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.

Avian communication networks: how audible are mountain chickadee males during dawn signalling?

My thesis investigates how urban noise influences the relative audibility of songs to female Mountain Chickadees (Poecile gambeli), who assess male signalling at dawn while roosting within the nest cavity. Over two breeding seasons, I monitored Mountain Chickadees breeding on an urban/rural interface in Kamloops, BC, Canada. I broadcast typical Mountain Chickadee songs, with or without added noise, towards recently unoccupied nests while simultaneously re-recording these songs with microphones outside and inside the nest box to determine the relative audibility in relation to both distance and presence/absence of noise. I then tracked individual males’ behaviour and movement during dawn signalling, while passively recording their songs with microphones — outside and inside the nest box — to determine the relative audibility of signals from the perspective of the roosting female. The relative audibility of songs decreased with increasing distance from the nest, which was compounded by increased urban noise. During dawn signalling, urban males respond to these effects by remaining closer to the nest, resulting in their songs being more audible within the nest than their rural counterparts. Overall, ambient noise and distance had an interactive effect on relative audibility of songs, suggesting complex dynamics of communication networks that may result in a trade-off, where males are forced to prioritize directing their signals to either their social mates or neighbours.

Effects of parental condition and nesting habitat on sex allocation in the mountain chickadee

When the reproductive value of sons vs. daughters differs, sex allocation theory predicts females should bias the sex ratio of their broods towards the higher-value sex. Females in numerous bird species appear to bias offspring sex in response to self and mate condition, and breeding habitat quality. Over three breeding seasons, we monitored mountain chickadees breeding along a rural to urban habitat gradient. We did not find female condition or the condition of the putative father or true genetic father to influence offspring sex. We found marginal evidence for sex allocation in relation to habitat urbanization, though opposite to our predictions. In urban habitat, offspring were more likely to be female as the degree of habitat urbanization increased. We suggest habitat quality may be influential in mountain chickadee reproductive decisions; however, the ecology of mountain chickadees may not fulfill the assumptions of sex allocation theory.

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.