Osprey (Pandion haliaetus) eggs were exchanged between Connecticut and Maryland osprey nests in 1968 and 1969 to test the hypothesis that the decline in reproductive success of Connecticut ospreys was caused by something within the external environment of the eggs. Incubation of 30 Connecticut osprey eggs by Maryland ospreys did not improve the hatching rate. Forty-five Maryland osprey eggs incubated by Connecticut ospreys hatched at their normal rate. The results of the egg exchanges and associated observations indicated that the most probable cause of the poor reproduction of Connecticut ospreys was related to contamination of the birds and their eggs. Residues of DDT and its metabolites, dieldrin, and PCBs were generally higher in fish from Connecticut than from Maryland. During 1968-69, average residues (on a nest basis) in osprey eggs from Maryland were: p,p'-DDE, 2.4 ppm; dieldrin, 0.25 ppm; PCB, 2.6 ppm. Average residues in eggs from Connecticut for the same period were: p,p'DDE, 8.9 ppm; dieldrin, 0.61 ppm; PCB, 15 ppm. There were no major changes in residue content of Connecticut eggs collected in 1964 compared with those collected in 1968-69. One Connecticut osprey had a concentration of dieldrin in its brain which was in the lethal range. The average shell thickness of recently collected osprey eggs from Connecticut had declined 18 percent, and those from Maryland had declined 10 percent from pre-1947 norms. Dieldrin, DDE, and PCB are three environmental pollutants that have most likely been important factors in the greatly reduced reproductive success and rapid population decline of Connecticut ospreys. J. WILDL. MANAGE. 39(1):124-139 Ospreys traditionally nested in large numbers along the coasts of New York and Connecticut around Long Island Sound (Bent 1937) and of Chesapeake Bay (Tyrrell 1936). In the late 1960's the osprey population on Chesapeake Bay appeared to be relatively stable (Stickel et al. 1965, Reese 1970); production of young averaged about one per active nest. In contrast, the population on Long Island Sound, particularly near the mouth of the Connecticut River, had undergone a severe decline in number of breeding pairs during the late 1950's and early 1960's (Ames and Mersereau 1964, Ames 1966). Poor production of young was the primary cause of the population decline (Ames and Mersereau 1964). A high percentage of eggs failed to hatch, some of which disappeared during the incubation period for reasons unknown, and others were incubated far longer than normal. Mammalian predation, a possible cause of egg disappearance, was effectively eliminated at most nests. Human disturbance was thought to have minimal effects on osprey reproduction. Survival of nestlings appeared normal. Production of fledglings for the years 1960-63 averaged only 0.23 per active nest (36 young in 157 nestings) (Ames and Mersereau 1964), which is far below that found by Reese (1970) on Chesapeake Bay, and also well below the rate required to maintain a stable population (Henny and Wight 1969). Others have reported severe declines in osprey populations on areas adjacent to Long Island Sound (Emerson and Davenport 1963, Peterson 1969). As a result of these findings regarding 1 Present address: Section of Ecology and Systematics, Cornell University, Ithaca, New York 14850. 2 Present address: Charles M. Russell National Wildlife Range, Lewiston, Montana 59457. 124 J. Wildl. Manage. 39(1):1975 This content downloaded from 40.77.167.85 on Mon, 11 Jul 2016 05:35:58 UTC All use subject to http://about.jstor.org/terms EFFECTS OF POLLUTANTS ON OSPREYS ? Wiemeyer et al. 125 reproduction of ospreys in the Northeast, we initiated a study involving both Maryland and Connecticut ospreys. By comparing differences in hatching rates of eggs within, and those moved between, the two areas, we hoped to determine whether the recurrent nesting failure of Connecticut ospreys was caused by one or more of the following types of factors: (1) external environmental effects such as human disturbance, predation, and/or an inadequate food supply, (2) abnormal adult behavior, especially during incubation, and (3) adverse effects of environmental pollutants within the birds and/or their eggs. This paper documents the results of the egg exchange and provides additional information relevant to the declines in the population and reproductive success of Connecticut ospreys. We wish to thank B. B. Collette, formerly with the U.S. Bureau of Commercial Fisheries, for identification of the fish samples. L. N. Locke autopsied the birds and provided the data regarding his findings. R. S. Christensen of WARF Institute, Inc., Madison, Wisconsin, kindly provided the method used in the mercury analyses. R. G. Heath provided advice regarding the statistical analyses. The Division of Management and Enforcement of the U.S. Bureau of Sport Fisheries and Wildlife provided a pilot and aircraft used in transferring the eggs in 1969. J. R. Maestrelli assisted with field work on the Maryland study area. T. E. Lovejoy made available to us the adult ospreys and several eggs that he collected in 1967. E. H. Dustman reviewed a draft of the manuscript and provided helpful suggestions. MATERIALS AND METHODS An experiment was initiated in 1968 in which eggs from nests in Connecticut estuarine areas (Fig. 1) were exchanged CONN. N 5