Least tern chick survival on the Lower Mississippi River

Accurate population models for the endangered Interior Least Tern (Sterna a ntillarum) cannot be generated without;age-specific survival estimates. Our purpose was to estimate chick survival from hatching to fledging, for Leas t Terns nesting at two sites on the Lower Mississippi River in Missouri, us ing mark-recapture methodology. We banded 110 Least Tern chicks during 1995 on sand island nesting colonies situated at river kilometers (Rkm) 1431 an d 1481 on the Lower Mississippi River. We used Program JOLLY to compute sur vival point estimates, their associated variances, and goodness-of-fit test s for Jolly-Seber open population models (Pollock et al. 1990). The mean da ily survival rate for Least Tern chicks at Rkm 1431 was 0.951 (SE = 0.03) w ith 95% confidence intervals of 0.899-1.003. Mean daily survival rate for L east Tern chicks at Rkm 1481 was 0.972 (SE = 0.03) with 95% confidence inte rvals of 0.911-1.034. Estimated survival of Least Tern chicks throughout th e 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 chick s we estimated 0.72 and 1.0 fledglings/pair were produced at Rkm 1431 and R km 1481, respectively.