Urban tolerance of birds changes throughout the full annual cycle

Abstract

Aim: As urban areas continue to expand, it is increasingly important to quantify species-specific responses to urban environments, and how these change across the full annual cycle. Our objective was to quantify urban tolerance for North American birds across the time. We tested (a) whether intra-annual variability of urban tolerance differed between migrants and residents and (b) whether intra-annual variability of urban tolerance was phylogenetically conserved. We then assessed how the relationship between ecological and life history traits and urban tolerance differed both across the year and between migrants and residents.Location: North America.Taxon: Birds. Methods:We integrated a large citizen science dataset of observations for 237 bird species, remotely sensed VIIRS night-time lights data, and trait data on each species.We estimate, for each species and each month of the year, a continuous measure of urban tolerance (i.e. the median of their distribution of observations across an urbanization gradient). We then use phylogenetic linear models to assess the relationship between this measure of urban tolerance and various life history and ecological traits.Results: There was a distinct drop in the overall urban tolerance scores corresponding with the breeding period; this pattern was more pronounced for migrants compared to residents. Migrants also had greater intra-annual variability than resident species.We also found that the strength of the relationships between ecological and life history traits and urban tolerance was highly seasonal for most traits considered, and some divergent patterns were noted between migrants and residents. Main conclusions:The urban tolerance of birds greatly changed throughout the annual cycle, with different patterns for migrants and residents. Compared to residents, migrants showed more intra-annual variability of urban tolerance with a drop in the average urban tolerance score during the breeding season. Together, our results suggest that urban tolerance is a function of both species and season, and they highlight the importance of considering the dynamic nature of birds' use of urban ecosystems throughout the full annual cycle.

Taxonomic, Phylogenetic and Functional Diversity of Bird Assemblages in Urban Green Spaces: Null Model Analyses, Temporal Variation and Ecological Drivers

“…This is noteworthy considering that others have found that predictors can have contrasting effects among seasons (La Sorte et al, 2020). We propose that temporal changes in the strength of the diversity-environment relationships can be the result of mechanisms simultaneously operating such as changes in anthropogenic food availability (Stofberg et al, 2019), the seasonal use of habitat (Marone et al, 1997), the species urban tolerance (Callaghan et al, 2021), and the anthropic related mortality (Bracey et al, 2016) among others.…”

Urban affinity and its associated traits: A global analysis of bats

“…Recently, an adjustment of urban affinity indices that aims to account for the potential effects of range size, sampling biases and interspecific competition has been published and provides a potential solution for biased data (Callaghan, Cornwell, et al, 2021;Callaghan, Major, et al, 2020). In any case, the scores of the indices we present should not be interpreted as absolute but as relative values of urban affinity that allow comparing different indices and species with each other but do not necessarily reflect the actual urban affinity.…”

“…Callaghan et al, 2019;Hill et al, 2002). Another interesting possibility to extend the application of the indices would be to add a temporal component, that is, to track changes in the urban affinity in the course of a year (Callaghan, Cornwell, et al, 2021) or over longer time periods. The latter could help to detect long-term effects of urbanization.…”

Taxonomic and functional homogenization of farmland birds along an urbanization gradient in a tropical megacity

“…These spatial patterns were consistent across the summer and the monsoon seasons, but not during winter (Figure S1), where the higher dissimilarity may result from an increased number of overwintering visitors. Indeed, it has been demonstrated that urban tolerance changes through the year with different patterns for migratory and breeding/resident species (Callaghan et al, 2021).…”