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

Abstract

O_LIUrbanization is expanding worldwide and can have major consequences for organisms, anthropogenic factors can reduce the fitness of animals but may also have benefits, such as consistent human food availability. Understanding these trade-offs is critically important in environments with unreliable annual natural food availability, such as the Galapagos Islands where urbanization is rapidly increasing. For example, during dry climatic condition years, the reproductive success of bird species, such as Darwins finches, is low because low precipitation reduces food availability. Urban areas in the Galapagos provide supplemental human food to finches, which could improve their reproductive success during years with low natural food availability. However, urban finches might face trade-offs, as the incorporation of anthropogenic debris (e.g. string, hair, plastic) into their nests can increase mortality. C_LIO_LIIn our study, we determined the effect of urbanization on the reproductive effort and success of small ground finches (Geospiza fuliginosa; a species of Darwins finch) during a dry year on San Cristobal Island, Galapagos Islands. We also documented the abundance of anthropogenic debris incorporated in to nests. C_LIO_LIWe quantified nest building, egg laying, hatching, and fledging of small ground finches in an urban and non-urban area. We also qualified the type of anthropogenic debris in finch nests and the quantified the percent of debris comprising total nest mass. We determined whether incorporating these materials into the nest directly led to entanglement- or ingestion-related mortalities. C_LIO_LIOverall, urban finches built more nests, laid more eggs, and produced more fledglings than non-urban finches. However, every nest in the urban area contained anthropogenic-related material, which resulted in entanglement- or ingestion-related mortalities in 18% of nests with nestlings. Non-urban nests did not contain any anthropogenic-related material. C_LIO_LIOur study showed that urban living has trade-offs during drier climatic conditions: 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 for nesting. 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. C_LI