bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Role of Plumage Polymorphism in Dominance Relationships of the White-throated Sparrow
Authors: Watt Doris J. , Ralph C. John , Atkinson Carter T. 
Published: October 2019

Abstract
We studied dominance behaviors of captive winter flocks of White-throated Sparrows (Zonotrichia albicollis) in central Pennsylvania. Preliminary tests with a small group of birds indicated that there might be differences in behaviors between color morphs if age and sexual differences were controlled. Studies of two larger groups produced considerable variation in results between the groups. One group displayed striking correlations between dominance ability and color. In this group white adult males dominated others more than tan adult males did, whereas tan immature males, adult females, and immature females were more often dominant than were white immature and female birds. The second group did not display such striking differences. Tan adult and immature females were more dominant than white females, as in the first group, but not significantly. Immature males displayed the opposite trend from the first group-white morphs were more dominant than tans. Adult males in the second group showed no clear trend. We also found differences in dominance between tan and white females that appeared to depend on season, white birds dominating tan birds in a small group in the spring, a reversal of relationships documented in the fall. Within age-sex classes, dominant females in both large groups tended to be duller in plumage brightness (scaled as an index) than were subordinate females. In one of the two large groups, duller immature males were more dominant than brighter ones, while brighter adult males tended to be more dominant than duller ones. We suggest that the relationships between immature male plumage and dominance may be influenced by the morph of adult males of specific dominance status in the flock. Spring plumage indices were more often correlated with fall dominance differences than were fall plumage conditions, suggesting a genetic or causal relationship between dominance and plumage rather than a proximate (status signaling) function. Recorded morph frequencies from this study and the literature support the hypothesis that selection is balanced between the two morphs and is dependent on the advantages or disadvantages of aggressiveness within a sex.
Feeding Schedule and Daily Food Consumption in Red-Throated Loons (Gavia stellata) over the Prefledging Period
Authors: Reimchen T. E. , Douglas Sheila 
Published: October 2019

Abstract
We describe parental feeding activities of Red-throated Loons (Gavia stellata) throughout the prefledging period at two freshwater nesting territories in coastal British Columbia. The nesting lake contained resident fish populations, but adult loons fed marine fish to their young, making an average of 11 flights per day (average duration 60 min per flight) to the ocean and returning each time with a single fish. Small shallow-bodied fish (Ammodytidae, Pholidae), which were easily swallowed by chicks, predominated in the diet during the 3 days following hatching. The total weight of fish fed to the chicks per day (8-194 g) increased over the prefledging period: adults returned fewer but larger fish (Embiotocidae) as the chick aged. Of the fish offered, 4% were too large for the chick to swallow.
The Effect of Temperature and Clutch Size on the Energetic Cost of Incubation in a Free-Living Blue Tit (Parus caeruleus)
Authors: Haftorn Svein , Reinertsen Randi Eidsmo 
Published: October 2019

Abstract
The energetic cost of incubation of a free-living Blue Tit (Parus caeruleus) female was studied during two breeding seasons by measuring the rate of oxygen consumption in a nest box converted into a metabolic chamber. Like its congeners, only the female Blue Tit incubates and during that time is fed by the male. Just before and during the egg-laying period the female spends the night in the nest. Because of the progressive development of incubation behavior during this period, it is possible to measure the oxygen-consumption rate of a nonincubating female (resting metabolism) and to compare it with values obtained later when the bird is incubating a full clutch under otherwise similar conditions. The air temperature in the metabolic chamber was regulated experimentally. The results show that the energy cost of incubation is relatively important below the lower critical temperature (about 15°C). With a fall in the air temperature, energy expenditure increased in relation to that of the resting metabolism. The energy cost of incubation also increased with clutch size, by about 6-7% for each additional egg. At air temperatures around 0°C, which are frequent under natural conditions in Fennoscandia, the female must increase her metabolic rate by 50-90% to keep the eggs in a normal-size clutch (10-13 eggs) warm. During the last days of incubation we accounted for the metabolism of the embryos, which on the day before hatching contributed about 15% of the total oxygen consumption when the female was incubating a clutch of 13 eggs.
Comparative Reproductive Success of Yellow-Shafted, Red-Shafted, and Hybrid Flickers across a Hybrid Zone
Authors: Moore William S. , Koenig Walter D. 
Published: October 2019

