DDE Residues and Eggshell Thickness in Prairie Falcons

Abstract

The eggshell thickness of prairie falcon (Falco mexicanus) eggs collected in Colorado in 1967-68, and 1972, is related linearily and inversely to the logarithms of the DDE content of the eggs. This relationship is not statistically different from that found in peregrine falcons (F. peregrinus) and brown pelicans (Pelecanus occidentalis). DDE levels in prairie falcon eggs are about one-fifth and onesixteenth those shown in Alaskan peregrine eggs and California brown pelican eggs, respectively, and despite some shell thinning, prairie falcons in Colorado are reproducing well. Shell thickness averaged higher, egg DDE residues lower, and hatch rate was greater in 1972 than in 1967-68 in the prairie falcons, but the differences are not significant. J. WILDL. MANAGE. 37(4):476-478 Several species of raptorial and fish-eating birds have been shown to lay eggs with shells thinned in relation to the amount of DDE residues in the egg contents (Hickey and Anderson 1968; Fyfe et al. 1969); shell thinning has been experimentally produced in kestrels (F. sparverius) fed DDT and dieldrin (Porter and Wiemeyer 1969), or DDE (Wiemeyer and Porter 1970), and in mallards (Anas platyrhynchos) fed DDE (Heath et al. 1969). The purpose of this article is to report on the nature of the DDE -shell thinning response in Colorado prairie falcons, and on its mathematical similarity to the phenomenon reported in peregrine falcons and in brown pelicans. Data are available on shell condition and residue levels for 30 prairie falcon eggs collected in 1967-68, and 10 collected in 1972. One egg was taken from each clutch. Eggs collected in 1967-68 were analyzed for p,p'DDE using essentially the method described in the USFDA Pesticide Analytical Manual and described elsewhere (Enderson and Berger 1968). Eggs taken in 1972 were analyzed for p,p'-DDE using an acid-celite column for extract cleanup. The lipid extracts of egg contents, obtained by soxhlet extraction for 8 hours in a 1:2 mixture of glass-distilled acetone and hexane, were dryed for 24 hours in an oven at 65 C, and weighed to obtain lipid weight. The weight of the dried lipid extract averaged 29.4 percent of the whole dry weight for the ten eggs. The extract was redissolved in acetone-hexane solvent and passed through a modified Davidow column (Stanley and LeFavoure 1965) consisting of celite, sulfuric acid, and fuming sulfuric acid, permitting rapid cleanup with quantitative recovery of the DDT compounds (Risebrough et al. 1970). This procedure destroys dieldrin. Blank samples of solvent carried through the entire procedure showed the presence of no substances that might interfere with the determination of DDE. The extracts were analyzed on a Varian Aerograph 6 00D gas chromatograph equipped with dual ovens and hydrogen-3 e ectron capture detectors. Each sample was run through glass columns containing 5 percent QF-1 on 80-100 mesh, acid washed, HMDS treated Chromosorb W, and 5 percent DC-200 on 100-200 mesh Varaport 30 to provide confirmation of DDE. In nearly all samples, DDE accounted for over 90 percent of the residues seen on the chromatograms, but only DDE 1 Study supported by the National Science Foundation through the College Science Improvement Program. We thank R. Olendorff and J. Stoddart for the use of their unpublished data. 476 J. Wildl. Manage. 37(4):1973 This content downloaded from 207.46.13.120 on Wed, 14 Sep 2016 05:41:42 UTC All use subject to http://about.jstor.org/terms RESIDUES IN PRAIRIE FALCONS ? Enderson and Wrege 477