Climate variability influences genetic and phenotypic diversity within species, impacting biodiversity’s evolution. Gene flow and selection maintain changes in genetic and phenotypic variants along an environmental gradient. We investigated a hybrid zone in western Ecuador, involving two wren species (Aves: Troglodytidae), Campylorhynchus zonatus and C. fasciatus, and their admixed populations. We addressed two primary questions: (1) What is the relative contribution of Isolation by Distance (IBD) and Isolation by Environment (IBE) to genetic differentiation in these species along the western Ecuadorian environmental gradient? (2) Is there evidence of genetic admixture and introgression between these taxa in western Ecuador? We analyzed 4,409 SNPs from 112 blood samples sequenced using ddRadSeq. Clusters ranged from K=2-4, aligning with geographic origins, known phylogenetics, and physical or ecological constraints. IBD was evident across all models, while IBE was less pronounced but still significant for annual mean precipitation and precipitation seasonality. Genetic admixture between C. f. pallescens and C. zonatus gradually changed along the environmental gradient. Genetic differentiation in the two C. f. pallescens populations could be attributed to an unreported potential physical barrier in central western Ecuador. The proximity of the Andes to the coastline restricted lowland habitats, limiting dispersal and gene flow, especially among dry-habitat specialists. Taxonomic changes are not proposed, but the admixture in C. f. pallescens suggests it may be a hybrid between C. z. brevirostris and C. fasciatus, with varying degrees of admixture in western Ecuador and northwestern Peru. This study enhances our understanding of avian population genomics in tropical regions.

Documenting patterns of spatio-temporal change in hyper-diverse communities remains a challenge for tropical ecology, yet is increasingly urgent as some long-term studies have shown major declines in bird communities even in relatively undisturbed sites. In 1982, Terborgh et al. quantified the structure and organization of the bird community in a 97-ha. plot in southeastern Peru. We revisited the same plot in 2018 and repeated the same intense combination of methodologies as the original study in order to evaluate community-wide changes. Contrary to the results from studies elsewhere, we found little change in bird distribution and abundance within the plot, although there were some declines related to loss of mixed-species flocks with a high level of species interdependence. This apparent stability suggests that large-scale forest reserves such as Manu National Park may provide the conditions necessary for establishing refugia from at least some of the effects of global change on birds.