Showing papers in "Ibis in 1994"

Incubation routine, body mass regulation and egg neglect in the Blue Petrel Halobaena caerulea

Abstract: The incubation routine and mass changes of male and female Blue Petrel Halobaena caerulea were studied at the Kerguelen Islands to investigate factors influencing the durations of incubation stints and foraging trips at sea and the factors determining nest desertion and return to the nest. The body mass at the start of an incubation shift and also when the bird was relieved varied throughout the incubation period, whereas the mass when birds deserted the nest was stable. Birds deserted the nest when their mass decreased to threshold, independent of the duration of the fast. Temporary egg neglect was observed in successful as well as in unsuccessful breeding attempts, but it increased the risk of breeding failure. The net and daily massgained at sea during the second part of the incubation period were higher than during the first part, suggesting an increase in food availability. During the first part, the mass gained at sea and time spent foraging were inversely related to the mass of the bird before it left the burrow, whereas a similar relationship did not occur thereafter. The results suggest the occurrence of a fixed mass threshold when birds decide to leave the nest if not relieved by their partner. The mass when a bird left its nest inffuenced the time spent foraging or mass gained when food was scarce. Although decision rules to leave the nest or return from the sea are related to body condition. the possibility of neglecting the eggs temporarily enables Blue Petrels to regulate the trade-off between risks of breeding failure and risks of an increase in adult mortality. A model for behavioural decision to stop incubating or stop feeding, based on a variable set point, is proposed.

Determination of clutch-size in the Kentish Plover Charadrius alexandrinus

Abstract: We studied the clutch-size distribution of Kentish Plover Charadrius alexandrinus in 1991 and 1992 and tested three hypotheses for determination of clutch-size: egg-formation ability of females, incubation ability of parents and nest predation. Variation in clutch-size was small: 71 out of 74 clutches had three eggs (coeff. var. = 7%). Females spent more time foraging (51 ± 6%) pre-laying and during egg-laying than their mates (39 ± 5%). However, we concluded that egg-formation was not constrained by food availability because 77% and 100% of clutches were initiated before the peaks of prey density and of prey mass, respectively. Furthermore, the number of clutches initiated and completed over time was unrelated to prey density. By experimentally reducing and enlarging clutches, we found that enlarged clutches of four eggs took longer to hatch (24.8 ± 0.9 days) than control clutches of three (21.6 ± 0.7 days). Eggs of enlarged clutches also lost weight more slowly during incubation in both years compared with control clutches. No difference was found in the incubation behaviour or weight loss of parents between reduced, control and enlarged clutches. We found no evidence to support the nest predation hypothesis, since neither the proportion of nests predated nor the number of chicks hatched was different between reduced, control and enlarged clutches. The results of this study are most consistent with the incubation ability hypothesis, although the parental ability hypothesis has remained untested.

Diet, prey-size selection and intake rates of Black-tailed Godwits Limosa limosa feeding on mudflats

Abstract: This paper describes aspects of the winter feeding ecology of Black-tailed Godwits Limosa limosa on an intertidal mudflat in the Tagus estuary, Portugal. Their diet consisted mainly of the bivalve mollusc Scrobicularia plana, which represented 88% of the ingested biomass. The remaining 12% was the worm Nereis diversicolor and, occasionally, the snail Hydrobia ulvae. Ingested Scrobicularia varied between 10 and 20 mm in length, and all size classes of Nereis present in the sediment, except those smaller than 20 mm, were preyed upon. A change in dietary composition occurred over the winter, probably in response to changes in the availability of Nereis and small Scrobicularia. Intake rates averaged 74.9 mg dry weight per minute, which corresponded to a net energy intake of 1.21 kJ per min.

