Showing papers in "The Condor in 1987"
TL;DR: Both the optimal temperature for continuous exposure and the range of temperatures producing high survivorship differ among species, and the use of a "physiological zero" applicable to all species is not warranted.
Abstract: Avian eggs usually experience temperatures of 30 to 400C during the incubation period, but eggs often cool to much lower temperatures. Hyperthermia is less common. Passerines do not show higher incubation temperatures than other orders that have been studied extensively. Field measurements of incubation temperatures are usually lower than the optimal temperatures for development found in laboratory studies. Some species regulate egg temperatures closely throughout incubation; but in at least one penguin species, mean egg temperature increases and ranges of egg temperature decrease through the incubation period. Both the optimal temperature for continuous exposure and the range of temperatures producing high survivorship differ among species. Species also differ in their responses to temperature exposures of limited duration. Thus, the use of a "physiological zero" applicable to all species is not warranted. Penguins have both a lower optimum and a broader range of acceptable incubation temperatures than do other species studied. Age, duration, and temperature of exposure significantly affect survivorship. Hyperthermia is evidently more injurious to the developing embryo than is hypothermia. Resistance to cold exposure is a heritable trait, but the genetics and physiology of the response(s) are not known. For older embryos, the physiological effects of hyperthermia are similar to those of adult birds in terms of the organ systems that are first to fail. An estimate of thermal tolerance for short exposures in most species studied is 16 to 41 C and, for exposures lasting several hours, 36 to 390C.
655 citations
TL;DR: This work presents a variety of Approaches to Habitat Selection in Birds and concludes with a call for further investigation into the role of enrichment in the selection process.
Abstract: Introduction. Habitat Selection in Specific Bird Taxa. Habitat Selection in Specific Habitat Types. A Variety of Approaches to Habitat Selection in Birds.
352 citations
TL;DR: Results of experiments that test effects of nest appearance and placement on probability of nest predation are reported, indicating that any biases were consistent among sites and nest types.
Abstract: Nest predation is a primary cause of nesting mortality for many bird species (Skutch 1949, 1966; Nice 1957; Ricklefs 1969; Nilsson 1984). Food limitation and competition also can affect nesting success (see reviews in Martin 1986, 1987). However, the primary role of nest predation in nesting mortality suggests that it can be a strong agent of selection on bird species and assemblages; when nest predation differs among species, habitats, and areas, it can influence life history traits, habitat use, and population and community patterns (Duebbert and Kantrud 1974; Slagsvold 1982; Martin, unpubl.). Intensity of nest predation differs among groups of birds based on the nesting substrates and heights of their nests (Ricklefs 1969, Nilsson 1984), between island and mainland areas (Loiselle and Hoppes 1983, Savidge 1987), and among habitat islands of different sizes (Wilcove 1985). One means of documenting such differences in nest predation is through controlled experiments using artificial nests. Two recent studies (Loiselle and Hoppes 1983, Wilcove 1985) used artificial wicker nests to examine differences in predation rates for different nest types, habitats, and areas. Both studies used wicker nests with leaves or straw lining the inside of the nest and without modification of the outside of the nest (e.g., Loiselle and Hoppes 1983, Wilcove 1985). Wilcove (1985) noted that these nests were more conspicuous than real nests. Consequently, both he and Loiselle and Hoppes (1983) felt that artificial nests did not measure the actual rate of predation that birds experience, but they assumed that any biases were consistent among sites and nest types. However, this crucial assumption requires testing before further experiments are conducted. In this paper, I report results of experiments that test effects of nest appearance and placement on probability of nest predation.
225 citations
TL;DR: As relative yolk content of eggs increases among 127 species representing 44 families, relative water content decreases and changes are related to a progressive increase in hatchling maturity from altricial to precocial birds according to the classification of Nice (1962).
