Showing papers in "The Condor in 1990"
TL;DR: The spatial distribution of Red-tailed Hawks and Northern Harriers overwintering in central Arkansas was studied in relation to perch availability, plant cover, and small rodent biomass in six habitat patch types to interpret the general distribution as a response to prey biomass availability.
Abstract: The spatial distribution of Red-tailed Hawks (Buteojamaicensis) and Northern Harriers (Circus cyaneus) overwintering in central Arkansas was studied in relation to perch availability, plant cover, and small rodent biomass in six habitat patch types. In general, raptor foraging was distributed nonrandomly among patch types. Red-tailed Hawks occupied corn stubble and old-field patches more frequently than expected by chance and occupied tall corn and bare patches less frequently than expected. Adult male Northern Harriers used corn stubble and wetland patches more frequently than expected and used tall corn and bare patches less frequently than expected, while adult female and juvenile harriers used wetland patches more frequently than expected and used bare patches less frequently than expected. The general distribution of Northern Harriers is interpreted as a response to prey biomass availability (rodent biomass index x 1/plant cover density), while Red-tailed Hawk distribution is interpreted as a response to both prey biomass availability and perch availability.
175 citations
TL;DR: It is suggested hat avian color preferences may not provide strong selection favoring the evolution of the common fruit colors, and that the frequency distribution of fruit hues is best explained in other ways.
Abstract: Aviary experiments demonstrated that three North American fmgivorous migrant bird species often exhibit color preferences, when factors such as taste, nutrition, and accessibility to food sources are equal. Individual birds differed in initial color preferences, transitivity, and temporal stability of color preferences. There was little tendency of these birds to favor red and black, which are the most common colors of fruits of bird-dispersed plants, and a weak tendency to reject yellow. We suggest hat avian color preferences may not provide strong selection favoring the evolution of the common fruit colors, and that the frequency distribution of fruit hues is best explained in other ways.
122 citations
TL;DR: Etude de l'habitat et du comportement alimentaire de 31 especes utilisant deux iles de la Napo River (Perou).
Abstract: Etude de l'habitat et du comportement alimentaire de 31 especes utilisant deux iles de la Napo River (Perou)
120 citations
115 citations
TL;DR: Stable carbon and nitrogen isotopic analyses of muscle tissue from Marbled Murrelets and nine other species of alcids from British Columbia and the high Arctic indicate that stablenitrogen isotope analysis is potentially useful for establishing trophic relationships in seabird communities.
Abstract: Stable carbon and nitrogen isotopic analyses were performed on tissues of 21 Marbled Murrelets (Brachyramphus marmoratus) collected in Barkley Sound (n = 18) and on Johnston Lake, British Columbia (n = 3). Three adult males had significantly lower muscle tissue 613C values (x ? SD: -23 ? 2.7%0, n = 3) than did all other murrelets (16.5 ? 0.6%0, n = 18). Based on a model predicting muscle 6'3C values for murrelets feeding on freshwater and marine prey these three individuals had short-term freshwater-derived protein inputs to their diets ranging from 50 to 100%. The mean 613C value for Marbled Murrelet bone collagen (-16.8 ? 0.3%0, n = 4) was not significantly different from that found for Ancient Murrelets (Synthliboramphus antiquus) from Reef Island, Queen Charlotte Islands. This suggests that while some Marbled Murrelets may feed exclusively on freshwater prey for a short but important period of several weeks, freshwater protein is not a significant long-term dietary component in their diets. Marbled Murrelets had a mean muscle s5N value of 15.3 ? 0.7%0 (n = 21). Because 6' N values for freshwater and marine prey species overlapped significantly, stable-nitrogen isotope analysis did not distinguish between Marbled Murrelets feeding on freshwater or marine prey. The stable-nitrogen isotope values of muscle tissue from Marbled Murrelets were compared with those of nine other species of alcids from British Columbia and the high Arctic. The comparison indicates that stablenitrogen isotope analysis is potentially useful for establishing trophic relationships in seabird communities.
111 citations
TL;DR: There were significant differences in habitat structure (e.g., canopy closure, shrub cover, herb cover, old-growth conifer basal area, and hardwood tree density) among habitats used for frequent foraging, infrequent foraging and roosting in Northern Spotted Owls.