The effects of daylength and testosterone on the initiation and progress of moult in Starlings Sturnus vulgaris

Abstract: The effects of daylength and of testosterone implants, before and after the beginning of moult, on the timing and rate of primary moult have been quantified. Female Starlings Sturnus vulgaris were moved from natural daylength in February to 13 h or 18 h of light per day (13L: 11D or 18L: 6D). Some of the birds on 18L: 6D were left on 18L: 6D throughout the experiment and others were transferred to 13L: 11D after 6 weeks, before moult had begun, or after 12 weeks, after moult had begun. Birds kept on 18L: 6D began to moult before birds kept on 13L: 11D, but the subsequent rate of moult was the same in both groups. A decrease in daylength before moult started slightly advanced the onset of moult. A decrease after moult had begun increased the speed of moult. Castrated male Starlings on 18L: 6D were given testosterone implants for different periods before or after the beginning of moult. Testosterone treatment which ended before moult would normally have started had little effect. Treatment extending beyond the normal start of moult considerably delayed or even prevented the onset of moult. Moult was arrested in birds which received testosterone after moult had begun. On removal of testosterone implants, moult began again from the point where it had stopped, but in some birds, all of the feathers which had been regrown recently were dropped again and regrown. These results are discussed in relation to the different patterns of moult seen amongst different species.

Variability and stochasticity of meal size and feeding frequency in the Little Sheanvater Puffinus assimilis

Abstract: The pattern of chick feeding in Little Shearwater Puffinus assimilis on Selvagem Grande was examined by weighing chicks at 4–h intervals throughout eight successive nights and daily for a further 11 days (19 days in all). Individual meals fed to chicks averaged 23.2 g (s.d. ±4.7) or 13.6% of adult mass. Mass increments over 24 h (NET) were linearly related to the sum of positive mass increments over 4–h intervals during the night (SUM) by the equation NET = 0.36SUM - 5.89 (r2= 0.60). Using this relationship, I estimated that over a period of 18 nights, a mean of 95% of chicks were fed each night, and the mean interval between feeds was 1.05 nights, with a maximum of three nights. There was no significant day-to-day variation in feeding rate. These results were not compatible with the prevalent idea that the purpose of large fat deposits in Procellariiformes is to tide chicks over periodic fasts resulting from poor feeding conditions. On average, chicks required 16 g of food per day to maintain constant mass and converted 33% of their intake of food above this requirement into biomass. Meal size and feeding frequency were independent of chick size and body condition (body-mass corrected for body-size), and the masses of food received by individual chicks each night varied in direct proportion to previous values. These results suggest that the rate of food supply to chicks was not regulated by adjustment according to chicks' nutritional requirements. To some extent, this supports the hypothesis that lipid accumulation among Procellariiformes is related to stochastic variation in food supply rate, resulting from an absence of regulation of feeding. However, feeding was not stochastic, in that adults tended to deliver consistent amounts of food to their chicks, and the pattern of feeding among even the worst-fed chicks was inconsistent with a need for large lipid stores based upon chance variation in food delivery.

Interrelationships between breeding frequency, timing and outcome in King Penguins Aptenodytes patagonicus: are King Penguins biennial breeders?

Abstract: King Penguin Aptenodytes patagonicus chick growth is interrupted by a winter fast which extends the length of the breeding cycle (laying to chick independence) to 14–16 months, so that continuous annual successful breeding appears to be impossible. The 3–month laying period imposes further constraints with respect to timing of breeding attempts in relation to the onset of fasting. By the frequent resighting of individually marked birds at Marion Island, we examined the frequency of breeding and the relationships between timing, outcome and frequency in the same and in consecutive years. A total of 3101 adult King Penguins were banded between 1984 and 1991, yielding continuous breeding histories spanning a maximum of 5 years. Most penguins attempted to breed in consecutive years, although the likelihood of taking a year off increased with the number of consecutive attempts. In any one season, about 19% of potentially breeding adults did not breed. Early breeders were more likely to succeed than late breeders and comprised 84% of breeding attempts of known timing. Successful birds in one season usually bred late in the following season, whereas failed attempts were usually followed by an early attempt. Non-breeding was more likely to occur after a successful outcome than a failed one, and after a year off 93% of birds bred early. It is incorrect to refer to the King Penguin as a biennial breeder.