Abstract
Alternative hypotheses of hybrid zones make specific predictions about reproductive components of fitness in the hybrids. The dynamic-equilibrium and reinforcement hypotheses are premised on reduced hybrid fitness, which should be apparent as reduced clutch or brood size or as increased embryonic mortality. The hybrid-superiority and introgression hypotheses predict normal clutch and brood size and embryonic mortality.
Reproductive success was measured at four study sites on a transect across the hybrid zone between the Yellow- (Colaptes auratus auratus) and Red-shafted (C. a. cafer) subspecies of the Northern Flicker. Two additional clutch size samples representing pure Yellow- and Red-shafted flickers were obtained from museum egg collections. Mean clutch size did not differ significantly among the six samples. Factorial ANOVAs showed that early clutches and broods are larger than late clutches and broods, but no significant difference was detected between hybrid and parental study sites. Analyses of the effect of phenotype (yellow-shafted, red-shafted, hybrid) also suggest that neither clutch size nor brood size is affected, with the exception that hybrid males sired significantly smaller broods. Finally, there were no significant effects of type of cross (red-shafted male × hybrid female, etc.) on the ratio brood-size/clutch-size.
The only evidence for reduced hybrid fitness was in the test where males with hybrid phenotypes appear to have sired small broods. This may indicate that abnormal behavior of hybrid males affects female fecundity, but it is also plausible that this marginally significant result is a type I statistical error. The overall lack of evidence for reduced hybrid fitness is inconsistent with either the dynamic-equilibrium or reinforcement models. Of the two remaining alternatives, the bounded hybrid-superiority model appears the more likely explanation of the Northern Flicker hybrid zone because earlier work (Moore and Buchanan 1985) showed that the hybrid zone is not becoming broader, as predicted by the introgression model.
Reversed Sexual Size Dimorphism: Effect on Resource Defense and Foraging Behaviors of Nonbreeding Northern Harriers
Authors: Temeles Ethan J. 
Published: October 2019

Abstract
Sexual differences in resource defense and foraging behaviors during the nonbreeding season are detailed for Northern Harriers (Circus cyaneus) in California. Female harriers hunted more frequently in high (>0.5 m) vegetation than males. In addition, females hunted at slower speeds and used different hunting behaviors than males. Females in high vegetation showed a significantly greater response (i.e. attack) rate to approaching harriers than males, and females won nearly all (28/29) aggressive interactions with males. These results suggest that sexual differences in harrier foraging behavior during the nonbreeding season result from females excluding males from preferred foraging areas and males adopting alternative foraging strategies. Foraging strategies of harrier sexes are compared with foraging strategies of sexes of birds in which males are larger than females to examine the role of body size in determining sexual foraging strategies.
Density Trends and Range Boundary Constraints of Forest Birds Along a Latitudinal Gradient
Authors: Emlen John T. , DeJong Michael J. , Jaeger Michael John , Moermond Timothy C. , Rusterholz Kurt A. , White Robin P. 
Published: October 2019

