Pesticide Analysis, Egg and Eggshell Characteristics of Red-Tailed Hawk Eggs

In this study, addled and viable Red-tailed Hawk eggs were compared in terms of pesticide levels, egg and eggshell parameters, and shell ultrastructure as determined by scanning electron microscopy. These values were then used to compare actual measurements against egg and eggshell indices commonly reported in the literature. Addled eggs of Red-tailed Hawks were of greater length, weight and volume than viable eggs, while viable eggs showed greater shell weights and thickness than addled eggs. The general structure of the eggshell consisted of 3 layers: shell membrane, mammillary layer and palisade layer. No cuticle was present. No differences in thickness of the shell membrane or mammillary layer were detected between addled and viable eggs; however, the palisade layer was found to be 24% thicker (X2, P<0.05) in viable eggs than in addled eggs (0.11 ±0.03 mm and 0.08±0.01 mm, respectively). The thicker palisade layer resulted in an overall thicker eggshell in viable compared to addled eggs (0.28±0.02 mm and 0.250.03 mm, respectively). Extensive areas of cavitation in the mammillary layer were found in many addled eggs, but never in viable eggs. Pore channels originating at the membrane layer could be seen extending to the outer surface of the egg. All egg samples analyzed for pesticide residues bore measureable amounts of PCB and DDE, while some samples contained dieldrin and heptochlor epoxide. OHIO J. SCI. 80(5): 206, 1980 During the past twenty years, numerous studies have reported residues of organochlorine insecticides in the eggs of wild birds, but few studies have concentrated on buteos. Seidensticker and Reynolds (1971) analyzed eggs of Redtailed Hawks in Montana and found measurable, but relatively low, levels of DDT, DDD, DDE, and dieldrin in all eggs tested. Heptochlor epoxide and PCB was found in some samples, and low levels of DDE were reported in Canadian Red-tailed Hawks (Postupalsky 1970). In both falconiforme and non-falconiforme birds, changes in parameters such as volume, size and shape have been related to geographical location and/or natural variation in egg sizes within clutches or species (Osborne and Winters 1977). Eggshell weight (Ratcliffe 1967) and eggshell thickness have been shown to be inversely proportional to residue levels in the egg (Anderson and Manuscript received 12 March 1979 and in revised form 5 October 1979 (#79-15). Hickey 1970). Through the use of scanning electron microscopy (SEM), structural changes in the eggshell have been shown to correlate with high pesticide levels in the egg of non-falconiforme birds (McFarland et al 1971, Jorgenson and Kraul 1974). The purpose of the present study was to compare addled and viable eggs of Red-tailed Hawks in terms of pesticide levels, egg and eggshell parameters, and shell ultrastructure. The values were then used to compare actual measurements against egg and eggshell indices commonly reported in the literature. MATERIALS AND METHODS Seventy addled Red-tailed Hawk eggs representing 63 clutches were randomly collected in 6 Ohio counties (Butler, Delaware, Franklin, Hamilton, Preble and Warren) and 3 counties in Kentucky (Boone, Pendleton and Timble) during 1967-77. Eight viable eggs representing 6 clutches were collected in 2 Ohio counties (Delaware and Butler) in 1978. Addled eggs were collected in Ohio during raptor censusing by Jack Holt and myself while addled eggs from Kentucky were collected by Jack Holt. After