Canvasbacks Research Articles

Food Defendability and Antipredator Tactics: Implications for Dominance and Pairing in Canvasbacks

Etude des agressions alimentaires chez Aythya valisineria au cours des migrations de printemps et d'hiver dans divers habitats de Caroline du Nord et facteurs affectant le cout et le benefice du maintien des couples en dehors de la reproduction

Interspecific differences in bill and tongue morphology among diving ducks (Aythya spp., Oxyura jamaicensis)

Twelve morphological characters of the bill and tongue were measured in six species of diving ducks (Aythya and Oxyura spp.). We used multivariate analyses to describe interspecific differences in morphology and related these differences to published information about food habits and feeding behavior of the six species. Canvasbacks (Aythya valisineria) have long, narrow, deep bills that are well suited to probing and grasping plant tubers from the substrate. Greater (A. marila) and Lesser Scaup (A. qffinis) and Ruddy Ducks (Oxyura jamaicensis) have short, wide, shallow bills suited to straining food items. Lesser Scaup and Ruddy Ducks have the greatest lamellar density and this enables them to strain very small plant and animal material. Redheads (A. americana) and Ring-necked Ducks (A. collaris) have bills of intermediate size and shape that are suited to straining seeds and grazing leafy parts of plants. Lesser and Greater Scaup, on the basis of bill morphology, are more similar to Ruddy Ducks than they are to other Aythya species. Overall, bill size and shape were more important in distinguishing the six species than were lamellar density or tongue characteristics.

Distributional Responses of Canvasback Ducks to Weather and Habitat Change

In order to investigate the effects of different irrigation and fertilization on soil microbial properties of summer maize field, we used ZN99 with high nitrogen use efficiency as the test material. The experiment adopted the split plot design which included two irrigation levels (526 mm and 263 mm) as the main plots, three fertilizer types (U, M, UM) and two fertilizer levels (N 100 kg . hm-2 and 200 kg . hm-2) as the subplots. The results showed that the irrigation level affected the regulating effects of fertilizer on soil microbial biomass (carbon and nitrogen) and microbial di- versity. The organic fertilizer application must be under the sufficient irrigation level to increase the soil MBC (14.3%-33.6%), MBN (1.8-2.3 times) and abundance significantly. A moderate rate of irrigation, higher rates of organic fertilizer application or organic manure combined with inorganic fertilizer could increase the nitrogen-fixation species and quantity of Firmicutes, γ-Proteobacteria and α-Proteobacteria in the soil. Under the same N level, there was no significant difference of grain yield between organic manure and inorganic fertilizer treatments. Considering sustainable production, proper organic manure application with moderate irrigation could increase the quantity of the soil microbial biomass and microbial diversity, and improve the capacity of soil to supply water and nutrients.