Abstract: We studied the summer habitat ecology of 12 Northern Spotted Owls (Strix occidentalis caurina) in two areas of northwestern California. Spotted Owls used mature or old-growth conifer forests significantly more than expected relative to their availability within their home ranges. In contrast, Spotted Owls used forests of intermediate and young age significantly less than expected relative to their availability within their home ranges. Eighty four percent of 616 Spotted Owl radiotelemetry locations were recorded in mature or old-growth forests. Spotted Owls used forests of complex structure and old age. There were significant differences in habitat structure (e.g., canopy closure, shrub cover, herb cover, old-growth conifer basal area, and hardwood tree density) among habitats used for frequent foraging, infrequent foraging, and roosting. In addition, male and female owls appeared to select habitats with different structure for foraging. Male owls which are smaller than female owls foraged in habitats which had higher tree density than female owls. The mean summer home-range size was 413 ha (SD = ?+196 ha) with males having smaller mean home-range size than females (338 ha and 538 ha, respectively).
106 citations
TL;DR: The hypothesis that sugar preferences and nectar composition are correlated with differences in the efficiency with which hummingbirds assimilated different sugars and/or in the time they required to process these sugars in the digestive system was tested.
Abstract: The nectar secreted by hummingbird-pollinated flowers is rich in sucrose, whereas nectar secreted by passerine-pollinated plants contains a mixture of glucose and fructose. To test the hypothesis that sugar preferences and nectar composition are correlated, I examined the sugar preferences of three species of Mexican hummingbirds (Amazilia rutila, Cynanthus latirostris, and Chlorostilbon canivetiz]. As predicted, the three species preferred sucrose over glucose, fructose, and a mixture of glucose and fructose (hexose mixture) in paired preference tests. Preferences for simple sugars were ranked as: sucrose > hexose mixture > glucose > fructose. The preference of hummingbirds for sucrose was not reversed by feeding hummingbirds a hexose mixture as a sole diet for 20 days. The preferences of hummingbirds for different sugars are puzzling because sucrose, glucose, and fructose have approximately the same energetic content. I hypothesized that sugar preferences were correlated with differences in the efficiency with which hummingbirds assimilated different sugars and/or in the time they required to process these sugars in the digestive system. Sucrose, glucose, and fructose, however, were assimilated by hummingbirds with equally high efficiency (> 97%). Glucose solutions were processed by hummingbirds at a slower rate than hexose mixtures and sucrose solutions, and hence, were less profitable. Sucrose and hexose mixtures were processed at the same rate and therefore had the same profitability. Therefore, the preference of hummingbirds for sucrose over hexose mixtures cannot be explained by differences in assimilation efficiency or digestive handling time. Sucrose must be hydrolyzed into its monosaccharide components, glucose and fructose, before it can be absorbed in the intestine and used as an energy source. Relative to other birds, hummingbirds exhibit highly specialized digestive traits, such as very high rates of intestinal sucrose hydrolysis and glucose transport, which allow them to use sucrose as efficiently as mixtures of glucose and fructose. Many passerine species, in contrast, use the more easily absorbed monosaccharides, glucose and fructose, more efficiently than sucrose. The distribution of nectar sugars among bird-pollinated plants seems to be the result of the evolutionary response of plants to two sets of pollinators with different degrees of digestive specialization.
104 citations
TL;DR: It is concluded that TOBEC provides an accurate estimate of total body fat, that it is preferable to traditional methods because it does not require sacrificing the bird, measurements can be taken quickly in the field, and (most importantly to field ornithologists) body fat can now be tracked through time for individual, free-living birds.
Abstract: Traditional methods to determine total body fat are undesirable under many circumstances because they require sacrificing individual birds. Walsberg (1988) recently introduced the total body electrical conductivity (TOBEC) method for total body fat to ecological studies. In this paper we expand on Walsberg's (1988) seminal paper and show that: (1) TOBEC is accurate under a narrow array of body masses, and is therefore appropriate for intraspecific studies; (2) dead birds exhibit significantly different TOBEC than live birds; and (3) the use of metal bands does not affect TOBEC measurements. We conclude that TOBEC provides an accurate estimate of total body fat, that it is preferable to traditional methods because it does not require sacrificing the bird, measurements can be taken quickly in the field, and (most importantly to field ornithologists) body fat can now be tracked through time for individual, free-living birds.
