Does the Urban Environment Act as a Filter on the Individual Quality of Birds?

Abstract

Phenotypic divergences of birds are common between urban and natural habitats and can result from different selective pressures between habitats or maladaptation to the city. No uniform patterns were observed, especially concerning markers of bird health, such as, for example, telomere length. Telomeres are involved in maintaining genome integrity and naturally shorten with age, but environmental stressors can accelerate their attrition. Thus, telomere length can be an indicator of individual quality. Some studies showed that urban breeders had longer telomeres than forest individuals. Two hypotheses can explain this result: (1) urban breeders are younger than forests breeders, and (2) cities act as a filter on individuals and only high-quality birds can successfully reproduce. In this context, we compared the age category (molting pattern) and morphological and physiological characteristics of urban and forest Great Tits before and during breeding. No differences in age or body condition were observed. However, urban breeders were smaller and had shorter telomeres than birds captured in winter. Urban birds had longer telomeres than forest birds, only in winter. These results highlight that urban habitats potentially favor smaller birds. However, the decrease in telomere length between winter and reproduction only in the city suggest a higher cost of reproduction in the city compared to the forest.

Telomere length vary with sex, hatching order and year of birth in little owls, Athene noctua

“…Differences in telomere length in relation to gender has been previously illustrated in several taxa (reviewed in Barrett & Richardson, 2011), and particularly in birds with sex-biased body size or investment in reproduction, with no consensual general pattern (e.g. Caprioli et al, 2013;Remot et al, 2020;Saulnier et al, 2022 for no sex differences) (e.g. Bauch et al, 2020 for sex differences).…”

Telomere length varies with sex, hatching rank and year of birth in the Little Owl, Athene noctua

“…Differences in telomere length in relation to sex has been previously illustrated in several taxa (reviewed in Barrett & Richardson, 2011), and particularly in birds with sex-biased body size or investment in reproduction, producing no consistent male-female differences (e.g. Caprioli et al, 2013;Remot et al, 2020;Saulnier et al, 2022 for no sex differences) (e.g. Bauch et al, 2020 for sex differences).…”