Nest-Site Selection by Female Black-Capped Chickadees: Settlement Based on Conspecific Attraction?

Female Black-capped Chickadees (Poecile atricapillus) solicit extrapair copulations (EPCs) from neighboring high-ranking males, and these EPCs result in extrapair young. Females might choose to locate their nests near the territory boundaries of attractive males to facilitate access to EPCs. Other hypotheses might also explain choice of nest site, namely (1) habitat characteristics, (2) prey abundance, and (3) previous experience. We tested these four hypotheses in 1996 and 1997. Out of 27 habitat characteristics measured, we found only one that was significantly different between nests and control sites in both years. The abundance of large trees was lower at nest sites than at control sites in each year and when years were pooled. Relative prey abundance did not differ between nests and control sites for either year of the study. We found no different in interyear nest placement based on female experience; experienced females nester farther than 60 m from their previous nest sites in both years of the study. In 1996, females whose neighboring males were higher ranked than their social partner located their nests significantly closer to territory boundaries than did females whose nearest neighbors were lower ranked than their social partner. In 1997, all pairs nested near territory boundaries. We conclude that choice of nest location in Black-capped Chickadees is influenced by conspecific attraction based on mating tactics

Presence of Cavities in Snags Retained in Forest Cutblocks: Do Management Policies Promote Species Retention?

Tree cavities, which are frequently excavated by primary cavity nesters, are typically used by a number of avian and non-avian species and are thus important components in maintaining biodiversity in forest ecosystems. One way to provide these habitat opportunities in harvested areas is through the retention of snags. In this study, we assessed the habitat and snag characteristics that promote cavity excavation, using the presence of cavities to infer activity of primary cavity excavators. Snags retained closer to the forest/cutblock edge contained a greater density of cavities than trees further from edge. However, the proportion of cavities found within cutblocks declined at a more rapid rate with distance from edge than did those in adjacent forested stands. There was also a tendency for cavities to occur more frequently in trees that were at the advanced stages of decay. The results of our study suggest management for snags in harvest areas should include the retention of snags closer to the forest edge combined with incorporating trees showing signs of advanced decay

Sympatric song variant in mountain chickadees Poecile gambeli does not reduce aggression from black-capped chickadees Poecile atricapillus

When habitats overlap and species compete for resources, negative interactions frequently occur. Character displacement in the form of behavioural, social or morphological divergences between closely related species can act to reduce negative interactions and often arise in regions of geographic overlap. Mountain chickadees  Poecile gambeli have an altered song structure in regions of geographic overlap with the behaviourally dominant black capped chickadee Poecile atricapillus. Similar to European and Asian tits, altered song in mountain chickadees  may decrease aggression from black-capped chickadees. To test this hypothesis, we conducted a playback study in Prince George, BC, Canada, to examine how black-capped chickadees responded to the songs of mountain chickadees recorded in regions where the two species were either sympatric or allopatric. We used principal  component analysis (PCA) to collapse behavioural response variables into a single ‘approach’ variable and a single ‘vocalisation’ variable. We then used mixed-model analysis to determine whether there was a difference in approach or vocalisation response to the two types of mountain chickadee songs (allopatric  songs and variant sympatric songs). Black-capped chickadees responded with equal intensity to both types of mountain chickadee songs, suggesting that the variant mountain chickadee songs from regions of sympatry with black-capped chickadees do not reduce heterospecific aggression. To our knowledge, this is the only instance of a character shift unassociated with reduced aggression in the family Paridae and raises interesting questions about the selective pressures leading to the evolution of this song divergence

Between-Year Survival and Rank Transitions in Male Black-Capped Chickadees (\u3cem\u3ePoecile Atricapillus\u3c/em\u3e): A Multistate Modeling Approach