Abstract: From data in the literature an attempt is made to provide a general overview of the composition of bird eggs and how individual components are related to the relative yolk content, which varies from about 15% in some Sulidae to 69% in the Kiwi (Apteryx). Regression equations are given for the relative water content of the fresh egg, albumen, and yolk, the solid and lipid fractions of egg content, and the calculated caloric density of egg content as a function of relative yolk content. As relative yolk content of eggs increases among 127 species representing 44 families, relative water content decreases. These changes are related to a progressive increase in hatchling maturity from altricial to precocial birds according to the classification of Nice (1962). Certain exceptions to this rule are discussed, namely, eggs of the pelagic feeding Procellariiformes and offshore-feeding terns. Both groups have reduced their clutch to a single egg, have unusually long incubation and fledging periods, and larger relative yolk content than predicted. A general model of egg components is presented which relates the ash, carbohydrate, protein, lipid, water, and caloric content to the relative amount of yolk in the freshly laid egg. Lipids make up 58% of all yolk solids, which have an energy content of 33 kJ-g-'; total solids in egg contents have an average energy content of 29 kJ.g-'. An overview shows how the initial solids and caloric contents are redistributed in the yolk-free neonate and the yolk reserve as well as estimates of the solids and caloric loss during development; energy cost of development is similar in all birds and amounts to ca. 36% of the initial energy content of fresh eggs.
179 citations
TL;DR: It is predicted and confirmed that males within the same dialect have quantitative whistle differences of potential value for individual recognition, and possession of a locally appropriate whistle is a reliable indicator of a male’s age which is a major correlate of male mating success and possibly of male quality.
Abstract: We describe dialects in the flight whistle of the Brown-headed Cowbird and contrast previous hypotheses for the maintenance of dialects with a new one that assumes that a male’s ability to give the correct local dialect is an honest signal of relatively high male quality. The three dialects upon which we focus are part of an extensive dialect system along the eastern Sierra Nevada. The dialects are partially isolated by unsuitable habitat and are unusual because they differ via lexical rather than the less extreme phonetic differences that characterize song dialects in most other species. Because males whistle just before copulating, whistles may function in mate choice. Since flight whistles are also used over long distances, we predicted and confirmed that males within the same dialect have quantitative whistle differences of potential value for individual recognition. Other quantitative analyses indicated phonetic differences among homologous whistle elements from adjacent dialects. Recordings made between 1978 and 1980 showed no quantitative or qualitative differences from a large sample of 142 males recorded between 1983 and 1985. Such temporal stability is expected since the dialects are large, being 10 to 30 km in extent and probably contain hundreds of individuals. Historical records demonstrate that the dialect populations developed since the late 1930s. Males banded in one dialect but recorded in another made up 13.0% of our adult sample and were more likely to have foreign whistles than adults banded and recorded in the same dialect. Yearling males were significantly less likely to whistle than adults, and yearlings that did whistle were significantly more likely to have foreign whistles. Thus possession of a locally appropriate whistle is a reliable indicator of a male’s age which is a major correlate of male mating success and possibly of male quality, as nearly all copulations involve adult males. These age differences are consistent with our new “honest convergence” hypothesis and inconsistent with the local or genetic adaptation hypothesis which predicts that vocal ontogeny is closed by a male’s first breeding season. Bilingual males and those with hybrid whistles combining elements from two dialects made up 0 to 8% of the males within dialect areas. By contrast, 38% of males in one contact zone between two dialects were bilingual and 54% of males in another contact zone gave hybrid whistles. These trends are consistent with the honest convergence hypothesis and inconsistent with hypotheses that dialects are maintained by isolation or because they contribute to local adaptation among populations.
176 citations
TL;DR: It is tentatively concluded that resistance to laying damage has not been critical in favoring the evolution of thick shells in cowbird eggs, and it is shown that a puncture specialist, the Marsh Wren, has greater difficulty puncturingcowbird eggs than the thinner-shelled eggs of various other passerines.
