Influence of urbanization on body size, condition and physiology in an urban exploiter: a multi-component approach
Résumé
Consistent expanding urbanization dramatically transforms natural habitats and exposes
organisms to novel environmental challenges, often leading to reduced species richness
and diversity in cities. However, it remains unclear how individuals are affected by the urban
environment and how they can or cannot adjust to the specific characteristics of urban life
(e.g. food availability). In this study, we used an integrative multi-component approach to
investigate the effects of urbanization on the nutritional status of house sparrows (Passer
domesticus). We assessed several morphological and physiological indices of body condition
in both juveniles (early post-fledging) and breeding adults from four sites with different
levels of urbanization in France, Western Europe. We found that sparrows in more urbanized
habitats have reduced body size and body mass compared to their rural conspecifics.
However, we did not find any consistent differences in a number of complementary indices
of condition (scaled mass index, muscle score, hematocrit, baseline and stress-induced
corticosterone levels) between urban and rural birds, indicating that urban sparrows may
not be suffering nutritional stress. Our results suggest that the urban environment is unlikely
to energetically constrain adult sparrows, although other urban-related variables may constrain
them. On the other hand, we found significant difference in juvenile fat scores, suggesting
that food types provided to young sparrows differed highly between habitats. In
addition to the observed smaller size of urban sparrows, these results suggest that the
urban environment is inadequate to satisfy early-life sparrows’ nutritional requirements,
growth, and development. The urban environment may therefore have life-long consequences
for developing birds.