The Foraging and Habitat Ecology of Black Terns in Maine

The population of Black Terns in Maine is small and factors related to the ecology of this species’ foraging and habitat ecology might limit population growth and recovery. The objectives were to (1) determine if diet and provisioning rates are limiting chick growth, (2) identify and rank suitable habitat in Maine, and (3) determine if precipitation patterns and water level dynamics are limiting in Maine. I compared growth rates of chicks in 1998-2000 in Maine to rates from other studies, determined the influence of colony, year, and diet on growth rates and food deliveries and used an energetics model to determine the sensitivity of growth rates to feeding parameters. To identify potential wetland habitat, I used a Geographic Information System analysis of National Wetlands Inventory data from Maine based on the following criteria: wetland complexes were \u3e5 ha total area with \u3e1 ha open water and contained semi-permanently flooded emergent wetland. To assess effects of flooding, I determined the probability of occurrence for 3 levels (low, moderate, and catastrophic)?of nest losses associated with flooding, based on nest loss data and stream gauge and precipitation data for 1960-1999. Growth rates of Black Tern chicks in Maine ( ? = 4.46 g/d) were similar to other studies (range 4.18-5.18 g/d) and varied with hatch order and brood, but not year or colony. Third-hatched chicks (of 3) grew most slowly ( ? = 4.15 g/d) but at greater rates than one reported estimate (3.32 g/d) for starved chicks. Patterns of food deliveries were complex. The ratio of fish to insects in the diet ranged from 3.4-13.3, and total delivery rates varied widely (9.1-23.7 items/brood-hr), but there was no evidence that growth rates differed among diets. Weight change in chicks was best predicted by delivery rates of large fish, large and small insects, and temperature; however, modeling indicated that growth rates were most sensitive to rates of large insect delivery. My results indicate that diet type did not influence growth rates of chicks at the observed rates of delivery, and overall there was no evidence that food resources limited fledging rates in Black Terns in Maine. I identified 730 potential colony sites for Black Terns in Maine. Potential sites ranged in size from 5-30,864 ha ( ? = 425 ha) and had 0.04-228 ha of semipermanently flooded emergent wetland. However, only 51 sites were classified as high potential sites (\u3e20 ha of semi-permanently flooded emergent wetland) The availability of potential sites does not appear to be limiting the population of Black Terns in Maine, but these sites should be ground surveyed because wetland classification data may be out-dated or too coarse-grained. Moderate flooding events have the potential to cause the greatest long-term effect on nesting success in Maine because of a high frequency of occurrence (38% of years)?and \u3e50% nest loss in the largest colony and 36% in other colonies. Small flooding events occurred often (70% of years), but resulted in few nest losses and catastrophic flooding events caused extensive nest losses (\u3e94% in the largest colony and 36% in other colonies) but occurred in only 13% of years