Biological dimensions of tern management-a case study of the least tern in Sonora, Mexico, and a comparative analysis of reproductive investment in terns

Least terns (Sternula antillarum) are threatened by rapid human development on the northern coast of Sonora, Mexico. Terns are bellwethers for changes along the world's coastlines, as their coastal breeding habitat is vulnerable to flooding and development. We conducted targeted ground and aerial surveys for least tern colonies along 160 kilometers of coast, and document our findings on colony sizes at nine sites over 3 years in the first portion of this report.

Like many taxa, terns lay larger clutches at higher latitudes. In the second portion of this report, we evaluate least tern breeding lifespan, food availability, and nest predation as potential ecological reasons behind this differing clutch-size pattern. After correcting for phylogenetic relationships, we found that food availability, not breeding lifespan or nest predation rate, was related to reproductive investment across 46 species and populations of terns. We conclude that coastal development may have a greater impact on nesting terns in tropical regions as compared to temperate breeding locations, because global oceanic patterns of decreased food availability reduce reproductive investment in the tropics.