Eating in the city: Experimental effect of anthropogenic food resources on the body condition, nutritional status, and oxidative stress of an urban bioindicator passerine

Abstract

Urban areas provide a constant and predictable supply of anthropogenic processed food. The House Sparrow (Passer domesticus Linnaeus, 1758), a declining urban bioindicator species, has recently been reported to have a high level of oxidative stress, with urban diet or pollutants proposed as the potential cause. In this study, we aimed to experimentally determine the effects of two urban trophic resource types (bar snack food leftovers and pet food) on sparrows' physical condition, plasma biochemical nutritional parameters, and blood oxidative status in captivity. To exclude the potential previous effect of urban pollutants, 75 House Sparrows were captured from a rural area in SE Spain and kept in outdoor aviaries. Individuals were exposed to one of three diet treatments: control diet (fruit, vegetables, poultry grain mixture), bar snack diet (ultra‐processed snacks), or cat food diet (dry pellets) for 20 days. Blood samples were collected before and after diet treatments to analyze the relative change rates of 12 variables, including physical condition, nutritional status, and oxidant–antioxidant status. A principal component analysis was run to identify gradients of variables covariation, and Generalized Linear Mixed Models were used to determine the effect of diets on each selected PC and on raw variables. The bar snack diet led to signs of anemia and malnutrition, and females tended to lose body condition. The cat food diet increased oxidative stress indicators and protein catabolism. Unbalanced urban diets can affect the body condition and nutritional physiology of House Sparrows and may also induce oxidative stress despite the absence of environmental pollution.

Contrasting morphometric responses to increasing urbanisation in congeneric sparrow species

“…Nevertheless, both resource quality and availability (i.e., the credit-card hypothesis) 37 and thermoregulatory responses (i.e., Bergmann’s rule) 39 may play a role in the response of the Cape Sparrow to urbanisation. The smaller size of the Cape sparrows in increasingly urbanised systems suggests that the lower quality of resources 38 and warmer urban climates induce physiological and thermoregulatory stresses linked to their water use and energy reserves 71 . Reduced mass and size may help combat these constraints in highly urbanised areas, whereas increased urban vegetation may buffer the effects, resulting in larger Cape sparrows within more vegetated urban systems 72 .…”

“…First, the credit-card hypothesis 37 , which proposes a decrease in the body mass, body condition and body plan (i.e., concurrent and multidirectional changes across a bird’s wing, tarsus, and tail lengths) within increasingly urbanised systems. This hypothesis is strongly linked to decreased resource quality and the availability of novel food resources of lower nutritional quality (e.g., discarded food waste) 38 . These novel resources cause a reduction in individual fat reserves and subsequently lower reproductive output 37 .…”

Short-term dietary changes are reflected in the cerebral content of adult ring-billed gulls

“…Several species thrive in urban environments, in part, because they have access to abundant and consistent anthropogenic food resources [1][2][3]. Yet, anthropogenic foods often lack nutritional quality, potentially causing nutritional deficiencies in essential amino acids, fatty acids or micronutrients [4][5][6]. Western diets are notably deficient in omega-3 fatty acids (n3-PUFAs), which include the medium-chain alpha-linolenic acid (ALA) and its long-chain derivates omega-3 long-chain polyunsaturated fatty acids (n3-LCPUFAs), namely eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) [7,8].…”