Abstract: We directly measured the eggshell thickness of the three brood parasitic Molothrus cowbirds, 17 other icterids, and 13 additional passerines. By correcting these shell thickness measurements for variation attributable to interspecific differences in egg volume, we show that the Molothrus cowbirds lay eggs with shells that are 30% thicker than expected for their size. Our samples of nonparasitic icterids and of other passerines do not differ significantly in shell thickness values corrected for differences in egg volume. We evaluate two hypotheses for the evolution of unusually thick-shelled eggs in cowbirds. The first, an old idea proposed for parasitic cuckoos, is that thick shells resist damage to the parasite's egg at laying. From indirect tests we could find little or no evidence that the thin-shelled eggs of the hosts of cowbirds were damaged by impact when cowbird eggs were laid in their nests; thus, we tentatively conclude that resistance to laying damage has not been critical in favoring the evolution of thick shells in cowbird eggs. As an alternative hypothesis we propose that thick shells have evolved in cowbird eggs to resist puncture ejections by hosts that are too small to grasp whole cowbird eggs for ejection. We show that a puncture specialist, the Marsh Wren (Cistothorus palustris), has greater difficulty puncturing cowbird eggs than the thinner-shelled eggs of various other passerines. Implications of our hypothesis concerning resistance to puncture ejections are discussed.
138 citations
TL;DR: This report attempts to describe objectively the complete vocal repertoire and the vocal code of the Red Junglefowl (Gallus gallus), most probable wild ancestor of the domestic fowl.
Abstract: This report attempts to describe objectively the complete vocal repertoire and the vocal code of the Red Junglefowl (Gallus gallus), most probable wild ancestor of the domestic fowl. An unconfined color-banded flock was watched over a period of 6 years at the San Diego Zoo. The general behavior and vocalizations are essentially the same in Red Junglefowl and the domestic fowl. Different vocal signals can be recognized by their sonograms and by the common element in the various situations in which a signal is given. Twenty-four vocal signals are described but because of intergradation between some signals and between different situations no absolute size of vocal repertoire can be fixed. A spectrographic (structural) key to the vocal signals of the Red Junglefowl is given and with the sonograms should enable one to identify the typical calls. Different elements can be combined to produce specific vocal signals, in effect a code. Brief, soft repetitive notes of low frequency are attraction calls. Loud harsh sounds with high frequencies are alarm cries. Harsh sounds emphasizing low frequencies are threat sounds. These rules hold for many other birds. Junglefowl also have special calls that appear to indicate well-being, or mild disturbance and frustration. The evolution of the vocal signals of the Red Junglefowl is discussed in relation to Darwin's (1872) three principles of communication and to modern ethology.
134 citations
TL;DR: The rate of food consumption by an adult kittiwake, calculated on the basis of the chemical composition and digestibility of capelin (Mallotus villosus, the most important dietary item at Hopen Island) was 315 g of fresh matter per bird every other day.
Abstract: Rates of CO2 production by breeding Black-legged Kittiwakes (Rissa tridactyla) (mean mass, 386 g) were measured by using doubly-labeled water. Kittiwakes alternated days on and off the nest, while they brooded their nestlings. Field metabolic rates (FMR) in nonforaging birds averaged 2.43 ml CO2/g hr, or 596 kJ/day. This is 1.9 times the basal metabolic rate (BMR), measured in the laboratory to be 1.31 ml CO2/g-hr, or 314 kJ/day. FMRs in foraging birds averaged 4.04 ml CO2/g hr, or 992 kJ/day which is 3.2 times BMR. The rate of food consumption by an adult kittiwake, calculated on the basis of the chemical composition and digestibility of capelin (Mallotus villosus, the most important dietary item at Hopen Island) was 315 g of fresh matter per bird every other day. A colony of 3,000 breeding pairs of kittiwakes at Hopen Island, using the fishing grounds around the island, would consume about 1,245 kg of fresh fish per day, and add about 76 kg (dry matter) of guano to the marine ecosystem during the chick-rearing period.
128 citations
TL;DR: In this article, the authors examined nest-site selection and reproductive success in Piping Plover (Charadrius melodus) over a 4-year period on four nesting beaches in New Jersey.
