Effects of DDE and food stress on reproduction and body condition of ringed turtle doves

Abstract

Six trials with ringed turtle doves (Streptopelia risoria) explored the combined effects of food restrictions and DDE [1,1,-dichloro-2,2-bis(p-chlorophenyl) ethylene] on reproductive performance and body condition. In each trial, eight groups of eight breeding pairs were either exposed (four groups) or not exposed (four groups) to DDE and held on either 100, 90, 80, or 70% of normal food intake. Three performance trials and three condition trials were conducted. In each case, the three trials differed only in the time food was restricted—either 2 weeks before pairing, at pairing, or at egg laying. Performance trials assessed reproductive performance and were continued for about 42 days, the normal period required to fledge young. Condition trials were each terminated at the time most pairs failed in the corresponding performance trial. Pairs were then sacrificed to assess their body condition. In performance trials, treatments severely affected breeding success. Overall, in the three trials, productivity in clean birds was reduced 50, 85, and 100%, respectively, at food intakes of 90, 80, and 70% of normal. Effects were greater on DDE birds; productivity was lowered 23, 87, 98, and 100% at 100, 90, 80, and 70% food intake, respectively. The timing of food restriction was as important as its intensity. A 10% reduction in food before pairing had a greater effect on overall performance than a 30% reduction at egg laying. DDE effects were greatest in birds subjected to food restrictions before egg laying. Treatments affected females more than males. In performance trials, productivity was reduced by nonbreeding and by increased death of embryos and young due to inadequate brooding and care. In condition trials, body condition was not greatly affected by treatments. Losses in body weight and in fat and protein reserves were not as closely related to breeding performance as were reduced size of gonads and crop glands. Treatments apparently restricted breeding success by limiting the levels of hormones necessary to develop and maintain active gonads, adequate courtship and brooding behavior, and functional crop glands. Food is constantly a limiting factor for wildlife. Further reductions in food supplies caused by human activities along with chemical contaminants in the environment can be expected to adversely influence reproductive success and pose serious restrictions on avian populations.