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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. J. WILDL. MANAGE. 50(3):435-441 Most studies dealing with avian blood have been conducted with chickens and other domestic birds (Lucas and Jamroz 1961, Sturkie 1976), and their emphasis has been on hematology rather than blood chemistry. Other studies have been conducted on the blood of birds other than Anseriformes (Ronald et al. 1968, Carey and Morton 1976, Rehder et al. 1982, Parrish and Mote 1984). Gee et al. (1981) compared differences in 25 blood chemistry values among 12 captive avian species; 7 of these were endangered species and included quail (Odontophorinae), raptors (Falconiformes), cranes (Gruidae), and geese (Anserini). Several researchers have demonstrated that the physiological condition of birds can influence blood values (Altman and Dittmer 1964, Dolnik 1973, Driver 1981). Gee et al. (1981) showed differences in blood values due to sex; however, Mulley (1979, 1980) was unable to demonstrate differences in blood chemistry and hematology due to sex with 2 duck species in Australia. Other researchers have shown the effect of age (Leonard 1969, Sturkie 1976). Woerpel and Rosskopf (1984) reviewed the use of blood chemistry as an aid in the diagnosis of disease and illness in caged birds. Several research studies have been conducted concerning factors affecting certain blood values of waterfowl. Wood and Hofman (1967) found that blood values of mallards (Anas platyrhynchos) could be influenced by artificial stimulation of reproduction, and Wood and Smoes (1968) reported the effects of reproducti e suppression on the blood of mallards. Mori and George (1978) studied seasonal effects on certain blood serum variables of Canada geese (Branta canadensis). Kocan (1972) conducted hematological analyses on 54 canvasbacks from Chesapeake Bay. Although PCV for male and female canvasbacks overlapped, there was a tendency for higher values in females (. = 53) than in males (9 = 51). In another sample of canvasbacks Kocan and Pitts (1976) reported higher PCV values in females than males although ages were not determined. They stated that differences observed among adult ducks probably reflected hormonal and nutritional differences brought about by changing photoperiod and migration. Hemm and Carlton (1967) reported conflicting PCV data in ducks due to age and sampling variability. More recent reports on waterfowl PCV values show little differences between sexes (Williams and Trainer 1971, Shave and Howard 1976, Mulley 1979). There are indications that differences in PCV exist between dabbling and diving ducks (Bond and Gilbert 1958, Shave and Howard 1976). The influence of nutrients on the blood chemistry of waterfowl has not been determined adequately. Newberne (1975) discussed the importance of diet in research experiments with regard to changing physiological processes, but he did not give specific examples of changes that occurred in blood due to diet. Most blood analyses conducted with waterfowl have been done with breeding ducks with emphasis

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. J. WILDL. MANAGE. 51(4):700-710 Black duck populations apparently have declined for the last 20-30 years (Winter survey data, U.S. Fish and Wildl. Serv. [FWS], Migratory Bird Manage. Off. [MBMO] files). Single factors have been suggested as "the cause" of the decline or "the problem" with black duck populations (Grandy 1983). The rate of change in population size of black ducks is a function of both survival and reproductive rates. An increase in survival rate or any component of reproductive rate would bring about an increase in the population rate of change. When viewed in this manner, it does not seem especially useful to expend effort trying to identify "the cause of decline" or "the problem with the population." Instead, we should be devoting our attention to factors that may influence black duck survival or reproductive rates and that may themselves be responsive to management efforts. Comparative studies may be useful in identifying factors that influence black duck population dynamics and that may be subject to change. Especially interesting would be temporal comparisons involving estimated survival or reproductive rates during recent years and during some period in the past when the population was thought to be stable. For the black duck interspecific comparisons with sympatric mallards may also be useful, since eastern mallard populations appear to be doing better than those of the black duck (see Collins [1974], Heusmann [1974], Dennis et al. [1984]). Blandin (1982: 165-166) called for such comparative studies and stated, "Greater insight into how the malThis content downloaded from 207.46.13.113 on Sun, 24 Apr 2016 05:18:13 UTC All use subject to http://about.jstor.org/terms J. Wildl. Manage. 51(4):1987 BLACK DUCKS AND MALLARDS * Nichols et al. 701 lard has succeeded so well within the black duck's traditional breeding range may provide information of management value as efforts continue to enhance the population status of the black duck." One comparison of survival and hunting mortality rate estimates for mallards and black ducks has been made and has drawn considerable attention. Blandin (1982) estimated the proportion of annual mortality in black ducks attributable to hunting and compared these estimates with those presented by Anderson (1975) for mallards. The point estimates were higher for black ducks than mallards, especially for adult females and young birds (Blandin 1982). Although Blandin (1982) appropriately qualified his discussion of this comparison and what it meant, others have used the comparison as a basis for drawing inferences about the effect of hunting on black ducks (Grandy 1983). Krementz et al. (in press) used more recent data for black ducks and also compared their estimates of both annual mortality and mortality attributable to hunting to the mallard estimates from Anderson (1975). Their average estimates of annual mortality for black ducks appeared higher than those for mallards for all age-sex classes, whereas apparent interspecific differences in harvest and kill rates were not consistent among the 4 age-sex classes. Although representing an important first step, these comparisons were of mallard data from throughout North America and black duck data from eastern North America. In addition, the comparisons were not restricted to the same period of years for both species. Heusmann (1981) estimated survival and band recovery rates for park mallards and coastal black ducks banded during winter in Massachusetts, 1971-76. Band recovery rates did not differ between the 2 species for either males or females. Survival rates of male black ducks and mallards were similar, but survival rates of female black ducks were significantly higher than those of female mallards (Heusmann 1981). In the present work, we selected breeding and wintering areas in eastern North America, in which both mallards and black ducks were banded during the same years. We then estimated survival and band recovery rates of these birds and tested the hypothesis of no difference. The principal research question we addressed was, "Do sympatric mallards and black ducks exhibit the same average survival and recovery rates?" We also asked the secondary question, "Do recovery and survival rates of sympatric mallards and black ducks exhibit similar patterns of temporal variation; e.g., in years when mallard survival rates are high, are black duck survival rates also relatively high, and vice versa?" We benefitted from discussions about black duck population dynamics with M. J. Conroy, D. G. Krementz, R. I. Smith, and most importantly, the late W. W. Blandin. We thank F. D. Caswell, M. J. Conroy, D. H. Johnson, K. H. Pollock, M. D. Samuel, and J. R. Serie for providing constructive comments on an earlier draft of the manuscript. We followed most, but not all, of their suggestions, and we bear sole responsibility for the content of the manuscript. We thank A. Cyphers, J. Armstrong, and R. Jones for typing the manuscript. Finally, we thank the many banders of mallards and black ducks whose data form the basis for this work.