Winter Survival of Female American Black Ducks on the Atlantic Coast

We used radio telemetry to monitor the winter survival and cause-specific mortality of 227 female American black ducks (Anas rubripes) captured in New Jersey and Virginia, 1983-85. Mean survival rate for 19 December-15 February was 0.65. Survival from hunting and nonhunting risk was 0.84 and 0.78, respectively. Causes of nonhunting mortality included predation and emaciation (winter stress). After-hatchyear (AHY) ducks had a higher probability of survival than hatch-year (HY) ducks (0.73 vs. 0.60); most of this difference was related to survival from nonhunting risk. After-hatch-year ducks with body masses > median had a higher survival probability (0.85) than AHY ducks with < median body masses (0.61) because of differential survival from hunting risk. Hatch-year ducks had lower body mass than AHY ducks, but among HY ducks body mass was not related to survival. There were no consistent patterns in survivorship in relation to mean daily temperature, although the timing of the onset of low temperatures and storms may have influenced movement patterns. Our estimated survival rates are consistent with estimates from other studies of seasonal and annual survival. It may be possible to manage habitats for population segments at high risk (HY and low body mass birds), and increase black duck survivorship. J. WILDL. MANAGE. 53(1):99-109 Populations of American black ducks have declined from the 1950's to present (Barske 1968, Grandy 1983, Feierabend 1984). Reasons for the decline are unknown but may be related to specific causes of mortality such as hunting (Blandin 1982, Krementz et al. 1988), predation (Ringelman and Longcore 1983), competition from and hybridization with mallards (Anas platyrhynchos) (Johnsgard 1961, 1967), and habitat losses (Barske 1968). Winter is a critical time for black ducks, because of high energetic demands (Albright 1981, Reinecke et al. 1982). Reinecke et al. (1982) demonstrated that immature females achieved adult structural size, but were lighter in weight and had smaller nutrient reserves than did adults during their first winter. Other studies have corroborated a link between age, body condition, and probability of survival. Hepp et al. (1986) reported that the probability of being shot by hunters for mallards in poor condition was higher than for those in better condition. Haramis et al. (1986) reported a direct relationship between the body mass of canvasbacks (Aythya valisineria) in early winter and probability of surviving the winter. Although immature black ducks are more vulnerable to hunting (Schierbaum and Foley 1957, Krementz et al. 1988), and have lower annual survival rates than do adults (Blandin 1982, Krementz et al. 1987), whether age-specific mortality persists through winter, or occurs primarily during the postfledging period and early hunting season is unknown. Managers need estimates of winter survival rates and identification of mortality sources to understand black duck population dynamics and assist in the management of black duck populations. Our objectives were to estimate survival rates of black ducks during winter, examine specific components of mortality, specifically hunting versus nonhunting mortality, and examine variation in survival rates during winter in relation to age, body condition, time, geographic location, and weather conditions. We appreciate the assistance of E. L. Derleth, N. Dietz, B. Dirks, B. L. Estel, S. Holzman, A. G. Larochelle, J. M. Morton, H. H. Obrecht III, S. R. Perin, N. Phelps, H. G. Russell, M. A. Spoden, J. M. Walsh, and G. Wright in the collection of field data. We also thank F. Ferrigno, New Jersey Fish and Game, G. L. Inman and D. L. Beall of Forsythe National Wildlife Refuge, and D. Holland of Chincoteague National 'Present address: Georgia Cooperative Fish and Wildlife Research Unit, School of Forest Resources, University of Georgia, Athens, GA 30602.

Body Weight and Composition Dynamics of Fall Migrating Canvasbacks

We studied body weights and composition of canvasbacks (Aythya valisineria) during fall migration 1975-77 on stopover sites along the upper Mississippi River near La Crosse, Wisconsin (Navigational Pools 7 and 8) and Keokuk, Iowa (Navigational Pool 19). Body weights varied (P < 0.001) by age and sex without interaction. Weights varied by year (P < 0.001) on Pools 7 and 8. Mean weights increased (P < 0.01) within age and sex classes by date and averaged 3.6 and 2.7 g daily on Pools 7 and 8 and Pool 19, respectively. Percent fat was highly correlated (P < 0.001) with carcass weight for each age and sex. Live weight was a good predictor of total body fat. Mean estimated total body fat ranged from 200 to 300 g and comprised 15-20% of live weights among age and sex classes. Temporal weight patterns were less variable for adults than immatures, but generally increased during migration. Length of stopover varied inversely with fat reserves among color-marked adult males. Variation in fat condition of canvasbacks during fall may explain the mechanism regulating population ingress and egress on stopover sites. Fat reserves attained by canvasbacks during fall stopover may have adaptive significance in improving survival by conditioning for

Reproductive Activity of Force-Paired Cockatiels (Nymphicus hollandicus)

Reproductive Activity of Force-Paired Cockatiels (Nymphicus hollandicus)

