Eggshell Breakage by Incubating Black Ducks Fed DDE

Abstract

Black duck (Anas rubripes) hens fed 10 ppm dry weight (approximately 3 ppm wet weight) of p,p'-DDE in the diet laid eggs with shells 22 percent thinner at the equator, 30 percent thinner at the cap, and 33 percent thinner at the apex than those of controls. Natural incubation increased shell cracking more than fourfold as compared with mechanical incubation. Hens removed cracked eggs from nests, and one hen terminated incubation. Hens fed DDE produced one-fifth as many ducklings as controls. DDE in eggs of dosed hens averaged 64.9 ppm wet weight. J. WILDL. MANAGE. 37(3):390-394 Field observers have reported that eggs of raptors, gulls, and pelicans have been cracked, crushed, and sometimes eaten by parent birds (Ratcliffe 1958, 1960; Ludwig and Tomoff 1966, Jehl 1969, Keith et al. 1970). A close association between egg destruction and organochlorine residues has usually been noted (Ratcliffe 1967, Hickey and Anderson 1968, Fyfe et al. 1969, Cade et al. 1971, Blus et al. 1972). Eggs of kestrels (Falco sparverius) fed dieldrin and DDT in combination disappeared from nests in greater proportion than eggs of controls (Porter and Wiemeyer 1969). Egg loss was attributed to breakage of thin-shelled eggs and egg eating by the adults. Black ducks fed either 10 or 30 ppm of DDE (dry weight) in the diet laid eggs which had thinner shells and cracked more readily than controls (Longcore et al. 1971). Since eggs were gathered daily and placed in mechanical incubators, the effects of natural incubation were not evaluated. In the present study, black ducks were allowed to nest as pairs in individual pens to approximate a natural nesting cycle and to compare shell cracking and hatching success of eggs incubated by nesting hens and those incubated mechanically. We acknowledge R. J. Diebolt for his care of these ducks; R. G. Heath advised on statistical procedures; R. Andrews and L. F. Stickel reviewed the manuscript; and E. H. Dustman contributed to initial study design. MATERIALS AND METHODS The black ducks used in this study were 2-year olds that had bred successfully in 1970 (Longcore et al. 1971). Ten pairs had received dietary dosage of 10 ppm of p,p'DDE (approximately 3 ppm wet weight) from mid-November 1969 to mid-June 1970 and untreated food from mid-June 1970 to mid-November 1970, when dosage was resumed. Ten pairs of controls received untreated commercial duck breeder mash throughout. Details of pen facilities and food preparation are discussed by Longcore et al. (1971). At the onset of egg laying about 5 months after initiation of dosage, nests were visited daily and eggs were numbered and examined for cracks. After completion of laying, eggs were examined for cracks at weekly intervals. Hens were allowed to incubate until they had exceeded the normal incubation period. Eggs were then removed and examined to ascertain development. The third egg laid by each hen was removed from the clutch to obtain shell measurements and residue analysis. Shells 1 Present address: Department of Zoology, Utah State University, Logan 84321. 390 J. Wildl. Manage. 37(3):1973 This content downloaded from 40.77.167.7 on Sat, 16 Jul 2016 05:28:11 UTC All use subject to http://about.jstor.org/terms EGGSHELL BREAKAGE BY BLACK DUCKS * Longcore and Samson 391 were washed while maintaining membranes intact and air-dried to constant weight. Shell thickness was measured at the shell equator, cap, and apex with a micrometer graduated in 0.01 mm units. Shell surface area was determined by the methods of Romanoff and Romanoff (1949:110), and shell weight per unit area was calculated. Egg contents were analyzed for organochlorine pesticides and PCB's by WARF Institute, Inc., using gas chromatography. Egg contents were dried and ground with sodium sulphate; extracted with a mixture of ethyl ether and petroleum ether (70:170) for 8 hours in Soxhlet apparatus; cleaned and separated by two elutions through a Florisil column with ethyl ether and petroleum ether (3:97; 15:85). Analysis was by gas chromatography, using a Barber-Coleman Pesticide Analyzer Model 5360. Columns were glass, 1.219 m x 4 mm. For the first elution, the column packing was 5 percent DC 200 Gas Chrom Q (60/80 mesh); temperatures were: injector 230 C, column 200 C, and detector 240 C. For the second elution, packing was 3 percent OV-17 on Gas Chrom Q (80/100 mesh); and temperatures were: injector 230 C, column 200 C, and detector 240 C. Nitrogen flow rates were such that p,p'-DDT had a retention of 6-8 minutes. For PCB separation an aliquot of the first elution was placed on silicic acid-Celite column (Armour and Burke 1970). Typical elutions were petroleum ether followed by 1:19:80 solution of acetonitrile:hexane:di-