Seasonal acclimatization to extreme climatic conditions by black-capped chickadees (Poecile atricapilla) in interior Alaska (64 degrees N).

Winters in interior Alaska (64 degrees N) are characterized by short photoperiod (5L : 19D) and chronic subfreezing temperatures. To determine if seasonal acclimatization of black-capped chickadees (Poecile atricapilla) at high latitude differs from that of conspecifics at lower latitudes, standard metabolic rates (SMR), metabolic response to low temperature (-30 degrees C), nocturnal hypothermia, body mass, fat reserves, and conductance were measured over two winters and one summer in three groups of seasonally acclimatized birds. Body mass and conductance did not vary with season, although furcular fat levels were higher in winter. Birds used nocturnal hypothermia when exposed to -30 degrees C in summer or winter. Although SMR did not vary seasonally, winter SMRs differed between the two winters of the study. Nocturnal hypothermia in summer and decreased SMR in response to extreme conditions may either reflect plasticity inherent to all populations of black-capped chickadees or may result from individual variation within this northern population.     

Food hoarding behaviour of black-capped chickadees (Poecile atricapillus ) in relation to forest edges

In temperate forests, small birds avoid the use of forest edges in adverse winter weather suggesting high foraging costs in terms of energetic requirements. Since hoarding species will often retrieve caches during adverse winter weather, they may perceive forest edges, especially exposed ones, as low quality hoarding sites. We tested whether black-capped chickadees ( Poecile atricapillus) inhabiting fragmented forests modify and reduce hoarding activity near forest edges. We also tested whether hoarding behaviour will be most affected in sites with forest edges more exposed to extreme weather. Black-capped chickadees taking food from a feeder 30 m from the nearest forest edges hoarded items mostly towards the forest interior, whereas no preference in hoarding location was observed with birds taking food from a feeder placed >100 m from the edge. Furthermore, birds avoided direct flights towards forest edges and, at sites exposed to prevailing winds, hoarding trips were shorter than at other locations. These results suggest that individuals avoid hoarding near forest edges and there, they lower their investment in terms of hoarding effort. The observed difference in hoarding behaviour was more evident near forest edges delimiting wide unforested areas than in edges delimiting narrower unforested areas. Edge exposure to prevailing winds influenced hoarding behaviour much less. We suggest that hoarding birds may partially overcome the ecological costs of habitat loss and fragmentation due to abiotic edge effects. By hoarding food away from forest edges in good weather, they may use forest interiors as low-cost retrieval sites under adverse weather.     

Parental aggression in black-capped chickadees

Black-capped chickadee (Parus atricapillus) adults are aggressivetoward their young after the young have fledged. We examinetwo hypotheses to explain the function of this aggression. Eightfamilies were observed throughout the period after fledgingto see if aggressionfunctions in discouraging the youngs' dependenceon their parents for feedings or in encouraging dispersal ofyoung from the natal territory. Aggression consisted mostlyof chases, supplantings, and attacks. Most aggressive interactionsoccurred when young were following a parent closely or begging.After an aggressive act, fledglings tended to move away fromthe parent and forage on their own. The frequency of aggressiveacts peaked at 13 days after fledging, then decreased. Thispeak occurred when fledglings were making the transition fromdependence on parental feedings to independent foraging. Mostfledglings had not dispersed by 22 days after fledging. Ourresults support the hypothesis that parental aggression encouragesfledglings to forage independently, rather than to dispersefrom the natal territory.     