Abstract
We plotted the density distributions of 41 land-bird species along a 1,200-km transect spanning 7°28′ (865 km) of latitude through relatively uniform bottomland deciduous forest in middle North America. Standardized counts and observations at 12 survey stations, closely matched in habitat structure and widely distributed along the route, provided population data for all species and indices of total avian foraging pressure (consuming biomass) on each of six major foraging substrates.
Density curves for species fluctuated considerably from station to station but tended to be level across range centers and slope peripherally to north and south boundaries at rates of 3-30% per degree of latitude. Substrate foraging pressures declined northward on the aerial and midfoliage substrates and southward on the low-foliage substrate. Summed community densities showed no significant latitudinal trends.
We used the distinctive distribution patterns of climate (smooth latitudinal gradients), habitat structure (irregular mosaics of vegetation patches), and competition (reciprocally sloping density gradients) to identify and evaluate the role of these three constraints along the transect. Progressive latitudinal trends in species abundance thus were attributed to climatic factors, irregular station-to-station fluctuations to habitat factors, and inversely sloping density trends in paired profiles to competition. On this basis all species apparently responded to both climatic and habitat factors, and about half of the species showed suggestions of competition. In a correlation analysis across the 12 stations, latitude per se most closely matched density distribution in 12 species, one or another of the habitat parameters in 25 species. We proposed that season length (days available for breeding activity) was the principal constraining attribute of latitude at northern range boundaries, day length (hours available for feeding and provisioning young) at southern boundaries.
Boundaries have been essentially stable during the past 50-100 yr in most species, but the northern boundary expanded northward in one species following human-induced habitat enhancement, and temporarily receded southward in another following a winter of severe stress. We attribute this general stability of range boundaries over time to within-population gene flow and the associated peripherally declining mean fitness of phenotypes adapted to central range conditions along radially diverging environmental gradients.
We suggest that two boundary lines should be recognized for each species, an inner functional boundary at the line where birth rates drop below death rates, and an outer empirical boundary at the limit of recorded occurrences.
Differences in Sexual Size Dimorphism and Body Proportions between Adult and Subadult House Sparrows in North America
Authors: McGillivray W. Bruce , Johnston Richard F. 
Published: October 2019

Abstract
North American samples of House Sparrows (Passer domesticus) collected by R. F. Johnston and R. K. Selander (see Johnston and Selander 1971, Johnston 1973) were separated into adult (19 localities) and subadult (21 localities) groups. Significant clines were generated for all age and sex combinations through regression of locality means for body size against environmental seasonality. The strong body-size clines for subadult House Sparrows suggest a large genetic component to geographic variation in House Sparrow body size. There were no significant differences between the male and female clines for either age group. Therefore, there was no consistent relationship between sexual size dimorphism (SSD) in adult House Sparrow populations and environmental factors. Adult levels of SSD were higher than subadult levels at localities with distinct seasonalities. This resulted from selection against relatively large subadult females in areas with cold winters. Adult males were larger than subadult males, but whether this represented growth or selection is equivocal. The ratio of body core to limb variables was correlated poorly with the winter temperatures of the collecting localities.
The relationship improved if samples from coastal areas were excluded. Adult levels of this ratio were higher than subadult levels at localities with low January temperatures. Overwinter changes in both House Sparrow size and shape can be correlated with environmental variables. Although selection for efficient thermoregulatory design is implied, it is difficult to account for the mortality of large subadult females over cold winters and to completely discount the effects of growth.
Habitat Use by Wading Birds in a Subtropical Estuary: Implications of Hydrography
Authors: Powell George V. N. 
Published: October 2019

