Journal Article

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

Chernicky, Kiley, Harvey, Johanna A., Chaves, Jaime A., Simons, Shelby R., Knutie, Sarah A., Verrett, Taylor B.

2021

Overview

Urbanization is expanding worldwide with major consequences for organisms. Anthropogenic factors can reduce the fitness of animals but may have benefits, such as consistent human food availability. Understanding anthropogenic trade‐offs is critical in environments with variable levels of natural food availability, such as the Galápagos Islands, an area of rapid urbanization. For example, during dry years, the reproductive success of bird species, such as Darwin's finches, is low because reduced precipitation impacts food availability. Urban areas 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, such as the incorporation of anthropogenic debris (e.g., string, plastic) into their nests, which may increase mortality. In our study, we determined the effect of urbanization on the nesting success of small ground finches (Geospiza fuliginosa; a species of Darwin's finch) during a dry year on San Cristóbal Island. We quantified nest building, egg laying and hatching, and fledging in an urban and nonurban area and characterized the anthropogenic debris in nests. We also documented mortalities including nest trash‐related deaths and whether anthropogenic materials directly led to entanglement‐ or ingestion‐related nest mortalities. Overall, urban finches built more nests, laid more eggs, and produced more fledglings than nonurban finches. However, every nest in the urban area contained anthropogenic material, which resulted in 18% nestling mortality while nonurban nests had no anthropogenic debris. Our study showed that urban living has trade‐offs: urban birds have overall higher nesting success during a dry year than nonurban birds, but urban birds can suffer mortality from anthropogenic‐related nest‐materials. These results suggest that despite potential costs, finches benefit overall from urban living and urbanization may buffer the effects of limited resource availability in the Galápagos Islands. Urbanization is expanding worldwide with major consequences for organisms, understanding the trade‐offs of urbanization is of critical importance, particularly in environments with unreliable annual natural food availability, such as the Galápagos Islands. Our study examined the effect of a dry year on the reproductive effort and success of Darwin's finches. We found that urban birds have overall higher reproductive success than nonurban birds, but urban birds can suffer a negative consequence by using anthropogenic‐related nest‐materials, suggesting that despite the potential cost of urban living, finches benefit overall from urban living and urbanization may buffer the effects of limited resource years. Photo credit: Kiyoko Gotanda

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc,Wiley
• Subject: Animal behavior / Animal reproduction / anthropogenic debris / Anthropogenic factors / Availability / Biodiversity / Breeding success / Debris / Detritus / dry year / Egg laying / Eggs / El Nino / Entanglement / Food / Food availability / Galápagos Islands / Geospiza fuliginosa / Hatching / Human influences / Ingestion / Islands / La Nińa / Mortality / Native species / Natural & organic foods / Nest building / nest material / Nesting / Nests / Original Research / Population / Reproduction / Reproductive fitness / Resource availability / Seasons / Songbirds / Success / trash / Urban areas / urban ecology / Urbanization