Urban living influences the reproductive success of Darwin’s finches in the Galápagos Islands

Urbanization is expanding worldwide and can have major consequences for organisms. For example, urban areas can contain novel stressors that reduce the fitness of animals but may also have benefits, such as consistent human food availability. These trade-offs are particularly important in dynamic environments with unreliable annual natural food availability, such as in the Galapagos Islands. In our study, we compared the reproductive success of small ground finches (Geospiza fuliginosa; a species of Darwins finch) in an urban and non-urban area during a dry year (i.e. one with low natural resource availability) on San Cristobal Island in the Galapagos Islands. We also documented the abundance of anthropogenic-related material, such as human hair and plastic, in finch nests and determined whether incorporating these materials into the nest led to entanglement- or ingestion-related mortalities. Overall, urban finches built more nests, laid more eggs, and produced more nestlings than non-urban finches. However, every nest in the urban area contained anthropogenic-related material, which resulted in four mortalities (out of 17 nests with nestlings) due to entanglement or ingestion. Non-urban nests did not contain any anthropogenic-related material. Our study showed that urban living has trade-offs: urban birds have overall higher reproductive success than non-urban birds, but urban birds can also suffer a negative consequence by using anthropogenic-related material in their nests. These results suggest that despite the potential cost of urban living, finches benefit overall from urban living and urbanization may buffer the effects of limited resource availability in the Galapagos Islands.