Molt in the Annual Cycle of Canvasbacks

Abstract We studied the intensity of molt of capital, down, and contour plumages of male and female Canvasbacks (Aythya valisineria) from late fall through winter, spring migration, and nesting. Molt intensities in both juvenile and adult males were highest among arriving fall migrants and during prewinter fat deposition, and molt in juvenile males increased during early spring migration. Among females, capital molt was high among arriving migrants in fall, and molt of all plumage types increased during spring migration and courtship. Paired females tended to molt more heavily than unpaired females during spring migration, but many females initiated intensive prebasic molt before pairing. Molt in females peaked in spring migration and early breeding, concurrently with accelerated fat storage and ovarian growth. Capital and contour molt in females decreased during laying and essentially ceased during incubation, perhaps to mitigate energetic constraints during these periods. Prewinter nutrient storage appeared independent of molt intensity, except for body protein among juveniles. During spring migration, molt intensities were greater in adult females with higher levels of body fat and protein, indicating that molt did not necessarily precede or interfere with nutrient storage. We suggest that outside the laying, incubation, and wing molt periods, the energetic costs of molt in Canvasbacks are not sufficient to mandate temporal separation of molt from nutrient storage, migration, courtship, or early stages of rapid ovarian growth.

Food Habits and Distribution of Wintering Canvasbacks, Aythya valisineria, on Chesapeake Bay

Baltic clams (Macoma balthica) were the predominant food items of 323 canvasbacks (Aythya valisineria) collected throughout Chesapeake Bay during 1970–1979. Natural vegetation constituted 4% of the food volume. Widgeongrass (Ruppia maritima) and redhead grass (Potamogeton perfoliatus) constituted the greatest percent volume and frequency of occurrence among the plant species, whereas wild celery (Vallisneria americana) constituted only a trace of the food volume. These results contrast with historical records of food habits of canvasbacks in Chesapeake Bay. Canvasback population estimates during the 1970’s were examined to detect annual and seasonal changes in distribution. Linear regression analyses of winter canvasback populations in the bay showed a significant decline in the upper-bay and middle-bay populations, but no significant changes in the lower-bay and Potomac River populations. The changes in winter distribution and abundance of the canvasback appear related to changes in natural food availability, which is the result of altered environmental conditions.

