Birds--Reproduction

Avian reproduction is generally resource dependent, and resource availability can vary through time and space. Wading birds breeding activity in southern Florida wetlands is limited by availability of aquatic prey, which is largely influenced by seasonal hydrodynamics. Restoration of natural hydrologic patterns is expected to increase populations and return breeding activity in the southern Everglades, but which prey support successful breeding at coastal colonies is unknown. To address this, I examined prey use of nesting White Ibis (Eudocimus albus) at coastal colonies in Everglades National Park (ENP) in a two-year observational study. I also examined ibis diets at nesting colonies located in three regions of the Everglades to better understand regional variation in trophic support of ibis reproduction. I found that crayfish and fish were used extensively in ENP in a year with exceptional ibis breeding activity, and I provide evidence that lengthened hydroperiods in higher elevation marl prairies may enhance crayfish production and availability in the southern Everglades. I found that crayfish were the most important prey type in all regions of the Everglades when reproductive effort was highest. These results add to the growing body of evidence that crayfish are important prey for ibis reproductive success in all parts of the Everglades, and suggest that increasing water flowing into the southern Everglades may incite greater nesting at historic colony locations. With this knowledge we can forecast how wading birds, and more generally wetlands of southern Florida, will respond to a changing environment and potential restoration scenarios.

Depo-Provera, a drug manufactured by the Upjohn Company, has been used clinically to prevent egg-laying in several species of domestic birds. Two different doses of the drug plus a placebo injection of saline were administered to 54 cockatiels. All subjects appeared normal and healthy throughout the study except for two birds in the higher dose treatment which died of unknown causes. Control was studied through the direct observation of the ovary by means of laparoscopy, as well as monitoring egg laying activity throughout the study. Depo-Provera at both doses tested appears to effectively decrease egg-laying activity in the captive cockatiel. All birds receiving the higher dose of Depo-Provera gained significant weight. Although the use of Depo-Provera may serve as a means of preventive medicine, there are serious side effects that should be considered.

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.