Birds--Infancy

Least Terns (Sterna antillarum) have recently shifted from traditional beach nesting sites to flat gravel roofs in parts of their range. In an attempt to determine whether the thermal environment of novel roof sites contributes to nesting success relative to that of traditional sites, hatching and fledging success and fifteen possible thermoregulatory behaviors of roof-nesting Least Terns were examined at four sites in Palm Beach County, Florida in 1992. The mean numbers of chicks and fledglings produced/nest (1.13 and 0.70, respectively) were significantly higher than those reported in other recent studies, indicating that nesting on some roofs is successful and may be a good alternative to beach locations. There was no difference between equivalent temperatures at the roofs and at a nearby beach, thereby suggesting that the new thermal environments of roofs do not adversely influence hatching and fledging success in Least Terns.

Few studies have addressed reproductive success and nestling growth of the Caribbean population of Roseate Terns (Sterna dougallii), and no one has studied the most northerly nesting colonies in Florida. Two colonies in Florida, a ground colony (Pelican Shoal), and a roof colony (Marathon Government Center) were examined in 2000 and 2001. This study found the roof and ground colony to have similar incubation periods, days to fledging, linear growth rates, and asymptotic mass. However, clutch size, hatch success, and annual reproductive success were more variable between the colonies and between the two years. Most of this variability resulted from high nest and chick loss at Pelican Shoal due to avian predators, nesting sea turtles, and strong summer storms. Artificial habitat (nest boxes and tires), placed at the two colonies to improve reproductive success, was not utilized by Roseate Terns for nesting but was used by nesting Bridled Terns (Sterna anaethetus ) at Pelican Shoal. Air temperatures were higher at the roof colony than the ground colony and higher in the artificial habitat than in "natural" nesting substrates.