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

More Mountain Chickadees (Poecile gambeli) sing atypical songs in urban than in rural areas

Urbanization results in novel ecosystems with unique challenges. These may lead to problems during song learning or development and could result in the singing of atypical songs. During studies of Mountain Chickadees (Poecile gambeli) and urbanization in British Columbia, Canada, we observed males singing atypical songs along an urbanization gradient. We found that eight of 78 males consistently sang atypical songs and the odds of singing atypical songs increased with urbanization. We explored several explanations including habitat quality, population density, and bioacoustics. Future studies investigating causes and consequences of atypical singing will clarify effects of urbanization on Mountain Chickadees

Supplemental feeding may reduce responsiveness of Black-capped Chickadees (Poecile atricapillus) to avian mobbing calls during gap-crossing experiments

Deforestation creates gaps in forest habitat, which can limit the movements of many avian species. Increased predation risk associated with crossing open habitats is often considered the primary impediment to crossing gaps. However, other factors such as energetic reserves may also influence these decisions. We conducted playback experiments before and after supplemental feeding of Black-capped Chickadees (Poecile atricapillus (Linnaeus, 1766)) to investigate how energetic reserves influenced gap-crossing decisions. Black-capped Chickadees were less likely to respond to playbacks, whether conducted within forests or across gaps, after supplemental feeding. This suggests that energetic reserves may have less influence on gap-crossing decisions than on the willingness of birds to respond to mobbing calls in general. We recommend that future studies investigating gap-crossing decisions using playbacks account for differences in resource availability among sampling locations, especially when making comparisons across discrete habitats.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Rapid advancement of spring migration and en route adjustment of migration timing in response to weather during fall migration in Vaux’s Swifts (Chaetura vauxi)

Climate change has generated earlier springs, later falls and different weather patterns. These changes may prove challenging to migratory species if they are unable to adjust their migratory timing. We analyzed changes in migratory timing of Vaux’s Swifts (Chaetura vauxi Townsend 1839) by examining first arrivals (date the first swift arrived) and peak roost occupancy (date the maximum number of swifts were observed) at migratory roosts in both spring and fall from the citizen science organization Vaux’s Happening. First arrivals and peak occupancy date in Vaux’s Swifts advanced over time from 2008-2017, and the timing of first arrivals advanced with an increase in local wind gust speeds. In contrast, fall migration timing did not change over time from 2008-2016, but higher temperatures were associated with later fall migration (both first arrival and peak roost occupancy) and higher local wind speeds were associated with earlier fall migration (peak roost occupancy only). Like many other migratory birds, Vaux’s Swifts may be tracking earlier spring phenology, and may also be altering their migratory timing in response to local weather conditions, especially during fall migration. Our results indicate that swifts may be able to adjust their migration to a changing climate, at least in the short term.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Extrapair paternity and mate choice in a chickadee hybrid zone

The dynamics of hybrid zones are likely to be influenced greatly by patterns of mate choice, including "cryptic" choice mediated through extrapair copulations. To understand changes in hybrid zones over time and space, a detailed examination of mating patterns and correlates is needed. We studied the role of extrapair fertilizations (EPFs) in the breeding biology of hybridizing black-capped and Carolina chickadees in southeastern Pennsylvania over 4 years, using microsatellite DNA markers. We detected extrapair offspring (EPO) in 56% of 90 broods examined; these accounted for at least 26% of 477 offspring. Chickadees do not appear to use EPFs to reduce costs of heterospecific pairing: EPFs were no more likely to occur in genetically dissimilar (heterospecific) social pairs than in pairs where social mates were genetically similar. However, females paired with black-capped--like males were more likely to have EPO. Females that acquired EPFs did not obtain these from males genetically similar to themselves; instead, all females, regardless of their genotype or that of their social mate, tended to prefer Carolina-like males as extrapair partners. There was no relationship between the presence of EPO and hatching or fledging success. High rates of extrapair paternity and apparent female preference for Carolina-like males suggest that mate choice is an important influence in ongoing northward movement of this hybrid zone. Copyright 2006.chickadee; extrapair; hybrid; mate choice; paternity; poecile