In dominance-structured animal societies, variation in individual fitness is often related to social status. Like many passerine birds, Black-capped Chickadees (Poecile atricapillus) have a short average adult life-expectancy (Ø2 years); however, the maximum recorded life span is \u3e5× as long. Enhanced annual survival could contribute to greater lifetime reproductive success for male Black-capped Chickadees with high social rank. We used multistate capture–mark–recapture models to estimate annual survival of male Black-capped Chickadees in Ontario using resighting and recapture data collected from 1997 to 2002. Our goal was to evaluate support for an influence of rank on annual survival and estimate its effect size for a food-supplemented study site. We also statistically modeled the probability of between-year rank transitions. Model selection based on Akaike’s information criterion provided support for an effect of rank on survival. However, multimodel inference revealed that the size of the effect was rather small. Over the six study years, model-averaged estimates of the survival benefit of high versus low rank ranged from 5.0 to 7.3%. As expected, survival was strongly year-dependent, with model-averaged estimates of annual survival probability varying between 0.36 and 0.73. Age was an important predictor of the probability of rank transitions. Low-ranked second-year birds were less likely than older low-ranked birds to advance to high rank between years; likewise, high-ranked after-second-year birds were less likely to drop in rank. Other studies have found larger effects of rank on survival than we observed here. Future research should consider how interactions between social and environmental factors influence annual survival

Enhanced Reproductive Success of Female Black-Capped Chickadees Mated to High-Ranking Males

Overwinter survival of female Black-capped Chickadees (Poecile atricapillus) depends in part on the rank of their mates. We investigated whether females also gain reproductive beenfits by pairing with high-ranking males. We assessed breeding success in 1993 to 1995 and 1997 by comparing clutch size, proportion of eggs hatched, hatching date, and prediction rates on nests of females mated to either high-ranking or low-ranking males. We also compared feeding rates of males to incubating females and to offspring during the early nestling period in 1994 and 1995. High-ranking and low-ranking males did not differ in feeding rates during early incubation or early nestling stages. Females mated to high-ranking males incubated for longer periods than females mated ot low-ranking males. Younger males and females mated to low-ranking males fed nestlings at a higher rate than did older males and females mated to high-ranking males, respectively. Females mated ot high-ranking males had larger clutches, hatched a significantly greater proportion of their eggs, and suffered lower nest predation than females mated to low-ranking males. In 1995 and 1997, where the ranks and ages of both members of 23 pairs were known, female rank was strongly correlated with mate rank and age but was only weakly associated with female age. Female rank accounted for significant variation only in clutch size, and male rank accounted for a greater proportion of variation in clutch size and fleding success than did the female’s own rank

Enhanced Reproductive Success of Female Black-Capped Chickadees Mated to High-Ranking Males

Overwinter survival of female Black-capped Chickadees (Poecile atricapillus) depends in part on the rank of their mates. We investigated whether females also gain reproductive beenfits by pairing with high-ranking males. We assessed breeding success in 1993 to 1995 and 1997 by comparing clutch size, proportion of eggs hatched, hatching date, and prediction rates on nests of females mated to either high-ranking or low-ranking males. We also compared feeding rates of males to incubating females and to offspring during the early nestling period in 1994 and 1995. High-ranking and low-ranking males did not differ in feeding rates during early incubation or early nestling stages. Females mated to high-ranking males incubated for longer periods than females mated ot low-ranking males. Younger males and females mated to low-ranking males fed nestlings at a higher rate than did older males and females mated to high-ranking males, respectively. Females mated ot high-ranking males had larger clutches, hatched a significantly greater proportion of their eggs, and suffered lower nest predation than females mated to low-ranking males. In 1995 and 1997, where the ranks and ages of both members of 23 pairs were known, female rank was strongly correlated with mate rank and age but was only weakly associated with female age. Female rank accounted for significant variation only in clutch size, and male rank accounted for a greater proportion of variation in clutch size and fleding success than did the female’s own rank

Between-year survival and rank transitions in male black-capped chickadees (Poecile atricapillus): A multistate modeling approach