99 citations
TL;DR: Overall, fat scoring is described as a fairly precise method of indexing total body fat but with limited reliability among observers.
Abstract: Fat scoring is a widely used nondestructive method of assessing total body fat in birds. This method has not been rigorously investigated. We investigated interand intraobserver variability in scoring as well as the predictive ability of fat scoring using five species of passerines. Between-observer variation in scoring was variable and great at times. Observers did not consistently score species higher or lower relative to other observers nor did they always score birds with more total body fat higher. We found that within-observer variation was acceptable but was dependent on the species being scored. The precision of fat scoring was species-specific and for most species, fat scores accounted for less than 50% of the variation in true total body fat. Overall, we would describe fat scoring as a fairly precise method of indexing total body fat but with limited reliability among observers.
95 citations
TL;DR: Analysis of chickadee song revealed that fee declines in frequency in a glissando of nearly pure tone, then continues at greatly reduced amplitude at the start of bee; whereas bee is always lower in frequency than either the start or end offee.
Abstract: Black-capped Chickadee (Parus atricapillus) song consists of two notes, termed fee and bee. Frequency measures at three key points (at the start and end of fee, and at the start of bee) were obtained from the songs of a large sample of chickadees (n = 151) in the wild. In this sample, 19 birds produced songs shifted downward in frequency as well as their normal songs. Analysis of normal song revealed that fee declines in frequency in a glissando of nearly pure tone, then continues at greatly reduced amplitude at the start of bee; whereas bee, also a nearly pure tone, is always lower in frequency than either the start or end offee. The absolute pitches (frequencies) of these measures vary substantially among birds, but much less within individuals. In contrast, pitch intervals (ratios of higher to lower frequencies) for frequency changes among the three measures are highly invariant among birds. Moreover, chickadees with normal and frequency-shifted songs maintain virtually the same pitch intervals in both. This analysis suggests that the absolute and relative pitch constancies in chickadee song production may provide information for individual and species recognition, respectively.
91 citations
TL;DR: Two factors contribute to low growth efficiency: a slow growth rate, which may result in part from tannins contained in the nestling's partially acorn diet, and thermostatic costs associated with a low nest-cavity Ta.
Abstract: We used the doubly labeled water (DLW) technique to measure the field metabolic rate (FMR) of adult (n = 4) and nestling (n = 30) Acorn Woodpeckers (Melanerpes formicivorus). Resting metabolic rate (RMR) of adults and nestlings was calculated from 02 consumption. We constructed the nestlings' energy budget from measurements of the growth rate, FMR, and RMR of different aged nestlings. We measured the body temperature (Tb) of two nestlings in the field using implanted radiotelemeters, assessed the nestlings' thermal environment in terms of the air temperature (Tj experienced inside and outside of nest cavities, and studied the ontogeny of nestling homeothermy in the laboratory. Adult FMR averaged 195 kJ/day, which is 30% lower than predicted from adult mass (82 g) and 2.7 times the measured basal metabolic rate. Nestling FMR (kJ/day) increased with mass (m in grams) according to the relation: FMR = -27.1 + 2.4m. Nestling FMR stabilized at about 160 kJ/day (82% of the adult level) by 3 weeks of age. Nestlings, which are adult sized when they fledge 30-32 days after hatching, grow relatively slowly. Their logistic growth rate constant (K = 0.226) is 30% lower than predicted from their mass and is equivalent to that of a tropical species of their size. Nestlings also develop endothermy much more slowly than expected and are unable to maintain adult Tb when exposed to 150C for 30 min until they are 3 weeks old. In the field, nestling Tb fluctuated until about 3 weeks of age, apparently due to intermittent brooding by the adults. Nestlings metabolized an average of 3,853 kJ/bird over the nestling period (age: 0-31 days). Of the total, RMR comprised 46.8%, whereas activity, thermoregulation, and the heat increment of feeding combined accounted for 40.2%. The energy accumulated in growth amounted to 501 kJ, or 13% of the total. Gross growth efficiency (ratio of energy accumulated in tissue to total metabolized energy) is the lowest reported for any bird. Two factors contribute to low growth efficiency: (1) a slow growth rate, which may result in part from tannins contained in the nestling's partially acorn diet, and (2) thermostatic costs associated with a low nest-cavity Ta. These unusual physiological features indicate that energetic constraints may play an important role in influencing the costs and benefits of group living in this cooperatively breeding species.