Abstract
The dynamics of foraging habitat use by long-legged wading birds was analyzed with respect to water-level fluctuation patterns in Florida Bay. Wading-bird presence at four sites situated to sample the heterogeneity of the bay was quantified by repeated surveys collected throughout the day and year. Models for habitat availability were generated using water-level data collected from continuous recorders, staff guages, and habitat profile maps. These models were tested against the survey data.
Roseate Spoonbills (Ajaia ajaja) foraged on the study areas primarily at night. Great Blue Herons (Ardea herodias) fed both day and night, but primarily at night where the tidal range was small. Great Egrets (Casmerodius albus), Snowy (Egretta thula) and Reddish (E. rufescens) egrets, Little Blue (E. caerulea) and Tricolored (E. tricolor) herons, and White Ibis (Eudocimus albus) fed during daylight. Where tidal range was small (<5 cm) diurnal species fed throughout the day.
Florida Bay has a pronounced annual water-level cycle that causes monthly mean water levels to vary by as much as 30 cm between October (high) and May (low). Models derived from hydrology data predicted that this seasonal variation in water level would have a major impact on habitat availability, particularly where tidal flux was small. The predictions were supported by survey data. At sites with minor tides, most wading-bird species had a cycle in seasonal abundance that correlated with seasonal changes in water level; only the tallest species, Ardea herodias, was uniformly present throughout the year. The large daily range in tide (x̄ = 80 cm) afforded year-round access to foraging habitat, and these abundance patterns did not exist. The seasonal variability in habitat availability has major management implications because the maintenance of stable wading-bird populations depends on the availability of alternative foraging sites when water levels are high. Historically, these sites have tended to be targeted for human development.
Effects of Food Supplementation, Song Playback, and Temperature on Vocal Territorial Behavior of Carolina Wrens
Authors: Strain Joy G. , Mumme Ronald L. 
Published: October 2019

Abstract
We found both the song rate and the rate of song-type change of male Carolina Wrens (Thryothorus ludovicianus) in winter were positively correlated with ambient temperature. When the effect of temperature was controlled statistically, food supplementation significantly increased both the song rate and the rate of song-type change. Song playback did not significantly increase either song rate or rate of song-type change, however. Because foraging and singing are mutually exclusive behaviors in Carolina Wrens, the increase in vocal territorial behavior associated with warmer temperatures and food supplementation may reflect a decrease in the time required for foraging. The rate of vocal territorial behavior in winter may be more dependent on the amount of food available to wrens than on the presence of intruders.
Evidence Against Observational Learning in Storage and Recovery of Seeds by Black-Capped Chickadees
Authors: Baker Myron Charles , Stone Eric , Baker Ann Eileen Miller , Shelden Robert J. , Skillicorn Patricia , Mantych Mark D. 
Published: October 2019

Abstract
Recovery of cached sunflower seeds by Black-capped Chickadees (Parus atricapillus) was observed in four laboratory experiments. Results of the first experiment were consistent with the hypothesis that chickadees use spatial memory to recover seeds cached 24 h earlier. The second experiment demonstrated that individuals have a high recovery rate for their own caches and a low recovery rate for caches made by another. The third and fourth experiments demonstrated that one chickadee observing another caching seeds provided no recovery benefit to the observer in comparison to its performance when recovering seeds hidden in its absence. This result held for 2-h and for 6-min delays between observation and attempted recovery. We believe that spatial memory is used by chickadees, that the individual carrying out the caching has a large recovery advantage over a conspecific that searches the same patch, and that the perceptual and motor experience involved in the act of traveling to a cache location may be necessary for the establishment of spatial memory.
Red Color Bands Reduce Fledging Success in Red-Cockaded Woodpeckers
Authors: Hagan John M. , Reed J. Michael 
Published: October 2019

Abstract
An analysis of the effects of colored leg bands on Red-cockaded Woodpeckers, in a long-term field study, showed that males that wore red bands fledged significantly fewer young than males without red bands. Other colors were unrelated to fledging success. Band color had no detectable effect on the fledging success of adult females. The offspring sex ratio of breeding males wearing red bands was significantly female-biased. Offspring sex ratios were not related to the presence or absence of red bands on breeding females. Wearing a red band did not affect the probability of a male attracting a mate or the probability of switching mates. For both sexes, annual age-specific survival was independent of the presence or absence of a red band, but nestlings wearing red bands were less likely to be sighted as fledglings. Males with red bands fledged fewer young, consistent with both the species-recognition hypothesis and the coverable-badge hypothesis. The coverable-badge hypothesis, which predicts that the inability to conceal a voluntary social signal (the red cockade) can be detrimental, is the more parsimonious explanation of our results.
Adjustment of Parental Investment with Mate Quality by Male Yellow-Headed Blackbirds (Xanthocephalus xanthocephalus)
Authors: Gori David F. 
Published: October 2019