Effect of the Point System on Redistributing Hunting Pressure on Mallards

Effectiveness of the point system was investigated by contrasting first-year recovery rates of mallards (Anas platyrhynchos) during the pre-point system period (1960-69) and during a point system period (1972-84). Three components were examined to investigate effectiveness of the point system: decreasing recovery rates of females, increasing recovery rates of males, and increasing the difference between male and female recovery rates. We concluded that little change in recovery rates of male and female mallards took place since initiation of the point system. Lacking a controlled experiment, it was not possible to attribute the small changes we did find to point system regulations, or to discern whether the reduction in female recovery rates was the result of the point system. J. WILDL. MANAGE. 52(1):89-94 The point system was suggested as a method for regulating the harvest of waterfowl (A. S. Hawkins and C. E. Addy, unpubl. rep., U.S. Fish and Wildl. Serv., Washington, D.C., 1971). Low point values were assigned to species or sex classes for which additional hunting pressure was desirable (e.g., drake northern pintails [Anas acuta] were assigned 10-20 points each) and high point values were assigned to those for which less hunting pressure was desired (e.g., canvasback [Aythya valisineria] were valued at 100 points). The daily bag limit was reached when a hunter bagged a bird causing the total point value of birds in possession to equal or exceed 100 points. The objectives of the point system were to afford waterfowl managers the ability to redistribute harvest among species or sexes within a species and to provide more flexible harvest regulations to increase hunting opportunities (Geis This content downloaded from 157.55.39.35 on Fri, 02 Sep 2016 04:18:09 UTC All use subject to http://about.jstor.org/terms 90 EFFECT OF POINT SYSTEM ON MALLARDS * Rexstad and Anderson J. Wildl. Manage. 52(1):1988 and Crissey 1973). The reduction in the harvest of females theoretically allowed females to contribute to the reproductive pool the following spring. Thus, a strong premise underlying the point system is that hunting mortality is additive (Nichols et al. 1984). Interest in the point system was low initially but increased rapidly as the potential advantages of the system were realized. Controversy followed, which centered on regulation enforcement. Enforcement was difficult because a hunter could initially shoot a 100-point bird but continue to hunt low-point birds (Geis and Crissey 1973). For example, 2 35-point birds and a 20point bird might subsequently be taken, and hunters could claim they shot the 100-point bird last. This procedure, known as reordering, also could apply to individuals within a hunting party. A second problem was the potential for waste of high-point birds either discarded in the marsh or deliberately not retrieved so the hunter could continue to shoot lower-point birds and thus extend the hunting opportunity. Prior to the initiation of the point system there was little incentive for hunters to leave birds in the marsh. Most states changed from a conventional bag limit to the point system by the 1971-72 hunting season in the Central Flyway and by the 197475 season in the Mississippi Flyway. Canadian provinces, the Pacific Flyway states, and many states in the Atlantic Flyway never adopted the point system. Only North Dakota in the Central and Minnesota in the Mississippi flyways retained conventional bag limits and some states (e.g., Oh.) have returned to the conventional bag limits. Initial evaluations of the point system were conducted in Colorado (Hopper et al. 1975) and Michigan (Mikula et al. 1972). Most studies were directed at hunter attitudes and acceptance (Nelson and Low 1977) and hunter performance in the field (C. F. Kimball et al., unpubl. rep., U.S. Fish and Wildl. Serv., Washington, D.C., 1971; Bishop 1973). Our objective was to determine if the point system was effective in redistributing hunting pressure toward male mallards (ranging in value from 20 to 35 points) and away from female mallards (ranging in value from 70 to 90 points). We are grateful to the Pacific Flyway Council for providing funds to conduct this analysis. We acknowledge the assistance of the U.S. Fish and Wildlife Service Bird Banding Laboratory, Laurel, Maryland and the duck hunters who reported their recovered bands. We thank T. W. Aldrich for facilitation and logistical support, and W. F. Andelt, J. C. Bartonek, K. E. Gamble, D. H. Johnson, C. F. Kimball, H. W. Miller, J. D. Nichols, and J. T. Ratti for their helpful comments on earlier versions of this manuscript.

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. 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

Age-Class Determination of Ring-Necked Ducks

A quantitative technique was developed to distinguish adult from yearling ring-necked ducks (Aythya collaris) during the breeding season using wing feather criteria. This method requires removal and measurement of the 5th secondary (S 5) and 12th greater secondary covert (GSC 12). Bursal and other plumage characteristics were evaluated for use in the field during the breeding season. Cloacal characteristics are of no value in distinguishing adult and yearling males after arrival on breeding areas (Apr), but bursal depth >10 mm is characteristic of yearling females into their Ist breeding season. Although not all adult females have white head feathers (e.g., flecking), the presence of flecking on mature females strongly indicates adult status. J. WILDL. MANAGE. 50(3):442-445 The ability to distinguish age classes within waterfowl populations is important in understanding aspects of their reproductive biology and population dynamics (Serie et al. 1982). However, determining age classes of waterfowl that reproduce in their 1st year often is difficult, especially during the breeding season. Cloacal (Gower 1939) and rectrix (Pirnie 1935) characteristics are commonly used during the fall and winter to distinguish immatures from adults but are unreliable for birds captured in spring (Hochbaum 1942). Use of qualitative wing feather criteria for determining age class and sex is possible for some species: mallards (Anas platyrhynchos) (Krapu et al. 1979, Gatti 1983), blue-winged teal (A. discors) (Dane 1968), American wigeons (A. americana) (Wishart 1981), canvasbacks (Aythya valisineria) (Serie et al. 1982), and redheads (A. americana) (Dane and Johnson 1975). Unfortunately, these methods do not work well for ring-necked ducks (Carney 1964). Remiges and associated coverts are retained by juvenile waterfowl until the prebasic II molt and are replaced annually thereafter during the prebasic molt (Humphrey and Clark 1961). Multivariate statistical procedures using wing feather measurements have been used to determine age of springand summer-caught mallards (Krapu et al. 1979, Gatti 1983), gadwalls (Anas strepera) (Blohm 1977), American wig ons (Wishart 1981), canvasbacks (Serie et al. 1982), and redheads (Dane and Johnson 1975). Here we describe a quantitative technique for accurate age class separation of male and fema e ring-necked ducks in spring and early summer. Additionally, bursal and other plumage characteristics are evaluated for use in the field during the breeding season. We wish to thank B. D. J. Batt, R. D. Crawford, and M. W. Weller for their helpful comments on earlier drafts of the manuscript. We were assisted in the field or laboratory by J. S. Barzen, D. O. Carlson, L. A. Fluggeman, and J. W. Grimm. Financial support was provided by the North Am. Wildl. Found. through the Delta Waterfowl and Wetland Res. Stn., Univ. Minnesota (Dep. Fish. and Wildl., Comput. Cent., Agric. Exp. Stn., and Graduate School), Minn. Dep. Nat. Resour., and Minn. Waterfowl Assoc. This is J. Pap. 13837 of the Minn. Agric. Exp. Stn., St. Paul, Minn.