TL;DR: In this article, a model was devised by which to explore the efficiency of metabolic usage of seeds by granivorous birds in meeting simultaneously their water and enegy needs, and the model was used to evaluate the water and energy efficiency of seeds.
Abstract: A model has been devised by which to explore the efficiency of metabolic usage of seeds by granivorous birds in meeting simultaneously their water and enegy needs
TL;DR: Differences between galbula and bullockii in the timing of the fall molts relative to the fall migration and in having or not having a prealternate molt may provide strong sources of selection against hybrids.
Abstract: We compare the molt and migration schedules of Baltimore (Icterus g. galbula) and Bullock's (I. g. bullockii) orioles, describe how bullockii and Black-backed Orioles (I. g. abeillei) in juvenile plumage can be distinguished, and present a simple quantitative character that serves to distinguish the juvenile and basic plumages of bullockii. Galbula undergoes the first and later prebasic molts on the breeding grounds, while bullockii in both juvenile and worn breeding plumage almost certainly migrate to the American southwest prior to undertaking the fall molts. This early migration by bullockii has probably been favored as a mechanism for them to escape the dry late summer conditions that prevail in most of their breeding range and to exploit for molting the food flush caused by the late summer monsoon rains in the southwest. With but one exception, every bullockii specimen taken in late summer or fall south of the breeding range in Mexico was in fresh basic plumage. Thus, the fall migration of bullockii may be interrupted for the prebasic molts. Bullockii almost entirely lacks a prealternate molt in all sex and age classes. The prealternate molt in galbula is fairly extensive in first-year males but limited in females and in older males. First year galbula males initiate this molt in their throat in early winter, perhaps to acquire a badge that helps distinguish them from first-year females, which have light throats, and from those older females that have light throats. Some galbula males that are almost a year old also undergo part of the prealternate molt after their arrival on the breeding grounds. Implications of these observations for theories of subadult plumages are discussed. These differences between galbula and bullockii in the timing of the fall molts relative to the fall migration and in having or not having a prealternate molt may provide strong sources of selection against hybrids. One specimen illustrating some of the potentially deleterious recombinations of molt and migration schedules among hybrids is described in detail.
TL;DR: A travers l'etude des deplacements de greves des bois sedentaires ou nomades, hivernant dans la region de Veracruz au Mexique, l'auteur examine le role de la territorialite dans the regulation de la population.
Abstract: A travers l'etude des deplacements de greves des bois sedentaires ou nomades, hivernant dans la region de Veracruz au Mexique, l'auteur examine le role de la territorialite dans la regulation de la population
TL;DR: In this paper, the authors determined bird species densities for summer and winter on 132 study plots grouped into 25 riparian habitats in or near the Huachuca Mountains of southeastern Arizona.
Abstract: Bird species densities were determined for summer and winter on 132 study plots grouped into 25 riparian habitats in or near the Huachuca Mountains of southeastern Arizona. The habitats were defined based on the dominant riparian tree species, the size of the riparian stand, and the type of adjacent upland vegetation. Vegetation characteristics and physical environmental data were collected at each plot. The type of dominant riparian tree species influenced bird species richness and total density during the breeding season. Cottonwood habitats had the greatest richness, and both cottonwood and sycamore habitats had high densities. Upland vegetation was an important factor related to winter species richness and abundance, with plots in open grassland areas having greater richness and density. Riparian stand size was a relatively poor predictor of avian density or richness in either season. Groups of bird species that shared similar density distributions in the summer were associated with specific riparian habitats. The winter pattern of species groups was not as clear, and groups could not be assigned to riparian habitats, but they were related to either wooded or open upland vegetation. Riparian habitats were also clustered based on similar densities of birds. In summer, high-elevation habitats were distinct from low-elevation and foothill habitats. In winter, riparian habitats separated into categories of wooded vs. open adjacent vegetation.
TL;DR: Investigation of defensive behavior of American Redstarts in response to models of a female Brown-headed Cowbird and a control placed near their nests found that redstarts are more familiar with cowbirds in fragmented landscapes because cowbirds are more common there and pose a greater threat to this host's reproductive success.