Abstract
By removing young from the nests of competent females, I tested whether male Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) could assess the parental competence of mates and adjust their parental investment accordingly. The purpose of this experimental reduction was to equalize the number of young in nests of parentally competent and incompetent females in order to control for the effect of offspring number on parental investment by males. Males had a greater probability of feeding at nests of competent-reduced females and they fed at a higher rate than they did at nests of incompetent females. The latter broods were fed only when nests belonging to competent females were unavailable. Males adjust their parental investment with mate quality independent of the number of young in nests. To explain this preference, I constructed functions to relate the amount of paternal investment (i.e. male feeding rate) to the number of young fledged from nests and the fledging mass of young. The latter are two components of male reproductive success and, therefore, estimates of the "return" on a male's parental investment. Male feeding had no effect on the number of young fledged from starvation-reduced or experimental nests. However, the fledging mass of young increased more when males helped competent females than when incompetent females were helped. Thus male preference for helping competent females may result because the return per unit of their investment is greater at these nests.
Early Growth and Development of the Common Barn-Owl's Facial Ruff
Authors: Haresign Tim , Moiseff Andrew 
Published: October 2019

Abstract
The ability of the Common Barn-Owl (Tyto alba) to localize sounds produced by potential prey can be explained on the basis of sensitivity to differences in interaural time and intensity. The size of the owl's head is a prime determinant of interaural time differences, whereas the facial ruff is the prime determinant of interaural intensity differences. During the 60 days following hatching, the physical structures that establish these binaural cues undergo massive growth. Barn-owl chicks are altricial and scantily feathered when they hatch. Growth of the head and ruff feathers occur at separate times during early maturation. Between 11 and 30 days after hatching, the diameter of the head approximately doubles. Between 35 and 60 days, facial ruff feathers emerge and grow to nearly adult length (ca. 20 mm). During the first 60 days of life, the barn-owl auditory system would be subject to widely varying binaural cues which eventually stabilize.
The Costs and Benefits of Egg Destruction by Conspecifics in Colonial Cliff Swallows
Authors: Brown Charles R. , Brown Mary Bomberger 
Published: October 2019

Abstract
We studied egg destruction by conspecifics in colonial Cliff Swallows (Hirundo pyrrhonota) in southwestern Nebraska. Between 8.5% and 19.6% of all nests lost at least 1 egg to an intruding conspecific. Egg destruction occurred when nests were left momentarily unattended, often during colony alarm responses. Birds that destroyed eggs maintained nests of their own, and usually nested within 75 cm of their victims. Egg destruction was not related to attempts to usurp nests. Over a third of perpetrators of egg destruction lost eggs from their own nests to conspecifics. Egg destruction occurred more often in nests initiated early in the nesting season and in nests with large clutch sizes. Egg destruction usually occurred during a victim's egg-laying or early during incubation and declined in frequency as incubation proceeded. Breeding in a colony's peak period of nesting did not afford an advantage to potential victims by diluting their chances of being victimized. Cliff Swallows seldom destroyed all of the eggs in a neighbor's clutch, usually destroying only 1 egg at a time even though other eggs were present.
There was little direct evidence that egg destruction was associated with parasitic egg-laying by Cliff Swallows, but nests with egg destruction were over 3 times more likely than nests in general to have an egg physically transferred into them. The costs of egg destruction to victims were obvious, but the benefits to destroyers of eggs were not. Egg destruction is possibly a prelude to physical transfer of eggs, reducing host clutch sizes and ultimately within-brood competition among host and parasitic nestlings. Males may also benefit by destroying a female's eggs during laying, thereby causing her to continue laying and remain sexually receptive to forced extrapair copulations. Incidence of egg destruction by conspecifics increased with Cliff Swallow colony size and thus, for potential victims, represents a definite cost of coloniality.