Management implications of population genetics and demographics of least terns (Sterna antillarum)

Scope and method of study. The purpose of this study was to assess factors influencing survival and subspecies validity of Least Terns (Sterna antillarum). The study was conducted at three scales: national, regional, and local. At the national scale, I assessed the level of genetic variation among California (S. a. browni), Interior (S. a. athallasos), and Eastern (S. a. antillarum ) populations that have been designated as subspecies by the American Ornithologists' Union (a professional society that publishes a complete list of avian species in North America). At the regional level, the probability of population persistence was evaluated for three breeding populations of Interior Least Terns based on a minimum of 7 years of data collected from the population in question. I also examined the sensitivity of population growth to changes in demographic parameters. At the local level, impacts of tourism activities on a breeding population of Least Terns were assessed at Salt Plains National Wildlife Refuge (SPNWR), Alfalfa County, Oklahoma.; Findings and conclusions. Based on nuclear and mitochondrial (mtDNA) analyses California, Interior, and Eastern breeding populations of Least Terns do not qualify as subspecies. Gene flow was substantially higher for mtDNA than nuclear DNA. This may indicate female dispersal with male philopatry. Of three breeding populations of Interior Least Tern, only one appears to be self-sustaining. Population viability was most sensitive to changes in adult survival. Breeding populations appear to be able to increase numbers when adult survival is high. Unfortunately, the migratory nature of least terns limits the effectiveness of conservation efforts directed at adult survival. At a local level, the tourism activities at SPNWR did not adversely impact reproduction of breeding colonies despite occurring within the center of nesting habitat. This was attributed to the early initiation of tourism activities prior to arrival of nesting birds. If population numbers and breeding habitat increase, it does not appear that least terns possess regional differences that might reduce survival of dispersing individuals.