Abstract: Defensive behavior of American Redstarts (Setophaga ruticilla) in response to models of a female Brown-headed Cowbird (Molothrus ater) and a control (Spizella passerina, Passerella iliaca, or Melospiza melodia) placed near their nests was investigated in fragmented and contiguous boreal forest of western Canada. Female redstarts usually discovered and responded first to models but males also participated in nest defense. Based upon several behavioral measures, which included distraction displays, close passes or strihng the model, and alarm \"chip\" or \"buzz\" vocalizations, female redstarts reacted more intensely or aggressively to the cowbird model in fragmented compared with contiguous forested landscapes. We interpret these differences as evidence that redstarts are more familiar with cowbirds in fragmented landscapes because cowbirds are more common there and pose a greater threat to this host's reproductive success. Our findings have implications for interpretations of the demography of redstart populations and the fixation of antiparasite behavioral responses within populations. We suggest that tests using models provide a viable means of evaluating the influence of landscape matrix on the severity of cowbird exposure to host populations.
TL;DR: Les objectifs de l'etude sont de determiner le nombre relatif de chaque espece utilisant cette region and de decrire les aspects temporels and spatiaux de leur presence.
Abstract: Les objectifs de l'etude sont de determiner le nombre relatif de chaque espece utilisant cette region et de decrire les aspects temporels et spatiaux de leur presence
TL;DR: According to this study, increased oxygen demands in winter-acclimatized Dark-eyed Juncos are met, in part, by increased oxygen carrying capacity, but not by decreased oxygen affinity.
Abstract: Small birds wintering in temperate climates must increase rates of aerobic metabolism to meet thermoregulatory demands. Increased oxygen delivery to the tissues and/or increased oxygen unloading at the tissues may be involved in meeting this need. This study examines seasonal variation in vascular oxygen transport of Dark-eyed Juncos (Junco hyemalis) in western Oregon. Oxygen dissociation curves, hematocrits, and oxygen carrying capacities were determined in summerand winter-acclimatized juncos. Oxygen affinity did not vary seasonally, Pso values for summer and winter were 54.1 torr and 54.0 torr, respectively, at 4 1C and pH 7.5. Hematocrit values averaged 47.2 ? 3.3% in summer and 52.6 ? 2.0% in winter and were significantly different. Mean values for oxygen carrying capacity, 13.33 ? 1.21 vol % in summer and 14.48 ? 1.20 vol % in winter, also differed significantly. Apparently, increased oxygen demands in winter-acclimatized Dark-eyed Juncos are met, in part, by increased oxygen carrying capacity, but not by decreased oxygen affinity.
TL;DR: Correlations were found between feeding visits by some groups of birds and percent water in the pulp, milligrams of mineral ash in the timber, and crop size, suggesting that the correlation with crop size may represent a tactic to minimize predation.
Abstract: The rates at which birds visit fruiting individuals of Allophylus edulis (Sapindaceae) differ substantially among trees. Such avian feeding preferences are well-known, but usually involve fruits and trees of different species. Factors controlling avian preferences for particular trees in a population of conspecifics are generally undocumented. To address this issue, I attempted to correlate rates at which individuals birds and species fed in trees of A1ZophyZu.s with 27 fruit or plant characteristics. Birds that swallow fruits whole were considered separately from those that feed in other ways. Plant characters were selected on the basis of their potential influence on feeding efficiency or predation risk, assuming that birds would select feeding trees so as to maximize the net rate of energy or nutrient intake and to minimize predation. Correlations were found between feeding visits by some groups of birds and percent water in the pulp, milligrams of mineral ash in the pulp, and crop size. No character was correlated with feeding visits by all groups of birds in both years of the study. The correlations with water and mineral ash are unexplained and may be artifacts. The correlation with crop size may represent a tactic to minimize predation.
TL;DR: In this paper, the authors describe du repertoire sonore de la chouette tachetee and influence of quelques facteurs environnementaux (conditions meteorologiques et phases lunaires) sur le comportement vocal.
Abstract: Description du repertoire sonore de la chouette tachetee et influence de quelques facteurs environnementaux (conditions meteorologiques et phases lunaires) sur le comportement vocal
TL;DR: It was observed that yearling males tended in all comparison intervals to have lower body masses, shorter wings, and shorter testis and cloacal protuberance lengths than older males--they were smaller birds, while older males were also less successful in obtaining mates but, once paired, reared just as many offspring.