Abstract: I examined nest-site selection and reproductive success in Piping Plover (Charadrius melodus) over a 4-year period on four nesting beaches in New Jersey. Nest site characteristics varied among the four nesting locations with respect to distance to dunes, water, nearest Least Tern (Sterna antillarum) nest, and percent shell cover. Compared with random points, Piping Plover nests were closer to dunes and vegetation, farther from water, closer to tern nests, farther from other Piping Plover nests, in spots with more shell cover. Reproductive success varied among colonies and years, but was generally higher at Brigantine than the other sites. Causes of nest failure included predation, human destruction, abandonment, and flooding. Plovers derived antipredator benefits from nesting near terns, and plover nesting in tern colonies often had higher success than those nesting outside of tern colonies.
117 citations
TL;DR: In this paper, the authors examined yearly trends in bird abundance in relation to changing vegetation structure and composition and in relation with yearly weather variation and found that changing vegetation structures resulted in predictable trends related to the foraging and nesting habits of the birds.
Abstract: We summarized breeding bird censuses done from 1966 to 1985 on two Sierra Nevada forest plots, one that was burned in 1960 and an adjacent, unburned control. Our objective was to examine yearly trends in bird abundance in relation to changing vegetation structure and composition and in relation to yearly weather variation. From 1969 to 1983 shrub cover on the burned plot increased from about 22% to over 43%, and density of overstory trees increased by about 50%. Herb and grass cover decreased during this period, as did density of snags originally resulting from the fire. During this period of rapid postfire succession, total density of birds was nearly equal on the two plots but species richness increased on the burned plot compared with the unburned plot. Groundand brush-foraging birds were more numerous on the burned plot, and their population size increased significantly from 1966 to 1985. Foliage-searching birds were more numerous on the unburned plot, and their populations were stable over time relative to the burned plot. In contrast, numbers of foliage-searching birds increased significantly on the burned plot. Bark-gleaning birds declined on the burned plot, probably in response to loss of snags used for nesting by most of these species. Variations in weather, as indicated by measures of temperature and precipitation, did not explain yearly variations in bird populations. Rather, changing vegetation structure resulted in predictable trends related to the foraging and nesting habits of the birds we studied.
112 citations
TL;DR: Timing of the decrease in young birds suggests that the onset of reproductive failure occurred in mid-May, well after the nesting season began, and several circumstances of this phenomenon appear to coincide remarkably well with the passage of a radioactive “cloud” from the Chernobyl nuclear power plant accident and associated rainfall.
Abstract: The avian productivity of 51 locally breeding species in coastal grassland, coastal scrub, and mixed evergreen forest habitats was estimated from 11 years of standardized mist-netting data collected between 10 May and 17 August at Point Reyes Bird Observatory’s Palomarin Field Station. A relationship between the number of young birds banded per 100 net hr and the amount of annual (winter) rainfall during the previous season was apparent for the 10 years 1976 to 1985: productivity was low (19 to 32% below the 1 Oyear mean) in years of extremely low rainfall, increased to a maximum (21 to 39% above the IO-year mean) in years of average or slightly above average rainfall, and decreased substantially (20% below the IO-year mean) in years of very heavy rainfall. The number of young birds banded per 100 net hr in 1986, however, was 62.3% below the previous loyear mean and fell well outside the above relationship. This high level of reproductive failure occurred in most of the 51 locally breeding species and was independent of migratory behavior, habitat choice, and nest location. It was not independent of foraging behavior, however, as swallows and woodpeckers, species that feed their young on insects produced in decomposeror detritus-based food chains rather than in primary production-based food chains, showed no significant reduction in productivity. Timing of the decrease in young birds suggests that the onset of reproductive failure occurred in mid-May, well after the nesting season began. Such a large-scale reproductive failure of virtually an entire landbird community has not been reported before and no obvious weather factors appear to explain it. Preliminary data indicate that the reproductive failure was not confined to the vicinity of Palomarin or to central coastal California but rather extended over much of northern California even to the west slope of the Sierra Nevada. It is interesting, but perhaps only coincidental, that several circumstances of this phenomenon, including its timing, appear to coincide remarkably well with the passage of a radioactive “cloud” from the Chernobyl nuclear power plant accident and associated rainfall.
