Urbanization and elevated cholesterol in American crows

Although urban areas can be sources of abundant food for wildlife, anthropogenic foods may be lower in quality than natural food sources. Overall, the consequences of anthropogenic food consumption for wildlife are poorly understood. Here, we examined how urbanization and anthropogenic food were linked to cholesterol, condition, and survival of American crows (Corvus brachyrhynchos). We collected cholesterol and landscape data from 140 crow nestlings along an urban to rural gradient in Davis, CA, USA, and we ran a supplementation experiment with high-cholesterol fast food (McDonald’s cheeseburgers) on 86 nestlings in a rural population in Clinton, NY, USA. We used these data to evaluate links between cholesterol level, urbanization, condition, and crow survival. We found that plasma cholesterol increased with percentage of impervious surface along the urban to rural gradient. Cholesterol levels were sensitive to anthropogenic foods: crows supplemented with fastfood cheeseburgers had higher cholesterol levels than unsupplemented crows. Elevated cholesterol levels had no detectable effects on survival and were associated with higher indices of body condition, although urbanization itself was linked to lower survival. Elevated cholesterol levels could indicate access to high-calorie, high-fat anthropogenic foods, which might, in some contexts, improve body condition, potentially offsetting other negative effects of urbanization. Observations over a longer time-scale, assessing additional indices of health and fitness, are needed to evaluate long-term costs or benefits of elevated cholesterol for urban crows.