Evidence of accelerated beak growth associated with avian keratin disorder in black-capped chickadees (Poecile atricapillus)

We recently documented an epizootic of beak deformities in more than 2,000 Blackcapped Chickadees (Poecile atricapillus) and other wild bird species in North America. This emerging avian disease, which has been termed avian keratin disorder, results in gross overgrowth of the rhamphotheca, the outer, keratinized layer of the beak. To test the hypothesis that the beak deformities characteristic of this disorder are associated with accelerated keratin production, we measured rates of beak growth and wear in affected Black-capped Chickadees (n=16) and a control sample of unaffected chickadees (n=14) collected from south-central (61°09'-61°38'N, 149°11' -149°48'W) and interior Alaska (64°51' -64°53'N, 147°49' -147°59'W). Rates of absolute growth were 50-100% higher in affected birds than they were in control birds and exceeded records from other passerine species. These results suggest that abnormally rapid epidermal growth is the primary physical mechanism by which beak deformities develop and are maintained in affected chickadees. Although beak overgrowth typically worsened over time, differential patterns of wear influenced the severity and morphology of deformities. In some cases, the effects of accelerated keratin growth were partially mitigated by frequent breakage of rhamphothecal tips. However, mortalities occurred in 9 of 16 birds (56%) with beak deformities during the study, suggesting that avian keratin disorder results in severe health consequences for affected birds. Additional study of factors that control beak keratin production is needed to understand the pathogenesis of this debilitating disease in wild birds.     

Achromatic plumage reflectance predicts reproductive success in male black-capped chickadees

The size of achromatic (black, white, gray) plumage patchesserves as a male status signal in many species of birds, butvariation in the colors of these patches has received littleattention. We assessed the relation between achromatic plumagereflectance, dominance rank, body condition, and reproductivesuccess in male black-capped chickadees, Poecile atricapillus.We measured plumage reflectance for five body regions of 40male chickadees in late winter and monitored these males throughoutthe following breeding season to determine whether they survivedto breed, whether they successfully paired, whether their partnerlaid eggs, and both their apparent and realized reproductivesuccess. As expected from past studies, a male's dominance ranksignificantly predicted whether his partner laid eggs. However,only achromatic plumage reflectance significantly predictedother measures of male reproductive performance. Among maleswho fledged at least one offspring, both the brightness of whiteplumage regions and the UV-chroma of melanin-based plumage regionswere significant predictors of the proportion of within-pairyoung in their nests. When we consider all males we measured,assigning zero values to males who failed to sire any offspring,the UV-chroma of melanin-based plumage regions was a significantpredictor of realized reproductive success. Bib size was alsorelated to male realized reproductive success. Our findingssuggest that individual variation in achromatic plumage mayplay an important role in sexual signaling in chickadees.     

Overlapping and matching in the song contests of black-capped chickadees

During vocal contests, animals alter both the timing and the patterning of responses to their opponents. Time-specific responses (such as overlapping an opponent's song) and pattern-specific responses (such as matching the type of an opponent's song) may reveal information about interacting animals. Here we explore the consequences of overlapping and frequency matching during song contests of male black-capped chickadees, Poecile atricapillus. Using interactive playback, we engaged birds of high and low dominance status in vocal interactions with a simulated territorial intruder. The playback intruder either overlapped or avoided overlapping the subjects' songs and either matched or avoided matching the frequency of the subjects' songs. Individuals who were overlapped by the playback intruder showed higher variability in their song length and song timing than individuals who were not overlapped. Individuals who were frequency-matched by the playback intruder responded with more agitated responses (more flights and passes over the speaker and closer distances of closest approach) and spent more time farther away from the loudspeaker. We argue that the timing of song delivery and the choice of song type are distinct functional components of vocal interactions, where overlapping and matching songs are threatening signals that have separate consequences for opponent behaviour and song performance. High-ranking males responded at greater distances from the loudspeaker in all treatments and responded with lower agitation levels than low-ranking males. We demonstrate that males of different quality show different behavioural responses to territorial intruders, where males of high status appear reluctant to engage an intruder as intensely as males of low status.     