Abstract: Plasma levels of testosterone (T) were measured by radioimmunoassay in Mountain White-crowned Sparrow (Zonotrichia leucophrys oriantha) males of known age and natural history during four consecutive reproductive seasons in the Sierra Nevada of California. Because nesting occurred comparatively early in all of these seasons and mean schedules varied by only 11 days, data were lumped to show the seasonal pattern of T. This pattern was unimodal with a maximum coinciding with the period of competition for territories and mates and with mate guarding. This was followed by a decrease toward a minimum that coincided with the period of parental care and, eventually, postnuptial molt. When these data were analyzed by stage of the reproductive season (rather than calendar date) and by age, two unexpected results emerged. First, T levels decreased significantly between the stages of nest building and laying. Female mates should have been fertilizable and soliciting copulations during both of these stages and intermale conflicts associated with mate guarding should have been frequent. In both situations, high T levels would be predicted by current paradigms. Second, T levels were considerably lower in yearling males than in older males prior to the laying stage. Reasons for this age-related difference are unknown but it was observed that yearling males tended in all comparison intervals to have lower body masses, shorter wings, and shorter testis and cloacal protuberance lengths than older males--they were smaller birds. Yearling males were also less successful in obtaining mates than older males but, once paired, reared just as many offspring.
TL;DR: The prevalence of lead in Golden Eagles (Aquila chrysaetos) occurring within the recent historical range of the California Condor (Gymnogyps californianus) was deter- mined by analyzing blood samples from 162 Golden Eagles captured between June 1985 and December 1986 at three sites as discussed by the authors.
Abstract: The prevalence of lead in Golden Eagles (Aquila chrysaetos) occurring within the recent historical range of the California Condor (Gymnogyps californianus) was deter- mined by analyzing blood samples from 162 Golden Eagles captured between June 1985 and December 1986 at three sites. We found no significant differences between sex and age classes in blood lead levels nor were there differences between residents and migrants. Significant differences were found between months with the highest blood lead levels oc- curring during the fall/winter period. Approximately one-third (35.8%) of the Golden Eagle population sampled had elevated blood lead levels, values similar to those reported for free- flying California Condors. Given this rate of exposure, if the proposed releases of California Condors back to the wild are to succeed, whether in their former range or elsewhere, any potential for lead poisoning must be reduced. It is essential that we identify the sources of the lead, the seasonal and geographic distribution of these sources, and develop management strategies to reduce or eliminate the hazard.
TL;DR: Nesting data on a marked known-age population of Wrentits in central coastal California revealed that 20% of the breeding pairs during the 4 years 1982-1985 attempted a second brood after successfully fledging young from an earlier brood.
Abstract: The Wrentit (Chamaea fascia@ has been reported to raise only one brood per year. Nesting data on a marked known-age population of Wrentits in central coastal California revealed that 20% of the breeding pairs during the 4 years 1982-1985 attempted a second brood after successfully fledging young from an earlier brood. The probability of a pair attempting a double brood significantly decreased the later the first clutch was completed. No second broods were attempted if the first clutch was completed later than 5 May (14% of breeding pairs) or if the first attempt failed (4 1%). The remaining pairs (24%) attempted only one brood although they appeared to have the opportunity to attempt two broods. Adults attempting a second brood reduced the amount of postfledging care given to the young of the previous brood. Double-brooding individuals tended to be older, have better nest survivorship, and fledged significantly more young per season than single-brooding individuals. Survival of the adults to the next breeding season was independent ofthe number of broods attempted. Young males had significantly lower nest success than older males and young females began nesting significantly later than older females, which may explain the lower incidence of double brooding in young birds.
TL;DR: Based on the range of CVs observed among species in this study, the number of sample plots needed to detect a statistical difference in density of a given species between samples is probably prohibitive and practitioners need to design studies to control observer and analyst variability.
Abstract: We studied variation in density estimates from spot mapping that was attributable to analysts and observers, using expert birders with little or no prior experience with spot mapping. Three observers independently spot mapped one 42-ha plot (Markwood) in mixed-conifer forest, and four others independently spot mapped another (Teakettle). All observers analyzed all maps. Consistency among analysts and observers in estimating the numbers of territories of breeding species on each plot was generally poor. Across all combinations of analysts and maps, 71% of all ANOVAs had significant analyst and/or observer effects. Observer effects were generally greater than analyst effects. When observers analyzed their own species maps, CVs of individual species ranged from 0% to 173% (mean 41%) at Markwood and from 0% to 188% (mean 60%) at Teakettle. As in similar studies, mean CVs from pooled totals of all species were less than those from individual species and were within the range of variation found by other researchers. Based on the range of CVs observed among species in this study, the number of sample plots needed to detect a statistical difference in density of a given species between samples is probably prohibitive for most studies. Instead, practitioners need to design studies to control observer and analyst variability.
