Sperm head abnormalities are associated with excessive omega-6 fatty acids in two finch species feeding on sunflower seeds

In a rapidly changing world, it is important to understand how urban environments impact wildlife. For example, supplementary feeding of birds, though well‐intended, might have unexpected negative effects on the health of individual animals. Sunflower seeds are commonly provided in garden bird feeders, but they contain high levels of linoleic acid (LA), an omega‐6 polyunsaturated fatty acid (PUFA). Omega‐6 PUFAs are associated with increased oxidative stress, which can damage cell membranes, and in particular sperm cells. We assessed the level of LA in the blood of two seed‐eating finch species, greenfinches Chloris chloris and hawfinches Coccothraustes coccothraustes, caught in 2015 and 2017 in environments with direct access to sunflower seed feeders (Norway), and compared these with the level of LA in a smaller number of individuals sampled in 2015 in a rural area with low incidence of sunflower seed feeders (Czech Republic). Furthermore, we investigated the relationship between the ...