Exploration behavior differs between Darwin’s finch species and predicts territory defense and hatching success

Darwin’s finch species in the Galápagos Islands are famously distinguished by their morphology but less attention has been given to behavioral differences between species. In this study, we compared behavior between four Darwin’s finch species on Floreana Island: small ground finch (Geospiza fuliginosa), medium ground finch (G. fortis), small tree finch (Camarhynchus parvulus), and medium tree finch (C. pauper). After capturing birds using mist-nets, we measured three behavioral traits: (1) boldness during human handling, (2) exploration in a novel environment, and (3) aggressiveness towards their mirror image. First, we found that ground finches were bolder and more exploratory than tree finches, consistent with their distinct ecological niches on Floreana Island and with the theoretical prediction that diet generalists should be less wary of novelty. Second, we tested the ecological validity of these behavioral variables at the individual level by relating them to territory defense behavior and breeding success. We found that males that were more exploratory in the novel environment also reacted more aggressively to a simulated territory intruder and showed lower offspring hatching success during the breeding season. Hence, our findings support previous work showing behavioral differences between Darwin’s finch species and also suggest pathways by which behavioral differences among individuals might influence fitness. Significance statementClosely-related species that overlap in their geographical range may differ in their morphology and/or behavior, allowing them to occupy different ecological niches. In this study, we explored behavioral differences between four Darwin’s finch species on Floreana Island in the Galápagos Archipelago. We found clear interspecies differences in behavior, with the ground finches struggling more often during handling (boldness) and visiting more sectors in a novel environment (exploration) compared to the tree finches. After birds were released, we continued to observe a subset of male finches in the wild. An individual’s exploration behavior significantly predicted both its aggressive response to a territory intruder (simulated using song playback) and offspring hatching success during the breeding season. This suggests that individual differences in exploration behavior can potentially be used as a proxy for territorial behavior in the wild and may also predict fitness outcomes.</p

Age effects in Darwin’s finches: older males build more concealed nests in areas with more heterospecific singing neighbors

Nesting success tends to increase with age in birds, in part because older birds select more concealed nest sites based on experience and/or an assessment of prevailing predation risk. In general, greater plant diversity is associated with more biodiversity and more vegetation cover. Here, we ask if older Darwin’s finch males nest in areas with greater vegetation cover and if these nest sites also have greater avian species diversity assessed using song. We compared patterns in Darwin’s Small Tree Finch (Camarhynchus parvulus) and Darwin’s Small Ground Finch (Geospiza fuliginosa) as males build the nest in both systems. We measured vegetation cover, nesting height, and con- vs. heterospecific songs per minute at 55 nests (22 C. parvulus, 33 G. fuliginosa). As expected, in both species, older males built nests in areas with more vegetation cover and these nests had less predation. A novel finding is that nests of older males also had more heterospecific singing neighbors. Future research could test whether older males outcompete younger males for access to preferred nest sites that are more concealed and sustain a greater local biodiversity. The findings also raise questions about the ontogenetic and fitness consequences of different acoustical experiences for developing nestlings inside the nest.</p