Survival and Movement of Chicks of the Least Tern (Sterna antillarum) on an Alkaline Flat

Abstract

Survival of chicks of the interior least tern (Sterna antillarum athalassos) has been difficult to estimate due to their semi-precocial development and cryptic coloration. After chicks disperse from the nest, they rarely are relocated. Our objectives were to estimate survival of chicks and study their movement patterns. In 1999, we attached radiotransmitters to 25 chicks and tracked them for 2–19 days depending on retention of transmitter. Because fate could not be determined always when signals were lost, a high and low estimate of survival was calculated. Kaplan-Meier estimates of survival were calculated first by assuming that all lost signals represented mortalities, and second that these transmitters failed and chicks were alive. This resulted in a minimum estimate of 5% of chicks surviving at the end of the study period and a high of 27%. Five chicks fledged, six died, and fate of the remaining 14 was undetermined. Although chicks appeared to allocate a substantial part of their daily movement to nocturnal periods, average rates of diurnal (7.6 m/h) and nocturnal movement (12.5 m/h) did not differ. Chicks primarily moved toward stable sources of water.