In dominance-structured animal societies, variation in individual fitness is often related to social status. Like many passerine birds, Black-capped Chickadees (Poecile atricapillus) have a short average adult life-expectancy (∼2 years); however, the maximum recorded life span is \u3e 5× as long. Enhanced annual survival could contribute to greater lifetime reproductive success for male Black-capped Chickadees with high social rank. We used multistate capture-mark-recapture models to estimate annual survival of male Black-capped Chickadees in Ontario using resighting and recapture data collected from 1997 to 2002. Our goal was to evaluate support for an influence of rank on annual survival and estimate its effect size for a food-supplemented study site. We also statistically modeled the probability of between-year rank transitions. Model selection based on Akaike\u27s information criterion provided support for an effect of rank on survival. However, multimodel inference revealed that the size of the effect was rather small. Over the six study years, model-averaged estimates of the survival benefit of high versus low rank ranged from 5.0 to 7.3%. As expected, survival was strongly year-dependent, with model-averaged estimates of annual survival probability varying between 0.36 and 0.73. Age was an important predictor of the probability of rank transitions. Low-ranked second-year birds were less likely than older low-ranked birds to advance to high rank between years; likewise, high-ranked after-second-year birds were less likely to drop in rank. Other studies have found larger effects of rank on survival than we observed here. Future research should consider how interactions between social and environmental factors influence annual survival. © The American Ornithologists\u27 Union, 2008

Do phylogeny and habitat influence admixture among four North American chickadee (family: Paridae) species?

Accepted author manuscriptHybridization is an important aspect of speciation, yet questions remain about the ecological and environmental factors that influence hybridization among wild populations. We used microsatellite genotyping data and collected land cover and environmental data for four North American chickadee species: black-capped Poecile atricapillus, mountain P. gambeli, chestnut-backed P. rufescens and boreal P. hudsonicus chickadees. Combining these datasets, we sought to examine whether there is evidence of admixture between four widely distributed North American chickadee species; whether admixture takes place more often between more closely related species pairs or between species pairs with more similar ecological preferences; and whether certain habitat types have higher rates of admixture than others. We detected admixture for five of the six species pairs analyzed (chestnut-backed–mountain chickadee pair showed no evidence of admixture), and found rates of admixture varied geographically, and within taxa pairs. Admixture was higher among less closely related species than more closely related species, although habitat similarity was not a significant predictor. Finally, rates of admixture were higher in urban parkland habitats than deciduous, mixed or coniferous forest habitats. Our work indicates admixture occurs frequently among North American parids, and habitat and environmental variation may play an important role in the frequency and geographic distribution of hybridization.Ye

Grass Management Regimes Affect Grasshopper Availability and Subsequently American Crow Activity at Airports

With large expanses of open vegetation, airports serve as major attractants for numerous bird species, such as the American crow (Corvus brachyrhynchos), which can lead to high risk of bird–aircraft collision. Previous observations of large influxes of crows at the Prince George Airport (British Columbia, Canada) in July and August suggested that crows were opportunistically foraging on grasshopper (Melanoplus sp.) population eruptions in mown grass during those months. We tested whether grasshoppers were more visible (i.e., easier for crows to detect) under different grass lengths, and whether crows were preferentially attracted to these same grass lengths. Employing line transects during July to August 2010 and 2011, we detected \u3e6 times as many grasshoppers in short-cut grass (0 to 15 cm) than in uncut grass (\u3e30 cm). Data from 2011 also revealed that grasshopper detections by crows was significantly higher in short-cut grass than in grass left at intermediate lengths (long-cut grass [15 to 30 cm]). Crow densities also varied with grass length, with significantly more crows foraging in short-cut than long-cut or uncut grass lengths. Our results indicate that allowing the grass to grow to \u3e15 cm could reduce the attraction of crows to the airfield and may reduce bird–aircraft collisions