Pitch-related cues in the songs of sympatric mountain and black-capped chickadees

Acoustic frequency (pitch) cues are known to be important in the recognition of conspecific song in a number of songbird species. Mountain chickadees (Poecile gambeli) and black-capped chickadees (Poecile atricapillus) are sympatric over parts of their ranges and their species-typical songs share many features. I examined the acoustic characteristics of song of these two congeners in a region of sympatry in southern Alberta, Canada. As reported for other populations in allopatry, black-capped chickadees emphasized relative frequency cues in song production. In particular, variation in the ratios between note frequencies was significantly less than variation in the note frequencies themselves. In contrast, songs of mountain chickadees did not have constant frequency ratios and contained an introductory acoustic element absent in black-capped chickadee song. Both species may rely on song note frequency or the presence of this introductory acoustic element when differentiating between conspecific song and heterospecific song. Song measures for chickadees in sympatry were similar to measures in allopatry, providing little evidence for character displacement in song production.     

The effects of cache loss on choice of cache sites in black-capped chickadees

Food-storing birds lose a great deal of their stored food toother animals. We examined whether blackcapped chickadees (Parusairicapillus) modify their choice of cache sites using informationthat predicts cache loss. In experiment 1, birds learned toavoid caching at spatial locations where cache loss had previouslyoccurred, but they did not avoid caching near local color cuesthat predicted cache loss. Birds did not modify their generaluse of space in the aviary. Birds also learned to reduce searchingfor caches where spatial location predicted cache loss. Experiment2 confirmed the birds’ ability to discriminate among thespatial locations and the local color cues used in experiment1. In experiment 3, learning a food-rewarded approach to potentialcache sites occurred without any change in the choice of sitesfor caching. We discuss how chickadees selectively associatethe choice of cache site with its consequences, even over delaysof several hours between caching and cache recovery.     

Honest advertisement and song output during the dawn chorus of black-capped chickadees

Costly signals can evolve under sexual selection, as only thosesignals that are difficult to produce and reflect the relativequality of individuals should be important in mate choice. Onesuch signal may be dawn singing behavior in birds. We assessedwhether the song output at dawn of breeding male black-cappedchickadees Parus atricapilhis honestly reflects quality, whererelative quality is assessed by relative dominance rank in winterflocks. Dawn choruses were recorded from 20 male chickadeesfrom 10 flocks during the fertile period of their mates in 1992,1994, and 1995. Dominance ranks of males were assessed by tabulatinginteractions at winter feeders from 1993 to 1995. A comparisonof the dawn singing behavior of the high-ranking and the low-rankingmales from each of the 10 flocks showed that high-ranking malesbegan singing earlier, sang longer, and sang at higher averageand maximum rates than low-ranking flockmates. Age of the maleshad less effect on song output at dawn than rank; older malestended to sing longer dawn choruses, but there was no differencein onset of singing, average song rate, or maximum song rateat dawn between hatch year and after-hatch year males. Our findingssuggest the dawn chorus can provide an accurate signal to femalesof the relative quality of their mate compared to neighboringmales     

Seasonal and diurnal patterns of black-capped chickadee (Poecile atricapillus) vocal production

Changes in vocal behaviour observed in temperate songbirds have been linked to changes in photoperiod. Research has focused on the fluctuation of hormones that lead to photosensitivity, photostimulation and photorefractoriness, as well as the 'dawn chorus' observed in numerous species. However, photoperiod in the natural environment is a complex event that occurs as seasons change. To determine the natural relationships between photoperiod and vocal behaviour we sampled vocal production of black-capped chickadees for three major vocal classes over one year at dawn, meridian and sunset. Fee-bee song production increased twice, once in the winter and once in the spring, and occurred almost exclusively at dawn. Chick-a-dee call production was highest in autumn and winter generally at the meridian. Gargle production did not differ significantly by season; however, the most gargle production occurred during the winter at the meridian.     