Influence of Nutrients on Feed Intake and Condition of Captive Canvasbacks in Winter

Dramatic changes in the food habits and distribution of canvasbacks (Aythya valisineria) in Chesapeake Bay during the 1970's generated a need to evaluate the nutritional value of food items and the requirements of this species on its wintering grounds. Groups of captive canvasbacks were maintained ad libitum on 5 diets during the winters of 1978-79 and 1979-80 to evaluate the effects of varying protein and energy levels on feed intake and condition. Feed intake during the 1979-80 winter was 42% greater for those ducks fed the low energy (1,543 kcal/kg) diet than for those fed the high energy (3,638 kcal/kg) diet. Canvasbacks fed the high energy diet, however, consumed 317 kcal/bird day, whereas those fed the low energy diet consumed only 191 kcal/bird day. Body weight of males and females did not differ among groups fed different diets, but there were seasonal differences (P < 0.05) for both sexes aggregated across diets. Data from this study indicate that canvasbacks may be unable to adjust intake rates to compensate for low energy foods and subsequently may store less fat or modify behavior. However, decreased weight, feed intake, and activity of ducks fed ad libitum rations occurred in mid-winter irrespective of diet quality and appeared to be an endogenous component of their annual cycle that persists in captivity. These changes apparently have a selective advantage of increasing the probability of survival in ducks by decreasing energy expenditure during periods of winter stress. J. WILDL. MANAGE. 50(3):427-434 Aerial winter waterfowl surveys conducted by the U.S. Fish and Wildlife Service from 1955 to 1979 indicated that the winter population of canvasbacks in North America has ranged from 481,000 in 1955 to 179,000 in 1972 (Perry et al. 1981). The winter population in Chesapeake Bay (Md. and Va.) averaged 31% of the North American population and 62% of the Atlantic Flyway population. During 1955-79, numbers of canvasbacks declined substantially in Chesapeake Bay, the Atlantic Flyway, and North America (Perry et al. 1981). During the 1970's in the Atlantic Flyway, the percent of canvasbacks wintering in Chesapeake Bay decreased, whereas percentage increases occurred in New Jersey and North Carolina. Increases in New Jersey remain unexplained (Perry 1982), but increases in North Carolina may be related to better habitat conditions due to a larger number of freshwater impoundments (Perry and Uhler 1982). These wetlands provide abundant aquatic vegetation, which has traditionally been an important winter food for canvasbacks. Vegetation surveys from 1971 to 1979 showed Present address: 7 Crestwood Drive, Tolland, CT 06084. a decline in the frequency of occurrence and biomass of submerged aquatic plants in Chesapeake Bay (Kerwin et al. 1976, Bayley et al. 1978, Orth and Moore 1981, Haramis and Carter 1983). Turbidity and herbicides have been implicated in the decline of vegetation (Stevenson and Confer 1978). Two exotic aquatic plants, waterchestnut (Trapa natans) and spiked watermilfoil (Myriophyllum spicatum) were introduced into Chesapeake Bay during the 1900's and competed with native food plants (Gwathney 1945, Rawls 1975, Bayley et al. 1978). Some areas of the bay became completely covered by exotics, which restricted growth of wildcelery (Vallisneria americana) and other submerged native plants. Native waterfowl plant foods declined in abundance during the exotic plant infestations but recovered with the demise of the exotics. Waterfowl abundance on the Susquehanna Flats, in the upper bay, seemed to be inversely related to the abundance of exotic plants (Bayley et al. 1978). Habitat changes in Chesapeake Bay were reflected in a precipitous decline in vegetation as a food of canvasbacks, which occurred concurrently with an increase of mollusks as a food item (Munro and Perry 1981, Perry et al. 1981). The dramatic change in canvasback food habits