TL;DR: The Mexican Spotted Owl (S. lucida) is even rarer as discussed by the authors, with an estimated 2000 breeding pairs in Washington, Oregon, and California from Kern County northward, with some observers suggest that the owl is so closely tied to old-growth forests in the northern portion of its range that any further harvesting of these forests would reduce the species in proportion to the area harvested.
Abstract: caurina remain in Washington, Oregon, and California from Kern County northward, with an estimated 2000 breeding pairs in that area. The Mexican Spotted Owl (S.o. lucida) is even rarer. Some observers suggest that the owl is so closely tied to old-growth forests in the northern portion of its range that any further harvesting of these forests would reduce the species in proportion to the area harvested. Many millions of dollars of timber and related jobs hinge on the outcome of decisions made on harvesting of old-growth timber. Thus the biology of this owl is a sensitive
TL;DR: Three solo measures (number of feeding visits, prey size, and number of prey) were evaluated as estimators of daily prey volume and effectiveness of any one of these estimators varied between sexes and each of these variables generally explained less than 50% of the variation in daily preyVolume returned by an adult.
Abstract: The influence of parental sex, brood size, and nestling age in determining the rate of feeding of nestling Mountain Chickadees (Parus gambeli) is examined. Male Mountain Chickadees provide a majority of the food delivered to nestlings. For most of the nestling cycle, the male feeds each nestling a greater volume of food than does the female. His relative share of feeding visits increases with increasing brood size. Although the male's feeding contribution is large, the female predominates in other aspects of parental investment. Throughout the nestling cycle, female nest attendance times are at least twice as long, on average, as the male's. Her attendance time increases as brood size declines. Each nestling in a smaller brood receives a greater volume of food and more feeding visits than counterparts in larger nests. Prey volume per nestling, visits per nestling, size of individual prey, and prey volume per trip all exhibit a rising phase over the initial 5 to 10 days of the nestling cycle followed by a level phase till near fledging time. Load size, however, increases almost continuously throughout the cycle. Three solo measures (number of feeding visits, prey size, and number of prey) were evaluated as estimators of daily prey volume. Effectiveness of any one of these estimators varied between sexes and each of these variables generally explained less than 50% of the variation in daily prey volume returned by an adult. Therefore, care should be taken in equating such estimators to more complex measures of feeding effort like prey volume.
TL;DR: In this paper, the authors examined how the nest-defense behavior of American crows has been modified by the presence or absence of persecution and found that in an area of high human density and low persecution, crows should habituate to human beings near their nests and in areas of high persecution, they should show avoidance behavior to human intruders near their nest.
Abstract: The American Crow (Corvus brachyrhynchos) has traditionally been persecuted as a pest and hunted for sport. As recently as 1980 there were an estimated 4,530,000 crow hunter-days in the United States (USDI and USDC 1982a). In recent decades crows, which in the past were typically rural birds, have begun nesting in cities where ordinances prohibit the discharge of firearms. As a result of this colonization of urban areas, two adjacent crow populations exist in many regions, a persecuted rural one and a protected urban one. We took advantage of this situation to examine how the nest-defense behavior of crows has been modified by the presence or absence of persecution. We examined two complementary hypotheses: (1) in an area of high human density and low persecution, crows should habituate to human beings near their nests and (2) in areas of high persecution, crows should show avoidance behavior to human intruders near their nests.
TL;DR: The volume of male eggs in Mountain White-crowned Sparrows was slightly larger than that of female eggs in every year of a 5-year study, consistent with facultative manipulation of offspring sex as proposed under the Trivers and Willard hypothesis.
Abstract: The volume of male eggs in Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) was slightly larger than that of female eggs in every year of a 5-year study. The volume difference was highly significant (P < 0.01) when data for all years were combined. Male nestlings also grew faster than female siblings. Natural history observations on adults suggest that reproductive success is more variable in male than in female Whitecrowned Sparrows. Taken together, these data are consistent with facultative manipulation of offspring sex as proposed under the Trivers and Willard hypothesis (1973). In avian species it may be necessary when testing this hypothesis to consider the relationship between sex and parental investment for individual offspring rather than focusing solely on differences between broods.
