Urban-nesting mountain chickadees have a reduced response to a simulated predator

Anti-predator behaviour is common among birds, but little research exists on whether differences in the predator landscape between urban and rural habitats results in differential anti-predator behaviour. We compared nest-defence behaviour of mountain chickadees (Poecile gambeli) in urban and rural habitats in Kamloops, BC, Canada to a simulated predator model (snake) on top of nest boxes while incubating females were away from nests on foraging bouts. Upon their return, we recorded proximity to the predator model, latency to contact the nest box and enter the nest, and number of gargle and chick-a-dee calls as measures of anti-predator behaviour and compared multivariate “predator aversion scores” across birds occupying either rural or urban landscapes. Rural-nesting birds had more aversive reactions to the predator model than the urban-nesting birds, which may suggest differences in perceived threat of the model, in combination with increased boldness associated with urban-nesting birds.

Analysis of Mountain Chickadee (Poecile gambeli) associated bacterial communities across urban and rural habitats

Host associated microbial communities play important roles in wildlife health, but these dynamics can be influenced by environmental factors. Urbanization has numerous consequences on wildlife; however, the degree to which wildlife associated bacterial communities and potential bacterial pathogens vary across urban to rural/native habitat gradients remains largely unknown. We used 16S rRNA gene amplicon sequencing to examine bacterial communities found on mountain chickadee (Poecile gambeli) feathers and nests in urban and rural habitats. Feathers and nests in urban and rural sites had similar abundances of major bacterial phyla and dominant genera with pathogenic members. However, richness of bacterial communities and potential pathogens on birds were higher in urban habitats, and potential pathogens accounted for some of the differences in bacterial occurrence between urban and rural environments. We predicted habitat using potential pathogen occurrence with a 90% success rate for feather bacteria, and a 72.2% success rate for nest bacteria, suggesting an influence of urban environments on potential pathogen presence. We additionally observed similarities in bacterial communities between nests and their occupants, suggesting bacterial transmission between them. These findings improve our understanding of the bacterial communities associated with urban wildlife and suggest that urbanization may impact wildlife associated bacterial community compositions.

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.

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.