Abstract
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.
Highlights
Pressures that human activities exert on the environment are steadily increasing and substantially affect ecosystem function [1]
Urbanization, Body Condition, and Avian Stress Physiology species seem to benefit from the urban environment (“urban exploiters”), many others seem unable to persist in cities (“urban avoiders”), and as a result, species richness and diversity overall is low in urban areas, especially for avian communities [3,4,5,6]
In addition to the SMI, we investigated complementary indices of body condition that all led to the same conclusion, strongly suggesting that urban sparrows are not suffering from nutritional stress
Summary
Pressures that human activities exert on the environment are steadily increasing and substantially affect ecosystem function [1]. Urbanization exposes organisms to novel environmental challenges because of the specific characteristics of urban environments (e.g., resource availability, micro-climate, species interactions, disturbances, pollution; [7,8,9,10,11,12,13]). The modified environmental conditions of urban environments expose organisms to new selective pressures that are likely to affect wild vertebrates. Because the ability to successfully adapt to urban-related environmental changes can vary with species’ ecological and life history traits (e.g., dispersal ability, behavioral flexibility, diet, stress tolerance, annual fecundity [15,24,25]), organisms’ responses to urbanization differ highly among species. In a rapidly urbanizing world, it is crucial to understand how free-living organisms are affected by the urban environment, and how they can or cannot adjust to its constraints
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