TL;DR: The results support the predator-protection advantage of feeding within a flock independent of the feeding-efficiency hypotheses.
Abstract: We studied adult White Ibises (Eudocimus albus) on a South Carolina salt marsh to determine the effects of social grouping on the birds' foraging behavior. White Ibises on our study site fed almost exclusively on fiddler crabs (Uca spp.). Four social categories were recognized: (1) central adults in flocks of 15 birds, (2) peripheral adults in flocks of 15 birds, (3) adults in small flocks of five or fewer birds, and (4) solitary adults (singletons). We used a paired sampling scheme to compare the behavior of ce tral birds with the behavior of birds in the other three social groupings. Although peripheral adults did not differ significantly from central adults in number of steps, number of crabs captured, or number of capture attempts, they looked up more often and for longer periods of time than did central adults. Behavior of solitary ibises was similar to that of ibises in small flocks, but both foraged differently than central adults in large flocks. Birds in the center of large flocks took fewer steps, probed more frequently, and scanned the surroundings less often than birds in the other two social groupings; there were no differences in capture rates. Thus, White Ibises used two distinct types of foraging strategies depending on flock size and their position within the flock. Ibises in small flocks, singletons, and, to some extent, ibises on the edges of large flocks, stepped quickly to capture fiddler crabs before the crabs could retreat into burrows. Centrally-located ibises in large flocks were unable to use this foraging technique because the surrounding members of the flock created a disturbance that caused the fiddler crabs to remain in their burrows. These birds, therefore, probed into crab burrows and found their prey by tactile means. Our results support the predator-protection advantage of feeding within a flock independent of the feeding-efficiency hypotheses.
TL;DR: The difference in nesting success and antipredator behaviors is discussed in terms of greater detectability in golden-plovers than dotterels, and of biparental (golden-plover) versus uniparental(dotterel) care.
Abstract: Breeding success and antipredator behavior of Greater Golden-Plovers (Pluvialis apricaria) and Eurasian Dotterels (Charadrius morinellus) were studied in Norway over seven summers in an area 1,200 to 1,350 m altitude. Behavior was recorded in a standardized manner on nest inspections, on approaching parent birds with chicks, and by observing reactions to overflying predators on scheduled observation bouts. Red foxes (Vulpes v&es), Common Ravens (Corvus corax), and Mew Gulls (Larus canus) were the most important nest and chick predators in the area. Nest predation was calculated from exposure time. During incubation both species either sneaked away from the nest when approached by a human (golden-plovers at a much larger distance than dotterels) or sat tightly and flushed at a short distance giving distraction display. “Sneaking” had a positive effect on nest survival, and ground distraction displays had a better effect on nest survival than flight distraction displays. After hatching, golden-plover parents exposed themselves to an approaching human at several hundred meters distance by loud alarm calls and by encountering the intruder, whereas dotterels kept unobtrusive until approached to about 40 m, and upon further approach finally gave distraction displays on the ground. Avian predators at a longer distance (~300 m) from nest or chicks at most aroused alertness, while at close quarters (~50 m) they induced golden-plovers to squat flat, while dotterels exposed themselves by “tail-flagging.” Nest loss was greater for golden-plovers (78%) than for dotterels (47%), while chick loss was greater for dotterels (65%) than for golden-plovers (28%). The difference in nesting success and antipredator behaviors is discussed in terms of greater detectability in golden-plovers than dotterels, and of biparental (golden-plover) versus uniparental (dotterel) care.
TL;DR: Female Mallards demonstrated a higher condition capacity than males, which may contribute to the more rapid recovery of female primaries, and wing length is probably not a variable suitable for use in a condition index.
