Annual survival of red knots (Calidris Canutus Rufa) wintering in Florida

Abstract

Populations of Red Knots (Calidris canutus rufa) have declined an estimated 80% in the past 25 years. Declines are primarily attributed to dwindling food resources in Delaware Bay, their last migratory stopover before the breeding grounds. Red Knots wintering in Florida also decreased in numbers, prompting the need to estimate local vital rates to determine whether local factors contribute to declining trends. We estimated age-specific annual survival rates and compared them with estimates from populations of Red Knots wintering in South America using the Barker model. Adult annual survival rates between 2005and 2010 averaged 0.89± 0.02 [SD]; range: 0.86-0.94) and were similar to estimates reported for Delaware Bay (0.87-0.92). Juvenile survival (0.95 ± 0.06[SE]) and adult fidelity (0.81 ± 0.05 [SE]) were also high. However, juvenile survival did not include the period between fledging and arrival in Florida, a period of potentially high mortality. Similar adult survival rates suggested that there was no apparent survival cost for adults migrating to and from Florida compared with those migrating elsewhere. Factors that influence adult survival likely affect populations of C. c. rufa where they co-occur (e.g., breeding grounds, staging areas). Low year- To-year variation (CV = 2.24%) of adult survival suggests that other vital rates with higher variation (e.g., recruitment) may exert a stronger influence on population growth and partly account for the observed decline. Status projections require estimates of fecundity, year-round juvenile survival, and winter distribution in the United States.