# Links between fear of humans, stress and survival support a non-random distribution of birds among urban and rural habitats

## TL;DR

Birds in urban areas show similar stress levels to rural birds but higher survival, suggesting they self-select habitats based on their tolerance to human presence.

## Contribution

The study links behavioral traits, stress, and survival to explain non-random habitat distribution in urban and rural birds.

## Key findings

- Urban birds had shorter flight initiation distances but similar corticosterone levels to rural birds.
- Survival was twice as high in urban birds compared to rural ones.
- Corticosterone and survival showed a quadratic relationship in urban birds but not in rural ones.

## Abstract

Urban endocrine ecology aims to understand how organisms cope with new sources of stress and maintain allostatic load to thrive in an increasingly urbanized world. Recent research efforts have yielded controversial results based on short-term measures of stress, without exploring its fitness effects. We measured feather corticosterone (CORTf, reflecting the duration and amplitude of glucocorticoid secretion over several weeks) and subsequent annual survival in urban and rural burrowing owls. This species shows high individual consistency in fear of humans (i.e., flight initiation distance, FID), allowing us to hypothesize that individuals distribute among habitats according to their tolerance to human disturbance. FIDs were shorter in urban than in rural birds, but CORTf levels did not differ, nor were correlated to FIDs. Survival was twice as high in urban as in rural birds and links with CORTf varied between habitats: while a quadratic relationship supports stabilizing selection in urban birds, high predation rates may have masked CORTf-survival relationship in rural ones. These results evidence that urban life does not constitute an additional source of stress for urban individuals, as shown by their near identical CORTf values compared with rural conspecifics supporting the non-random distribution of individuals among habitats according to their behavioural phenotypes.