Generalists are the most urban-tolerant birdsSubmitted by editor on 1 February 2019.Get the paper!
What makes an urban bird (Figure 1)? Are there certain ecological and life history traits which make some species predisposed to urban living (Figure 2)? This is a longstanding question in urban ecology: see here, here, and here for just a few select examples. Much of the previous research has focused on a priori grouping of species based on their relatively qualitative response to urbanization: urban avoiders, urban adapters, and urban exploiters are a common example.
Figure 1: Some species, like this Noisy Miner have adapted to urbanization and associated humans to such an extent they share similar tastes in beverages! Noisy Miner was relatively more urban than the rest of the honeyeaters included in the analysis. Photo: Corey T. Callaghan
Figure 2: Some birds have the ability to persist, despite the damage caused by the human population: a potentially hazardous aspect of urbanization. Photo credit: Corey T. Callaghan
We extend the previous methods by using a species-specific approach to assign individual species ‘scores’ based on their response to urbanization. To do this, we integrate broad-scale eBird data with VIIRS night-time lights data. We then look at a species-specific distribution in response to the night-time lights data – a continuous proxy of urbanization (Figure 3). A species’ urban score was defined as the median of their distribution. We did this for 477 species, relying on > 5 million bird observations.
Figure 3: Five selected examples of species-specific distributions in response to urbanization. Photo credits: Corey T. Callaghan
Our analysis investigated non-phylogenetic and phylogenetic relationships and there was a significant pattern of response to urbanization, phylogenetically (Figure 4). We provide a web-app which allows people to investigate species’ scores on a phylogenetic tree (https://johnwilshire.github.io/bird_urbanness_web_app/).
Fogure 4: The phylogenetic tree, showing the urbanization score 477 species in Australia, represented by the length of the bar as well as the color. Drawings by Corrine Edwards.
The final step to our analysis was to integrate a third dataset: a dataset consisting of ecological, biological, and life history traits for Australian birds. We used these data to assess which species’ traits are most likely to influence their response to urbanization – measured as their urbanization scores explained above.
We found that the most urban-tolerant species in our analyses had large niche breadths and were generalist species. This means that specialist species are potentially most at-risk to the impacts of urbanization. Our findings: (1) provide generalizable methods while (2) informing our knowledge of species’ traits and how they influence species-specific responses to urbanization. Urban-intolerant species, and their life history strategies, need to be carefully managed for with increasing urbanization.
Corey T. Callaghan on behalf of all co-authors.