Geographic distribution of genetic variation in ten species of North American forest birds: island endemism and transcontinental ranges

Abstract

Comparative genetic studies of geographically co-occurring species can lend insight into current and historic relationships among populations and species. This enables examination of similarities and differences among species and provides information about historic processes leading to current genetic and geographic distributions. I used this approach to study two different types of avian co-distribution: island endemism and transcontinental ranges. The Queen Charlotte Islands (QCI), Canada, have many endemic subspecies; historically it may have been a glacial refugium. I used genetic analyses to determine subspecies uniqueness and to identify units of conservation for five species, four with endemic QCI subspecies. I found that QCI populations were genetically differentiated from mainland populations, although each species had a different isolation history, and that QCI is an important area for avian conservation and management. East-to-west genetic splits across North America are seen in vertebrates and may be the result of Pleistocene glacial cycles. Five migratory thrushes successfully colonized northern North America. They have overlapping transcontinental ranges and similar ecological niches in woodland communities. I used genetics to determine how these thrushes established continent-wide ranges. Despite their ecological and distributional similarities these five thrush species had different patterns of colonization across North America.