TL;DR: Discussion sur les implications ontogenetiques, ecologiques, taxonomiques and pour l'evolution, de l'absence d'aile chez la sarcelle des iles Auckland.
Abstract: Analyses morphometriques et descriptions qualitatives d'echantillons de peau et de squelettes et etudes de dissections myologiques d'appendices pectoraux.Discussion sur les implications ontogenetiques, ecologiques, taxonomiques et pour l'evolution, de l'absence d'aile chez la sarcelle des iles Auckland.
TL;DR: Autumn foraging flocks of European Starlings (Sturnus vulgaris) foraging on grass lawns were studied to determine how flock size and position within the flock affect the birds' foraging behavior.
Abstract: We studied autumn foraging flocks of European Starlings (Sturnus vulgaris) foraging on grass lawns to determine how flock size (up to ca. 250 individuals) and position within the flock (edge vs. center) affect the birds' foraging behavior. The birds fed exclusively by probing their bills into the ground, gaping, and extracting beetle larvae or earthworms, which were directly observed by us. Neither flock size nor position affected the rate of prey capture. Edge birds, however, spent more time vigilant and probed less than center birds. Rates ofagonistic interactions did not differ between flock positions; therefore, the percentage of time actually spent foraging (i.e., walking, searching, and probing) was lower for edge birds due to their higher level of vigilance. The only behaviors affected by flock size were percentage of time spent vigilant and percentage of time spent foraging, but only for edge birds in flocks of 520 individuals. The rate of agonistic interactions did not increase with increasing flock size for edge or center birds. Probe rate was not correlated with prey capture rate, placing caution on indiscriminate use of probe (or peck) rate as an index of prey capture rate. The likely nature of the dispersion pattern of the starling's prey is discussed in relation to our results.
TL;DR: It is suggested that first-time breeders are slightly less efficient at feeding the chick than experienced birds, but they attain similar skills within a few months, and pairs do not increase their efficiency after a first fledging attempt.
Abstract: The growth of the chicks and pattern of feeds to the chicks were studied for Wandering Albatross pairs (Diomedea exulans) with (1) no previous breeding experience, (2) a limited experience, and (3) an extensive experience. Chicks of inexperienced pairs grew more slowly than those of experienced pairs only during the first part of the fledging period and they had similar dimensions and weights when they left the colony. These differences resulted from different patterns of food delivery to the chicks during the first part of the fledging period; chicks of inexperienced pairs being fed less regularly but with larger meals than those of experienced pairs. The patterns of chick feedings were similar in the two categories during the second part of the fledging period. There was no difference between the feeding patterns for chicks of pairs with either an extensive or a limited experience and small differences in growth appeared only during the first weeks of life of the chicks, probably because of differences in egg size. These results suggest that first-time breeders are slightly less efficient at feeding the chick than experienced birds, but they attain similar skills within a few months, and pairs do not increase their efficiency after a first fledging attempt.
TL;DR: The behavior of Ad6lie Penguins, Pygoscelis adeliae, was investigated near Syowa Station during December 1986, with time-depth recorders attached to nesting birds caring for 2to 3-week-old chicks as discussed by the authors.
Abstract: The diving behavior of Ad6lie Penguins, Pygoscelis adeliae, was investigated near Syowa Station during December 1986, with time-depth recorders attached to nesting birds caring for 2to 3-week-old chicks. Three of four recorders were recovered 150-334 hr after attachment. Most (98%) of the 587 dives recorded were less than 20 m in depth and 40% occurred between 16:00 and 20:00. Mean depths ranged from 6.1-10.9 m and maximum depth was 16.9-26.8 m. Mean and maximum dive durations were 1.4-1.9 min and 2.7-4.0 min. Ninety-seven percent of dives occurred in 44 diving bouts that averaged 25.3 min and 12.9 dives per bout. Descent and ascent rates during dives were similar in 88% of dives, meaning that the penguins dived at low angles, averaging 5*.