Use of social information for habitat selection in songbirds

Background/Question/Methods

Habitat selection research has primarily focused on associations between species distributions and vegetative and geologic habitat characteristics or, where behavioral interactions have been considered, on antagonistic interactions and negative density dependence. However, conspecific location cues can influence habitat selection by providing information about habitat quality and inducing attraction and formation of conspecific aggregations that can confer fitness benefits. I conducted replicated, manipulative experiments on 27 pairs of sample units in 2008 to 2010 on private lands in east-central Texas to investigate use and relative influence of conspecific location cues in habitat selection for the federally endangered golden-cheeked warbler (Dendroica chrysoparia). I investigated response to conspecific cues in oak juniper (Quercus spp.-Juniperus asheii) woodland over a range canopy cover considered poor to optimal habitat, and compared response to cues presented during the pre-settlement and the post-breeding time period. Treatment was comprised of broadcast golden-cheeked warbler vocalizations during the pre-settlement or post-breeding periods. I conducted territory mapping and behavioral surveys >1 per week to estimate territory density, pairing success, and fledging success. 

Results/Conclusions

Density of warbler territories was >2 times higher in treatment units than controls for all experiments across the range of canopy cover (P = 0.02), suggesting conspecific cues may trump the influence of canopy cover in habitat selection decision-making. Pairing and fledging success was not related to canopy cover; birds induced to select areas typically considered unsuitable did not experience poorer fitness outcomes than birds selecting higher canopy cover sites. Pairing success was positively correlated with territory density (ρ = 0.506, P = 0.008), suggesting males experienced positive fitness benefits of aggregating with conspecifics. Territory density was higher in response to pre-settlement conspecific vocalization treatment than for post-breeding treatment (W=100, P = 0.004). Results suggest that both pre-settlement and post-breeding conspecific locations cues can strongly influence warbler habitat selection, induce settlement in areas that might otherwise not be selected, and produce differential territory densities or aggregations within areas of similar vegetative characteristics. Identifying how organisms use social information to make habitat selection decisions is essential for improving our understanding of species distributions, habitat use, and fitness consequences of habitat selection decisions; our ability to predict impacts of changes in habitat; the accuracy of spatially-explicit predictive species distribution models; and the efficiency and efficacy of our tools and approaches to conservation and management.