Abstract: The effects of high and low protein food on molting in penned, wild-strain Mallards (Anas platyrhynchos) from southwestern Sweden were studied in 1979, 1980, and 1985. Body condition, as indicated primarily by lipid deposits, declined during the flightless period. This decline was probably more the result of a strategy to recover flight capability rapidly than the result of stress. By metabolizing stored lipids, birds may be able to seek refuge in habitats offering protection from predators, even if food in such habitats is scarce. During the flightless period, food quality did not affect the growth rate of the primary feathers. But when exposed to low protein food, even after recovering flight capability, birds, especially males, developed shorter wing feathers; this feather shortening may reduce their condition capacity, i.e., their capacity to increase body condition without reducing their flight capacity in late autumn. A lowered condition capacity could lead to decreased survival of the ducks when exposed to severe winter conditions. Female Mallards demonstrated a higher condition capacity than males, which may contribute to the more rapid recovery of female primaries. Since the final length of the primaries is affected by food quality during molting, wing length is probably not a variable suitable for use in a condition index.
TL;DR: Insectivorous bird flocks were observed in all types of forested habitats during the non-breeding season in western Mexico as discussed by the authors, and the species composition of flocks changed markedly and predictably among five categories of habitat type.
Abstract: Insectivorous bird flocks were observed in all types of forested habitats during the nonbreeding season in western Mexico. The species composition of flocks changed markedly and predictably among five categories of habitat type. The average number of species per flock in lowland habitats was 4.7, while a mean of 18.6 species participated in highland flocks, ranking the latter among the most species-rich flocks in the world. The mean proportion of the local insectivorous pecies that participated in mixed-species flocks was significantly greater in the highlands (6 1.3%) than in the lowlands (24.6%). About half of the flock participants in both undisturbed lowland and highland habitats were north temperate migrants, ranking west Mexican flocks among the most migrant-rich in the world as well. In highland flocks, the maximum number of individuals per attendant species was generally two to three, but there were often six to twelve individuals belonging to each of several nuclear species. The lowland deciduous forest flocks seemed to lack nuclear species.
TL;DR: Handle methods and efficiencies of 26 species of Paraguayan birds feeding on fruits of Allophyllus edulis indicate that these species need to spend relatively little time feeding to meet their estimated energetic needs, and that handling time has a relatively trivial effect on the time/energy budgets of the bird species observed.
Abstract: I report on handling methods and efficiencies of 26 species of Paraguayan birds feeding on fruits of Allophyllus edulis (Sapindaceae). A bird may swallow fruits whole (Type I: pluck and swallow feeders), hold a fruit and cut the pulp from the seed with the edge of the bill, swallowing the pulp but not the seed (Type II: cut or mash feeders), or take bites of pulp from a fruit that hangs from the tree or that is held and manipulated against a branch (Type III: push and bite feeders). In terms of absolute amount of pulp obtained from a fruit, and amount obtained per unit time, Type I species are far more efficient than Type II and III species. Bill morphology influences feeding methods but is not the only important factor. Diet breadth does not appear to be significant. Consideration of feeding efficiency relative to the needs of the birds indicates that these species need to spend relatively little time feeding to meet their estimated energetic needs, and that handling time has a relatively trivial effect on the time/energy budgets of the bird species observed.
TL;DR: Between July 1983 and September 1984, the cormorant population recovered whereas the penguin population had not recovered; the Greater Flamingo population size remained unchanged.
Abstract: The 1982-83 El Nifio/Southern Oscillation was the most severe recorded in the tropical Pacific Ocean. It was a period of low ocean productivity. Many seabirds in the Galapagos Islands, including the Galapagos Penguin (Spheniscus mendiculus) and the Flightless Cormorant (Nannopterum harrisi), did not breed. The cormorant and penguin populations were reduced by 49 and 77%, respectively. The Greater Flamingo (Phoenicopterus ruber) population size remained unchanged. Between July 1983 and September 1984, the cormorant population recovered whereas the penguin population had not recovered.
TL;DR: For example, the relative dominance and relative density of oak (Quercus spp.) was significantly less at nest sites whereas that of eastern hemlock (Tsuga canadensis) was significantly greater as discussed by the authors.