Song mimicry and species associations of west African indigobirds Vidua with Quail‐finch Ortygospiza atricollis, Goldbreast Amandava subflava and Brown Twinspot Clytospiza monteiri

Abstract: The brood-parasitic indigobirds Vidua spp. mimic the songs of their foster species, which for many species of indigobirds are Lagonosticta firefinches. We report additional associations of indigobirds with estrildid finches in west Africa. Quail-finch Indigobirds Vidua nigeriae in northern Cameroon mimic the songs of Quail-finch Ortygospiza atricollis. Gold-breast Indigobirds Vidua raricola in Cameroon and Sierra Leone mimic the songs of Gold-breast Amandava subflava. Both indigobirds are distinct in male breeding plumage from other indigobirds. Also, a population of blue indigobirds Vidua sp. in Cameroon mimics the songs of Brown Twinspot Clytospiza monteiri. They are similar in colour and size to blue indigobirds associated with Dark Firefinch L. rubricata and Black-bellied Firefinch L. rara. Mouth patterns of fledged young Quail-finch Indigobirds and Goldbreast Indigobirds resemble those of their song-model and presumed foster species, but the mouth pattern of a fledged young associated with the Brown Twinspot mimic was not distinct from the mouth of young Black-bellied Firefinch. The field observations show associations of certain species of indigobirds with finches other than the firefinches. The results are consistent with mitochondrial DNA estimates of greater genetic similarity among indigobirds than among their foster species. The field observations support the hypothesis of evolutionary associations of the brood parasite and foster species by colonization with switching from one foster to another rather than by cospeciation.

Storage of stones by Jays Garrulus glandarius

Abstract: The aims of this study were to test whether or not Jays Garrulus glandarius store stones and, if so, to examine the conditions under which they store stones. By directly observing the behaviour of five captive jays that were housed individually in flight cages, we found that stones were stored only in the absence of food items or when food items were no longer available to store and that there was a strong preference for storing stones that resembled acorns in both size and appearance (in terms of colour, shape and smoothness of the surface) and were undamaged rather than heavily chipped. These results are discussed in terms of Tinbergen's classic ethological model in which animals respond selectively to certain key features and ignore other features of the stimulus.

Effects of male removal on the behaviour and reproductive success of female eastern bluebirds Sialia sialis

Abstract: We removed male Eastern Bluebirds Sialia sialis to examine the importance of male parental care and the behavioural responses of unaided females to loss of male assistance. Unaided females fed young significantly more than control females (females with male assistance) fed young, but young in experimental nests were fed significantly less frequently in total than young in control nests. Unaided females had significantly lower nesting success (fledged at least one young) than control females. At control nests, males defended the young more strongly than did their mates. Unaided females defended their young as strongly as control females. Unaided and control females spent the same amount of time brooding young, and there was no tradeoff between feeding and brooding young. Most early season experimental nests failed, but late in the season many unaided females were as successful as pairs. Unaided females were able to match the feeding rat'e in control broods at late nests but not at early nests, where control nestlings were fed at a higher rate. In our population, male bluebirds played an important role in provisioning young, and early in the season unaided females were unable to provide sufficient bod to raise any young to fledging.

Seasonal patterns of sperm storage in the Yellow‐headed Blackbird Xanthocephalus xanthocephalus

Abstract: The seasonal pattern of sperm storage was examined in a wild population of Yellow-headed Blackbirds Xanthocephalus xanthocephalus by collecting females at eight different stages of their breeding cycle. Sperm storage tubules (SSTs) were present in simiktr numbers throughout all stages of the breeding season, from arrival on the breeding grounds to departure for winter. In contrast, the size of SSTs varied enormously over the season, reaching maximum size just prior to clutch initiation, when SSTs were more than three times the length of those found in post-breeding birds. The amount of sperm stored also varied over the season, in parallel with the growth and regression of SSTs. Sperm were first observed in SSTs approximately 2–5 days before laying and increased rapidly in abundance until clutch initiation. The amount of sperm stored then decreased gradually during the egg-laying period so that by clutch completion approximately 70% of stored sperm had disappeared from the SSTs. The rapid seasonal development and subsequent regression of SSTs in the Yellow-headed Blackbird contrast sharply with the pattern found in domestic poultry, where the imposition of continuous laying regimes has; led to the maintenance of SSTs at maximum size for extended periods of time.