The Relationship Between Body Mass and Survival of Wintering Canvasbacks

Abstract Mass and recapture histories of 6,000 Canvasbacks (Aythya valisineria) banded in upper Chesapeake Bay were used to test two hypotheses: (1) early-winter body mass is associated with the probability of surviving the winter, and (2) early-winter body mass is associated with annual survival probability. Data were analyzed by a binary regression method that treated mass as a continuous variable and estimated parameters to describe a general relationship between body mass and survival probability. Results for adult males, which provided our largest data sets, presented strong evidence that birds with high relative early-winter masses had both greater overwinter and annual survival probabilities. Results of overwinter analyses necessarily are qualified by the alternative explanation of mass-dependent emigration, i.e. the possibility that lighter birds move south in response to cold weather and leave only heavy birds for recapture. Such a phenomenon remains to be documented. Results concerning annual survival probabilities are not vulnerable to this alternative explanation because of the strong fidelity of Canvasbacks at the banding site. Because of small sample size, data were inadequate to permit mass/survival inferences for adult females. Sample sizes were adequate for young Canvasbacks, but the results were less consistent than for adult males. Although early-winter body mass was associated positively with overwinter as well as annual survival for young Canvasbacks in some years, we suspect that the lack of established wintering patterns among these birds may underlie the less consistent result.

Polygyny in Barrow's Goldeneye

Polygyny in Barrow's Goldeneye

Foods of Canvasbacks and Redheads in Nevada: Paired Males and Ducklings

The diets of canvasback (Aythya valisineria) and redhead (A. americana) paired males and ducklings were the same as those of their mates and hens, respectively, during 1980-81 on Ruby Lake National Wildlife Refuge (RLNWR), Nevada. Diets of canvasback ducklings were high in protein and energy, but those of redhead ducklings were low. J. WILDL. MANAGE. 50(2):199-203 Paired male ducks and ducklings may have different food requirements than accompanying females. Paired males during the prelaying and laying period engage in defense of the female and a feeding territory (Dwyer 1974, Ashcroft 1976) and presumably should require high energy foods. Female ducks consume foods high in energy prior to nesting for deposition of energy reserves (Krapu 1974, 1981; Serie and Swanson 1976; Drobney 1980, 1982) and during the postlaying period to replace lipid stores exhausted during egg laying and incubation (Krapu 1974, Drobney 1982). Foods high in protein content are consumed during laying to meet the needs for egg formation (Krapu 1974, Drobney 1982). Thus, at least during the laying period, paired males and females may have different food requirements. Likewise, ducklings, which require foods high in protein for growth (Marshall 1951, Krapu and Swanson 1978), may need to consume different foods than brooding females that need foods high in energy, at least early in the brooding period. Molting for adult females may begin in the late stages of the brooding period, requiring foods high in protein content (Krapu and Swanson 1978). As part of a study on diet and nutrition of breeding canvasbacks and redheads (Noyes 1983, Noyes and Jarvis 1985), we determined if paired males and ducklings consumed diets different from associated adult females in response to differing nutritional requirements. This study was funded by the U.S. Fish and Wildl. Serv. through the North. Prairie Wildl. Res. Cent. and conducted under the auspices of the Oreg. Coop. Wildl. Res. Unit. We thank S. H. Bouffard, T. J. Bowser, F. W. Cameron, R. W. Carmichael, D. L. Eisele, P. A. Frazier, and C. L. Noyes for field and laboratory assistance. Other helpful assistance was provided by K. W. Cummins, L. R. D. Johnston, and R. L. Post for plant and invertebrate identification; E. R. Beals and C. L. Noyes for computer and statistical analyses; and J. R. Serie for helpful comments duri g the study. J. A. Crawford, D. S. Gilmer, G. L. Krapu, and D. E. Sharp reviewed early drafts of the manuscript. This is Oreg. Agric. Exp. Stn. Tech. Pap. 7425.

