypothesis, which relates feeding style, body size, and group size, and with ESTES' (1974) hypothesis, which relates habitat structure and group size: browsers had lower group sizes than grazers, group size was positively correlated with body weight of the species, and species living in open grassland had larger group sizes than those living in dense vegetation. In addition, the average and maximum group size of the eight species was positively correlated with the average number counted per month, Bei 11 Transektzahlungen entlang der Strasen und Wege im Nakuru Nationalpark, Kenya, wurde die Grose und Zusammensetzung jeder Antilopengruppe registriert. Die Haufigkeitsverteilung der Gruppengrosen von acht Antilopenarten (4430 Gruppen) wird beschrieben. Schoslingsfresser hatten niedrigere Gruppengrosen als Grasfresser; mittlere und maximale Gruppengrose waren positiv korreliert mit der Korpergrose der Art; Arten, die in offenem Grasland lebten, kamen in groseren Gruppen vor als Arten, die in dichterer Vegetation lebten. Die Messungen stimmen also gut mit den Hypothesen von JARMAN (1974) und ESTES (1974) uberein. Zusatzlich wurde gezeigt, das die durchschnittlich pro Monat gezahlte Zahl der Tiere pro Art und die Gruppengrose positiv korreliert waren. Die Kausalfaktoren, die die gefundenen Korrelationen verursacht haben konnten, werden diskutiert.Summary During 11 road strip counts in Lake Nakuru National Park, Kenya, the size of every antelope group encountered was recorded. The frequency distribution of group sizes of the eight most common species (steenbok, Kirk's dikdik, bushbuck, bohor reedbuck, mountain reedbuck, Thomson's gazelle, impala, waterbuck) is described. The data agree well with JARMAN'S (1974) hypothesis, which relates feeding style, body size, and group size, and with ESTES' (1974) hypothesis, which relates habitat structure and group size: browsers had lower group sizes than grazers, group size was positively correlated with body weight of the species, and species living in open grassland had larger group sizes than those living in dense vegetation. In addition, the average and maximum group size of the eight species was positively correlated with the average number counted per month]

The Slave-Making Ant, Harpagoxenus Canadensis M. R. Smith, and Its Host-Species, Leptothorax Muscorum (Nylander): Slave Raiding and Territoriality

Abstract: The territorial hypothesis suggests that slave raiding in ants evolved from the territorial behaviour of free-living ancestors. In this study, the slave raiding behaviour of Harpagoxenus canadensis was observed and compared to the territorial behaviour of its host species, Leptothorax muscorum. Under laboratory conditions, colonies of both species attack and raid nearby L. muscorum nests, and display very similar raiding behaviours. At the conclusion of their raids, both species appropriate brood from raided nests. However, H. canadensis colonies rear the captured brood to produce slave workers, while L. muscorum colonies mutilate it and feed it to their larvae. In H. canadensis colonies, slaves join with the slave-makers in all aspects of raiding activity; and the differential treatment of captured brood was the only major difference we observed between the behaviour of enslaved and unenslaved L. muscorum workers. During interactions between colonies, workers of both species explore laboratory arenas ("scouting"), and attack alien members of either species that they encounter. Nonetheless, H. canadensis workers are markedly superior to L. muscorum in their fighting abilities, and consequently their colonies are capable of conducting successful raids against much larger host-species colonies. Workers of both species recruit nestmates to the scene of fights by leading tandem runs ("alarm-recruitment"); a behaviour which is typical of the territorial behaviour of various ant species. However, the discovery of such recruitment in H. canadensis is remarkable because all other known obligatory Lep- tothoracine slave-makers recruit nestmates during their slave raids only after they discover the target-colony's nest, and thereafter only lead recruitment to the target nest itself. These more specialized forms of slave-raid recruitment occur in an aggressive inter- colonial context virtually identical to that of alarm-recruitment and could easily have evolved from the alarm-recruitment of free-living ancestors. Tandem-run recruitment also occurred during the transport of captured brood following raids by colonies of either species. However, the context of this recruitment was quite different from that performed during the early stages of raids. Since H. canadensis colonies rear captured brood, this recruitment may be analogous to that led during emigrations to new nest sites ("transport-recruitment"). However, for L. muscorum colonies, this recruitment might be more properly considered as analogous to that led to food sources ("food-recruitment"). The results of this study demonstrate that all of the major elements which comprise the slave raids of H. canadensis and other Leptothoracine slave-makers occur during the apparently opportunistic, territorial raids of L. muscorum, and implicate such territorial behaviour as the proximate ancestor to slave raiding in this group of ants. The relatively minor differences which do occur can be regarded as specializations for slave-making. Since H. canadensis retains alarm-recruitment as a means of slave-raid recruitment, its slave raids can be regarded as the most primitive in the genus Harpagoxenus; and relatively more primitive than those of any other known obligatory Leptothoracine slave-maker.

