Study system
The study was conducted between February – May 2018 and 2019 (during the breeding season) in the arid lowlands of San Cristóbal (557 km2) in the Galápagos Islands. The urban area was in the capital city of Puerto Baquerizo Moreno (0°54’9”S, 89°36’33”W) (hereon, urban area), which is the only large town on San Cristóbal and the second largest city in the Galápagos archipelago with a human population of 7,199 (INEC, 2016). The urban area primarily consists of impermeable concrete or stone surfaces and human built structures in altered landscapes. Our urban study area measured 0.79 km2 (~1.2 km by 0.62 km) and included tourist and residential zones. The non-urban area was in Jardín de Opuntias (0°56’18.92”S, 89°32’54.93”W) (hereon, non-urban area), which is a Galápagos National Park site located 4.5 km southeast of the urban area. This site consisted of vegetated natural habitats with no unnatural impermeable surfaces present. Our non-urban study area measured 0.21 km2 and covered 1.4 km of the main trail and 0.15 km to each side.
Small ground finches are abundant at both field sites (Harvey et al., 2021). Small ground finches build domed-shaped nests in native and non-native trees and shrubs as well as human-built structures, depending on the location. On San Cristóbal Island, they lay 1-4 eggs per clutch (mean = 2.84 eggs) and have an average of 2.83 nestlings per brood across urban and non-urban areas. However, in some years, nests in urban areas contained more eggs than non-urban areas, yielding higher nestling survival (Harvey et al., 2021).