Variation in digestive organ size among five species of diving ducks (Aythya spp.)

Ceca length, small intestine length, and gizzard weight were measured for individuals of five species of diving ducks collected at Long Point Bay, Lake Erie, and Mitchell's Bay, Lake St. Clair, Ontario, in the falls of 1982 and 1983. The five species were Lesser Scaup (Aythya affinis, N = 84), Ring-necked Duck (Aythya collaris, N = 57), Greater Scaup (Aythya marila, N = 54), Redhead (Aythya americana, N = 58), and Canvasback (Aythya valisineria, N = 112). The diets of these species reportedly differ in diversity as well as in amount of fibre, and interspecific differences in gut morphology, not explained by differences in body weight, were accounted for by general differences in diet. Canvasbacks, although the heaviest species, had the shortest ceca, short intestines and light gizzards, presumably because their diet contains the least fibre. Conversely, the relatively small-bodied scaup species had the longest small intestines, likely because of their diverse diets which include animal and plant material. Our results show that morphological differences in waterfowl guts reflect dietary differences at a particular time and location and also illustrate the importance of adjusting gut measurements to body weight before making interspecific comparisons.

The need for accuracy in modelling: An example

The need for accurate information in modelling depends on the objectives of the effort, but trustworthy data are essential for a model intended for use in the management of natural resources. This point is illustrated by referring to a recently published model of canvasback ducks. We demonstrate that several key assumptions are not supported by biological evidence, and that inferences drawn from the mmodel could be dangerously misleading if they were used to guide the management of canvasback ducks.

Seasonal variation in pituitary responsiveness to luteinizing hormone-releasing hormone of mallards and canvasbacks

Endocrine profiles of wild mallards ( Anas platyrhynchos) and canvasbacks ( Aythya valisineria) were determined during the spring and the summer. Males and females of each species were treated with a single intravenous injection of 12 μg of synthetic luteinizing hormone-releasing hormone (LHRH). Preinjection and postinjection blood samples were collected and LH levels were determined by radioimmunoassay. LHRH evoked a brisk and significant elevation in serum LH in all ducks indicating the pituitary glands of both species contain readily releasable pools of LH. In March, the preinjection baseline levels of LH in the two groups did not differ. However, mallards responded to LHRH with a twofold increase in serum LH, while canvasbacks responded with a fourfold increase ( F = 17.1, P < 0.001). At the summer blood sampling period, mallards had significantly higher circulating levels of serum LH than canvasbacks ( F = 35.9, P < 0.001). Both species responded to LHRH with a twofold increase in circulating LH. These data indicate that seasonal variations in reproduction whown by the two species in captivity may be associated with differences in LHRH-sensitive pools of LH.

