Vocal dialects have fascinated biologists for over 50 years. This mosaic pattern of geographic variation in learned vocalizations was first described in a songbird, and since that time, most studies investigating dialects have focused on songbird species. Here we examine patterns of geographic variation in the calls of a different group of vocal learning birds, the parrots (Order Psittaciformes). We summarize the growing literature on vocal variation in parrots, and complement this review with a survey of variation in the genus using calls from sound libraries. We find strikingly similar patterns to those previously found in songbirds. Over 90% of parrots examined in the literature, and 69% of species surveyed, showed geographic variation consistent with a propensity to share local call types. This trait is evolutionarily labile and widespread; within most clades contained species with and without geographic variation, and most major lineages of parrots include representatives with dialects. We found little support for the long-standing hypothesis that dialects isolate populations and thus generate genetic differences among populations. Instead, most studies support the idea that dialects are maintained by social benefits of matching local call types, a finding that has implications for the management of captive and endangered populations. Considerable scope remains for studies that experimentally test hypotheses for the exact nature of these benefits, as well as studies that employ comparisons among species, to understand how the interplay between ecology, social dynamics and vocal learning capacities produces different patterns of variation across the parrots.

Because a population's ability to respond to rapid change is dictated by standing genetic variation, we can better predict a population's long-term viability by estimating and then comparing adult census size () and effective population size ( ). However, most studies only measure or , which can be misleading. Using a combination of field and genomic sequence data, we here estimate and compare and in two range-restricted endemics of the Solomon Islands. Two White-eye species inhabit the small island of Kolombangara, with a high elevation species endemic to the island () and a low elevation species endemic to the Solomon Islands (). Field observations reveal large values of for both species with numbering at 114,781 ± 32,233 adults, and numbering at 64,412 ± 15,324 adults. In contrast, genomic analyses reveal that was much lower than , with estimated at 694.5 and at 796.1 individuals. Further, positive Tajima's D values for both species suggest that they have experienced a demographic contraction, providing a mechanism for low values of . Comparison of and suggests that and are not at immediate threat of extinction but may be at genetic risk. Our results provide important baseline data for long-term monitoring of these island endemics, and argue for measuring both population size estimates to better gauge long-term population viability.