Hormonal Induction of the Aquatic Phonotactic Response of Xenopus by

Abstract: Une reponse phonotactique a ete induite avec des X. laevis femelles en utilisant du gonadotopin chorionique de provenance humaine. Il s'ensuivait un mouvement delibere et caracteristique vers un haut-parleur place dans l'eau qui diffusait des appels nuptiaux conspecifiques. Les mâles, en appelant detectent d'autres grenouilles pres d'eux par des effets de compression dans l'eau. On a remarque une variabilite dans l'intensite de la reponse aux appels nuptiaux chez les femelles traitees avec l'hormone. Environ 52% des femelles produisant une reponse phonotactique positive ont aussi montre un comportement mâle. Lorsqu'elles furent presentees avec des appels nuptiaux de X. laevis melangees avec ceux de X. muelleri, les X. laevis femelles ne reagissaient qu'aux appels conspecifiques. Ces appels different dans leurs taux de pulsation et dans leur structure. L'habilite des femelles de X. laevis a reagir uniquement aux appels conspecifiques explique la rarete d'hybrides naturels dans les regions de sympatrie avec X. muelleri aussi que la facilite avec laquelle les hybrides sont obtenus au laboratoire, ou la fonction de l'appel nuptial est effectivement elimine.

Use of Perches as Vantage Points During Foraging By Male and Female Stonechats Saxicola Torquata

Abstract: The behaviour of individual stonechats (Saxicola torquata) foraging in heathland habitats was studied, to reveal possible influences of the height of the perches used as vantage points on feeding efficiency. Feeding rates, methods of prey capture, time spent on perches, and perching heights were quantified for male and female birds in a pre-breeding, and breeding periods; in addition, the integration of foraging with pre-breeding male song behaviour was examined. Rates of prey capture were highly variable, showing no clear seasonal trends or sex differences. Perching heights averaged 1.0 m in spring, and 1.6 m in summer, and although sex differences were small, males tended to perch higher, and closer to the top of the vegetation, in spring. Comparison with randomly encountered perches showed that birds selected higher perches than the average available. Of three principal prey-capture techniques, only diving to the ground was used in spring, but flycatching, and snatching prey off foliage, were also employed in summer. The change correlated with the appearance of new prey types on the foliage of birch and bracken. Visits to perches were short, averaging 25 s, and showed no clear sex or seasonal differences, but tended to be longer on higher perches, up to 2 min. These data were combined to assess the profitabilty for foraging of different perching heights. For feeding by diving to the ground, the lowest heights provided the greatest capture rates, but for flycatching and snatching, very high perches were more successful. The birds' observed preferences for perches in spring corresponded to those allowing the highest chance of capture per visit, rather than per unit time. In summer, there was no correspondence. Birds departed from perches when their prospects of capture were still high, and thus the lengths of unsuccessful visits cannot be regarded as 'giving-up' times. In spring, the frequencies of foraging attempts and song-phrases were inversely related in short observation periods, and incompatibility of the activities was suggested by the different heights chosen (averaging 0.9 m for foraging, 1.8 m for singing). The lack of differences in the spring foraging behaviour of males and females (who do not sing) suggests that males separated their foraging and singing into discrete bouts. This was apparently accomplished by tactical allocation of time in stable conditions, rather than relegation of singing to times when foraging conditions were poor.