Diet and Nutrition of Breeding Female Redhead and Canvasback Ducks in Nevada

Diet, nutrition, and foraging strategies of breeding female canvasback (Aythya valisineria) and redhead ducks (A. americana) were studied by collecting foraging birds in 1980 and 1981 at Ruby Lake National Wildlife Refuge (Ruby Lake NWR). Female canvasbacks consumed a small number of food items, most of which were not abundant in the marsh. The diet of redheads changed with each stage of the reproductive cycle; they usually foraged on the most abundant foods in the marsh. Nutrient and energy content of the diet of canvasbacks varied little from laying through brooding, but both were quite variable in the diet of female redheads. Female canvasbacks retained large lipid reserves during formation of the clutch but used 68% from late laying to the incubation stage. Redheads expended 46% of their lipid reserves during formation of the clutch and 30% from late laying to incubation. J. WILDL. MANAGE. 49(1):203-211 Food habits and changes in body reserves of breeding waterfowl have received much attention, especially for dabbling ducks (Anas spp.) (Krapu 1974, 1981; Swanson et al. 1974b; Serie and Swanson 1976), wood ducks (Aix sponsa) (Drobney and Fredrickson 1979), and geese (Chen, Branta) (Harwood 1977; Ankney and MacInnes 1978; Raveling 1979). Generally, lipid reserves are accumulated before laying as a result of consumption of plant foods high in carbohydrates. During laying, females feed on foods high in protein (invertebrates by ducks, sprouting grasses by geese) to supply the protein necessary for egg production, and begin to utilize their lipid reserves. Restriction of food intake during incubation results in rapid depletion of lipid reserves. By the end of the incubation period, females have nearly exhausted their lipid reserves. The diet and nutrient cycles of breeding diving ducks (Aythya spp.), which feed to a greater extent on animal foods throughout the year than do dabbling ducks (Cottam 1939, Martin et al. 1951), have not been reported. W investigated the relationship between diet and body reserves of two closely related species of diving ducks, the redhead and the canvasback. These two species occur together over much of their range and have similar habitat r quirements during the breeding season (Weller 1959). However, they pursue different nesting strategies: the redhead is semiparasitic, whereas the canvasback is not (Weller 1959). Thus, their foods and nutrient cycles during the br eding season might be expected to be different, even when both species occur in the same marsh. The objectives of this study were to: (1) determine the foods consumed, preference for foods, and nutrient content of the diet of female canvasbacks and redheads; (2) determine changes in body weight and body reserves durIPresent address: 6132 SW 46th Ave., Portland, OR 97221. This content downloaded from 157.55.39.120 on Mon, 05 Sep 2016 06:18:07 UTC All use subject to http://about.jstor.org/terms 204 REDHEAD AND CANVASBACK DIETS * Noyes and Jarvis J. Wildl. Manage. 49(1):1985 ing reproduction; and (3) relate diet and changes in body reserves to their respective nesting

Effects of male courtship and gonadal steroids on pair formation, egg‐laying, and serum LH in Canvasback ducks (Aythya valisineria)

The effects of social stimuli on the reproductive physiology of female birds have been widely studied. This study examined the endocrine and behavioural responses of female Canvasbacks (Aythya valisineria) to changes in the behavioural and endocrine states of the male, as signalled by his courtship displays. Male Canvasbacks exposed to female conspecifics exhibited a variety of courtship displays which increased significantly with testosterone administration. However, the testosterone‐increased courtship displays of males did not increase female receptivity or serum LH, or stimulate reproductive development or egg‐laying in unpaired females placed with them. Females confined in cubicles within a pen that held breeding pairs and a free‐swimming flock had higher serum LH levels and laid more eggs than did females in cubicles in another pen without breeding pairs or a free‐swimming flock. This suggests that social factors, such as vocalizations from a flock and breeding pairs, may increase serum LH and egg‐laying in unpaired females. Oestradiol implants in female Canvasbacks did not elevate receptivity to courting drakes, nor did they stimulate pair formation, nesting activity, or egg‐laying behaviour. Testosterone implants in drakes and oestradiol implants in females decreased serum LH in each group. These results show that increasing the amount of courtship is not adequate to stimulate pairing behaviour or increases in reproductive hormones. Thus, our results suggest that female receptivity to male courtship may be a key determinant of pair formation and consequent synchronization of the behaviour patterns between members of a pair of wild birds. Our results may further suggest a dissociation between effects of courtship and pair formation in wild Canvasbacks.