Barrier islands in Louisiana and elsewhere in the northern Gulf of Mexico region provide valuable breeding habitat for numerous waterbird species; however, these islands are also deteriorating at an alarming rate. Management and conservation of waterbird species in these dynamic environments require a better understanding of the breeding biology for northern Gulf of Mexico populations. Productivity parameters were investigated for Royal (Thalasseus maximus) and Sandwich (T. sandvicensis) terns at the Isles Dernieres Barrier Island Refuge in Terrebonne Parish, Louisiana, during the 2009 and 2010 breeding seasons. Mean hatching success for Royal Tern was 77% (n = 169 nests), while Sandwich Tern hatching success was 75% (n = 130 nests). For both Royal and Sandwich terns, the estimated probability that a chick survived from hatching to fledging age was 55% (n = 630 nestlings). Overall, estimated breeding success for Royal and Sandwich terns was 42.3% and 41%, respectively. Chick growth rates were similar for both species and among islands, suggesting similar habitat quality among islands of Isles Dernieres Barrier Island Refuge. Growth rates (K) for both Royal and Sandwich terns were greatest for tarsus (K = 0.194 and K = 0.184, respectively), followed by mass (K = 0.143 and K = 0.164, respectively), and then wing cord (K = 0.125 and K = 0.110, respectively). Future studies evaluating causes of chick mortality would provide insight into the quality of habitat provided during this life stage. Chick growth rates may also be a useful indicator of ecological change and response to disturbances such as the Deepwater Horizon oil spill.
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Vol. 37 • No. 3