Food storage by black-capped chickadees: Memory for the location and contents of caches

Black-capped chickadees (Parus atricapillus) store food in a scattered distribution in their winter home range. Several hundred food items may be stored in a day, each in a separate cache site. Previous studies of marsh tits (Parus palustris) and nutcrackers (Nucifraga spp.) have shown that spatial memory is used to relocate caches. Memory for storage sites, if used by black-capped chickadees, is predicted to have four properties. Birds should be able to: (1) accurately relocate cache sites, (2) recall which caches they have previously emptied, (3) recall which sites they have discovered empty (as a result of loss to other animals) and (4) recall what type of food is stored at a cache site. Laboratory experiments show that chickadees do incorporate these kinds of information in memory for cache sites.     

The costs of immunological challenge to developing mountain chickadees, Poecile gambeli, in the wild

The tradeoff between immunocompetence and development in avian species could have long-term consequences relating to fitness. This study investigated the developmental cost of mounting a humoral immune response in growing mountain chickadees, Poecile gambeli . We immunologically challenged nestling chickadees using nonpathogenic antigens of either Newcastle disease virus vaccine or sheep red blood cells. Body mass, tarsal length, haematocrit, total plasma protein, and survival did not vary significantly between antigen treatment groups and control groups. Developmental stability was assessed using fluctuating asymmetry (FA) between the right and left ninth primary feather length. FA was increased significantly in the antigen-challenged birds. This result indicates that the up-regulation of the humoral immune response was developmentally costly to the nestlings by causing an increase in FA.     

Photoperiodic regulation of food storing and hippocampus volume in black-capped chickadees, Poecile atricapillus

In seasonal environments animals organize their behaviour around annual cycles of resource availability. Wild black-capped chickadees are most likely to hoard food in autumn. At this time of year chickadees are also reported to have a larger hippocampus, a brain area important for spatial memory. This study examined how photoperiodic condition affects these seasonal changes. Captive chickadees were exposed to one of three treatments. Photorefractory birds were held on long days (19:5 h light:dark) and had small gonads. Photosensitive birds were held on short days (LD 9:15 h) and also had small gonads. Photostimulated birds were switched from short to long days and quickly entered breeding condition with large gonads. Photosensitive birds (on short days) stored more seeds than photorefractory birds (on long days). Photostimulated birds stored seeds at a high rate when on short days, but reduced storing when transferred to long days. These results indicate that long days inhibit storing regardless of gonadal condition. There were no differences between groups in hippocampal volume, indicating that photoperiod can produce changes in food-storing behaviour without affecting hippocampal size. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.     

Patterns of extrapair mating in relation to male dominance status and female nest placement in black-capped chickadees

In sexually promiscuous animals, females may benefit by nestingclose to the edge of their partner's territory to facilitateextrapair copulations. In the present study, we describe theextrapair mating system of black-capped chickadees, Poecileatricapillus, and test whether nest locations are influencedby conspecific attraction to extrapair partners. We conducteda spatial analysis of female mating strategies by using microsatellitepaternity analysis in conjunction with geographic informationsystem (GIS) analysis of nest and territory locations. Extrapairoffspring comprised 52 of 351 offspring (14.8%) and were presentin 19 of 57 broods (33.3%). Females paired to males with lowdominance status in the previous winter's flock hierarchy weremore likely to engage in a mixed reproductive strategy thanwere females paired to males with high dominance status. Femaleshad extrapair copulations and extrapair fertilizations withhigh-ranking males more often than with low-ranking males. Notall extrapair copulations resulted in extrapair fertilizations.Females constructed their nests within 16.8 ± 1.0 m ofthe edge of their partner's territory, significantly closerto the edge of their nearest neighbor's territory than to thecenter of their own partner's territory. Extrapair males usuallyshared territory boundaries with cuckolded males. Females pairedto low-ranking males constructed nests near the territory edgesof neighboring high-ranking males. However, females did nothave extrapair copulations with the neighbor nearest to theirnest or even with the high-ranking neighbor nearest to theirnest. We conclude that conspecific attraction to neighbors mayinfluence nesting location in black-capped chickadees; however,it does not operate by facilitating extrapair copulations.