Body Condition and Response to Pesticides in Woodcocks

Abstract

Response of woodcocks (Philohela minor) to heptachlor dosage was closely related to the physical condition of the birds, as reflected by body weight and by body weight in relation to capture weight: in a series of tests with underweight birds, nearly all woodcocks died at dosage levels well below those at which nearly all the birds in a normal-weight series lived. Heptachlor residues in tissues were determined and their loss with time was estimated. Dieldrin proved more toxic than heptachlor to birds of similar weight. Birds in good weight survived massive doses of DDT; some succumbed to smaller spaced serial doses, but only when these were accompanied by starvation rations. When birds were placed in foil-lined boxes after doses of heptachlor added to butter oil or corn oil, it became evident that they passed quantities of oil in about 3 hours, thus very likely ridding themselves of a large part of the heptachlor dose. It was concluded that other methods than dosage with encapsulated chemicals would be needed for appraisal of field effects of toxicants on woodcocks. Investigations of the effects of heptachlor on woodcocks were begun in 1959 because of the potential hazard of this chemical on the southern wintering grounds, which are within the area treated extensively for control of the imported fire ant (Solenopsis saevissima). As a first step, exploratory tests of acute toxicity of heptachlor were made at the Massachusetts Cooperative Wildlife Research Unit at Amherst. DDT and dieldrin dosages were tried also, because they, too, are chemicals to which woodcocks may be exposed in many areas. Additional tests with heptachlor were made at the Patuxent Wildlife Research Center, Maryland, in 1960. The purposes of this paper are (1) to show the relationship between weight, time in captivity, and effect of toxicant; (2) to demonstrate the resistance of woodcocks to large doses of encapsulated toxicant; (3) to record residue content of dosed birds and to approximate the loss rate of heptachlor residues; and (4) to record mortality data-these are given in some detail, for, although they are not in standard LD50 form, they provide the only available data for a species that offers unusually difficult problems in xperimentation. For the studies of both years, woodcocks were caught in mist nets near Amherst. Housing and care of the birds were as described by Stickel, Sheldon, and Stickel (1965). Assistance was received from several people in various parts of the work. John L. Buckley facilitated and encouraged the tests in 1960 and the analyses that followed; Don W. Hayne helped plan the 1960 tests and provided critical analysis of data from the entire study. Allyn Coombs helped perform the experiments at Amherst in 1959. Residue analyses were made at the Patuxent Wildlife Research Center by Vyto Adomaitis, Calvin Menzie, and William Reichel. EXPERIMENTS WITH HEPTACHLOR Tests in 1959 explored the lethal levels of capsule dosages of heptachlor to captive woodcocks. With this rangefinding as background, tests in 1960 were planned to refine the 1959 determinations, using a stepwise procedure recommended by Hayne for obtaining an LD50 determination with the most economical use of birds. When it was