Nest Success and Chick Survival of Black Terns in Maine: Effects of Predation on Breeding Productivity

Nest predation is a prominent cause of reproductive failure in wetland-nesting birds, including black terns. As a result, predator avoidance should play an important role in nest site selection. I examined intraspecific variation in nest success to identify factors affecting nest predation of black tern colonies in central Maine. I measured variables related to proximity of wetland features and nest aggregation for 231 successful and 124 depredated black tern nests during the period 1998-2002. I defined candidate models based on logistic regression and selected models with Akaike\u27s Information Criterion adjusted for small sample sizes (AICc) to determine the best model for predicting nest outcome (success vs. depredated). Variables related to proximity to depredated nests, including the number of depredated nests within 30 meters and the number of depredated nests between 30-100 meters, were the most important factors influencing nest predation of black terns in Maine colonies during 1998-2002. Losses to predation were localized, suggesting nest predators in Maine wetlands exhibit area-restricted search behavior. Factors related to colonial nest defense, nest concealment, and iii proximity to wetland features were found to have little effect on the likelihood of nest predation. Nocturnal nest absence in Laridae has been correlated with increased nest predation, prolonged incubation periods, and lowered chick survival. I monitored 45 nests in 2001-2002 with temperature monitors to determine the occurrence and duration of nocturnal nest absence in black terns and the effect of absence on nest temperature and incubation length in Maine colonies. Nocturnal absences occurred at 33 of 45 black tern nests, suggesting this behavior is common. In 2001, 36 absences lasting 60 minutes or longer were recorded, whereas only nine absences exceeded 60 minutes in 2002. Nocturnal absences among adjacent nests were rarely synchronous. The mean temperature decrease for absences greater than or equal to sixty minutes was 9.62 ºC. Nest absence did not appear to influence nest predation rates or incubation length, but the indirect effects of absence on breeding productivity of black terns merits future research. Chick survival is an important parameter of black tern population growth, but few studies have identified factors contributing to chick mortality. I utilized predator exclosures to determine whether predation and/or food resources were limiting chick survival of black terns in Maine colonies in 2001-2002. I assumed if predation were limiting, chick survival should be 100% in broods excluded from predation. Nests were also monitored in unenclosed clusters of nests to confirm that chick survival was as low as previous years. I also measured chick growth by hatch-order during the period from hatch to near-fledgling as an indicator of potential food limitation. Chick survival in the absence of predation was 88.2% in 2001 and 88.9% in 2002. Survival of chicks at unenclosed nests was 10.4% in 2001 and between 39.4-61.3% in 2002. I did not see iv evidence of differential chick growth with hatch-order, suggesting food limitations were not present in 2001-2002. My results suggest predation is the primary factor limiting chick survival in Maine colonies. Additionally, I describe the design of predator exclosures utilized in this study and report on their efficacy at excluding predators