Abstract: Vegetational and topographical factors of22 nest sites of the Northern Goshawk (Accipiter gentilis) were compared to random forest plots. Goshawks selected sites with greater basal area, fewer saplings, and significantly greater numbers of trees 20 to 40 cm in diameter. The relative dominance and relative density of oak (Quercus spp.) was significantly less at nest sites whereas that of eastern hemlock (Tsuga canadensis) was significantly greater. Goshawks did not use southern slopes for nesting and nests were often found at higher elevations than random sites. Nest sites were significantly further from human habitation, but were significantly closer to swamps and woods roads (or discernable trails) than random sites. Despite the significant preference for conifers in the nest sites, deciduous hardwoods were more often used as nest trees (82%) with American beech (Fagus grandifolia) and black birch (Betula lenta) being used more than expected.
TL;DR: The lack of a relationship between the number of chases involving females and dive displays with variations in food quality, along with observations of long territory tenure, suggest the primary function of the territory is reproductive and that an internal food source is not necessary for its maintenance.
Abstract: Thirteen territorial male Anna’s Hummingbirds, Calypte anna, were observed during the 1981 and 1982 breeding seasons. Breeding territories were large, but size was not determined by energy availability. When a food source (sucrose solution in feeders) was present, the degree to which it was defended was a function of food quality. If a high-quality food source was absent, males did not exhibit the behaviors associated with defending a food source, but breeding territoriality remained intact. Territories were maintained for the entire breeding season even when food quality was varied. The lack of a relationship between the number of chases involving females and dive displays with variations in food quality, along with observations of long territory tenure, suggest hat the primary function of the territory is reproductive and that an internal food source is not necessary for its maintenance.
TL;DR: Relative abundances of arthropods on dead and live leaves were similar to those found in the winter period at the same sites, which suggests a period of transition which is consistent with the trial and error learning hypothesis for the development of seasonal foraging specializations in this species.
Abstract: The foraging behavior of Worm-eating Warblers (Helmitheros vermivorus) was studied in Maryland during the breeding season and in Jamaica, Dominican Republic, and Belize during the nonbreeding season. Over 75% of the foraging maneuvers recorded from May to early August in Maryland were directed towards live foliage, whereas over 75% of the maneuvers were directed towards dead curled leaves in the understory of tropical forest in the temperate zone winter. Sampling of the relative abundance of arthropods associated with dead and live foliage showed that although the ratio of total numbers in dead and live leaves was similar in the temperate and tropical sites, the overall ratio of estimated biomass was considerably greater in the tropical sites. This is because large arthropods commonly use dead curled leaves as daytime roosts in tropical forests. However, the largest temperatezone arthropods are generally found on leaf surfaces during the day. The winter-foraging specialization on dead leaf arthropods apparently is the more demanding; the most specialized search and attack behaviors are associated with feeding at dead and live curled leaves. I revisited the Belize study sites in September, when Worm-eating Warblers were presumably arriving and found an intermediate use of dead and live leaves. Relative abundances of arthropods on dead and live leaves were similar to those found in the winter period at the same sites. This suggests a period of transition which is consistent with the trial and error learning hypothesis for the development of seasonal foraging specializations in this species.
TL;DR: Black Guillemots can maintain higher reproductive rates than offshore-feeding Alcidae because their short foraging range and the temporal and spatial predictability of their benthic prey permit higher rates of chick provisioning.
Abstract: I studied chick growth and parental provisioning behavior of Black Guillemots (Cepphus grylle) in Hudson Bay, Canada. Chicks received benthic blennies, principally Stichaeus punctatus and Eumesogrammus praecisus, which parents caught in water less than 40 m deep close to the colony. Chick feeds were more frequent in the morning but feeding rates did not vary with age of young. Size of prey items increased during the nestling period, and energy intake peaked at about 780 kJ/day/chick when chicks were 25 days of age. Black Guillemots can maintain higher reproductive rates than offshore-feeding Alcidae because their short foraging range and the temporal and spatial predictability of their benthic prey permit higher rates of chick provisioning.