Least tern chick survival on the Lower Mississippi River

Accurate population models for the endangered Interior Least Tern (Sterna antillarum) cannot be generated without;age-specific survival estimates. Our purpose was to estimate chick survival from hatching to fledging, for Least Terns nesting at two sites on the Lower Mississippi River in Missouri, using mark-recapture methodology. We banded 110 Least Tern chicks during 1995 on sand island nesting colonies situated at river kilometers (Rkm) 1431 and 1481 on the Lower Mississippi River. We used Program JOLLY to compute survival point estimates, their associated variances, and goodness-of-fit tests for Jolly-Seber open population models (Pollock et al. 1990). The mean daily survival rate for Least Tern chicks at Rkm 1431 was 0.951 (SE = 0.03) with 95% confidence intervals of 0.899-1.003. Mean daily survival rate for Least Tern chicks at Rkm 1481 was 0.972 (SE = 0.03) with 95% confidence intervals of 0.911-1.034. Estimated survival of Least Tern chicks throughout the entire 17-d fledging interval was 0.43 at Rkm 1431 and 0.62 at Rkm 1481. Based oil survival rate estimates and number of known pairs producing chicks we estimated 0.72 and 1.0 fledglings/pair were produced at Rkm 1431 and Rkm 1481, respectively.