Breeding success of a Lesser Spotted Woodpecker Dendrocopos minor population

Abstract: We made intensive observations of 50 pairs of Lesser Spotted Woodpecker Dendrocopos minor in southern Sweden from 1989 to 1992. Between 7% and 22% of the pairs each year defended a territory but laid no eggs. Overall, 76% of the pairs laying eggs raised fledglings, but this proportion was only 33% in 1991 when the weather was cold and wet. The mean clutch size (5.9) and brood size (4.5) in successful nests did not vary significantly between years. Incubation time was 1 day longer in 1991 (11–12 days) than in 1990 and 1992 (10–11 days). Number of young fledged per nesting attempt (3.5) and per pair (2.7) in the population also varied significantly between years. The initiation of egg laying varied between years but coincided each year remarkably well with the date when oak came into leaf. Breeding success is discussed, and comparisons are made with other hole-nesting species.

Colonial breeding and nest predation in the Jackdaw Corvus monedula using old Black Woodpecker Dryocopus martius holes.

Abstract: Jackdaws Corvus monedula breeding in old holes of the Black Woodpecker Dryocopus martius were studied during 6 years in central Sweden. Of 131 breeding attempts, only 56% were successful. Nest predation caused 74% of the breeding failures. The most common predator was probably the Pine Marten Mattes mattes, as fresh hair was found in 42% of the nests whose contents had been predated. Predation risk of nest contents was not related to the height above ground, but it was significantly reduced with increasing colony size. Since Jackdaws are known to communally defend their nests, a likely explanation is that the Jackdaw benefits from group defence against predators. During the study, the number of breeding Jackdaw pairs in Black Woodpecker holes declined, probably linked with a recent increase in the numbers of Pine Martens in the area.

Time and energy budgets of breeding males and females in sandgrouse Pterocles species

Abstract: The investment of time and energy in reproduction by male and female sandgrouse (genus Pterocles) was studied. Energy expenditure was estimated using time budgets and laboratory measurements of metabolism. Female parental expenditure was greatest during laying and incubation. Females took the larger share of daytime incubation, which reduced their time available for foraging (3.6 h compared with 4.8 h for males). To remain in energy balance, they required a higher food intake rate than males (97 kJ/h compared with 79 kJ/h, respectively) and consequently were likely to lose condition during incubation. Male parental expenditure was greatest during chick-rearing, especially when the young were well grown but still dependent on the male for water. The role of males as water carriers increased their energy expenditure and decreased their time available for foraging. Males also took the greater share of time spent in vigilance on behalf of the young, which further reduced their foraging time (3.2 h compared with 4.9 h for females). To remain in energy balance, males with young required a higher intake rate than females (62 kJ/h compared with 44 kJ/h, respectively).

The Nene Branta sandvicensis Recovery Initiative : research against extinction

Abstract: Since 1960, about 2150 Hawaiian Geese or Nene Branta sandvicensis were reintroduced in Hawaii to supplement the remaining wild population of about 30 birds. These geese were released mostly in high mountain sanctuaries. These sites became unsuitable during prolonged drought and the few surviving birds were those which had moved away from the release sites. The geese that survived had moved to, or were released near, agricultural pasture land. About 600 Nene are currently living in the wild; numbers are declining on the island of Hawaii, stable on Maui and increasing on Kauai. Management priorities include enhancement of grasslands, predator control and maximizing genetic diversity. To enable the species to recover, management will probably have to be large scale, intensive and prolonged. Further released captive-bred or translocated Nene should have access to enhanced habitats after predators have been controlled.