Geology topics
Holliday H. Obrecht
Publications and source records attributed to Holliday H. Obrecht.
Description and identification of American Black Duck, Mallard, and hybrid wing plumage
We developed a key to identify wings of hybrids between American Black Ducks (Anas rubripes) and Mallards (A. platyrhynchos). Material for analysis included review of historical descriptions dating from the late 1700's, older museum collections in Europe and North America, wings collected from hunters in North America and Great Britain, birds banded in Canada and the United States, and a flock of propagated hybrids. All first filial generation (F1) American Black Duck - Mallard hybrids were identified correctly with the key. A lower proportion of other hybrid cohorts (i.e., backcrosses of F1 to parental forms (P1), and second and third filial generations (F2, F3, etc.) were identified. We successfully identified a larger portion of male than female hybrids for all hybrid progeny cohorts examined except F1. The new key identified 2.37 times more hybrids in the 1977 U.S. Fish and Wildlife Service Parts Collection Survey (annual determination of the species, age, and sex composition of the waterfowl harvest using detached wings contributed by hunters) than were identified by standard techniques. The proportion of American Black Duck - Mallard hybrids to the American Black Duck parental population (the ratio: hybrids/[hybrids + American Black Ducks]) may therefore be closer to 0.132 than 0.056, the historically reported value. The hybrid key is suggested for use from North Carolina north in the Atlantic Flyway and Arkansas and Tennessee north in the Mississippi Flyway (areas where other members of the Mallard group will not confound assessment). We provide suggestions for further research that would assist identification of wings in parts collection surveys and permit estimation of the proportional representation of Mallard genes in the American Black Duck gene pool.
Survival and band recovery rates of sympatric American black ducks and mallards
Banding and recovery data from American black ducks ( Anas rubripes ) and mallards ( A. platyrhynchos ) banded in the same breeding or wintering areas over the same time periods were used to estimate annual survival and band recovery rates. Recovery rates, based on preseason bandings, were very similar for sympatric black ducks and mallards and exhibited similar patterns of year-to-year variation for the 2 species. Tests for differences between the species in annual survival rates yielded equivocal results. We tentatively conclude that annual survival rates of mallards generally were not higher than those of black ducks banded in the same areas. The apparent difference in population status between black ducks and eastern mallards does not seem to result from differences in mortality rate. Nevertheless, we should attempt to identify management practices that might increase survival probabilities of black ducks.
Blood chemistry and hematocrit of captive and wild canvasbacks
Blood chemistry and packed cell volume (PCV) did not vary among groups of captive canvasbacks ( Aythya valisineria ) maintained ad libitum on 5 diets varying in metabolizable energy (ME) and protein. Ducks fed low quality diets increased their consumption so that all ducks were obtaining similar amounts of energy and protein. Some variables, including cholesterol, were found to differ between the sexes and ages of captive ducks. Seasonal differences were detected in the blood chemistry of captive canvasbacks. Four of the 5 enzyme values increased from October to January and then declined to April. PCV increased from 45 in October to 51 in April. Overall, blood chemistry values and PCV's were highly variable and did not appear to be good discriminators for age, sex, and diet of captive canvasbacks. Differences detected between captive and wild canvasbacks were attributed to increased stress of wild ducks during handling.