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).