Robert L. Jarvis

Survival of Mallard Broods in South-Central North Dakota

-Survival characteristics of 25 broods of Mallards (Anas platyrhynchos) were determined on a study area in the Missouri Coteau of south-central North Dakota in 1976-1977. Radio-equipped Mallard hens fledged at least one duckling in 7 of 16 (44%) broods produced in 1976, 5 of 9 (55%) in 1977, and 12 of 25 (48%) for both years combined. Of the 13 broods in which all young were lost, 11 (85%) were lost within the first two weeks after hatching. All losses of entire broods occurred in wetlands; few ducklings and no entire broods were lost during overland travel. Predation by mink (Mustela vison) was apparently the principal cause of duckling mortality. The magnitude and pattern of brood mortality are key factors in the reproductive ecology of waterfowl. Measurement of brood survival is essential for calculating recruitment from nesting data (Cowardin and Johnson 1979). Yet, survival and mortality patterns during the prefledging period are poorly understood. Most duckling mortality in Mallards (Anas platyrhynchos) occurs before young are three weeks old (Dzubin and Gollop 1972, Ball et al. 1975), but the specific mortality factors of ducklings are largely unknown. Predation, accidents, and losses due to scattering or exhaustion are often cited as potential agents of mortality, but little direct evidence has been presented in the literature. Some workers have suggested that overland travel is particularly hazardous to survival of ducklings (Bellrose 1953, Keith 1961, Odum 1970, Dzubin and Gollop 1972). However, Evans and Black (1956) found no evidence that mobile broods suffered more mortality than sedentary broods in prairie wetland habitat. This paper describes survival characteristics of Mallard broods on a study area in southcentral North Dakota as determined by radio telemetry and observation. To identify factors contributing to duckling mortality, we studied the effects of overland movement, predation, and hen-brood bonds on the survival of Mal-

Winter survival of adult female harlequin ducks in relation to history of contamination by the Exxon Valdez oil spill

Harlequin duck (Histrionicus histrionicus) life-history characteristics make their populations particularly vulnerable to perturbations during nonbreeding periods. The 1989 Exxon Valdez oil spill was a major perturbation to nonbreeding habitats of harlequin ducks in Prince William Sound, Alaska, which resulted in population injury. To assess the status of population recovery from the oil spill and to evaluate factors potentially constraining full recovery, we used radiotelemetry to examine survival of adult female harlequin ducks during winters of 1995-96, 1996-97, and 1997-98. We implanted 294 harlequin ducks (154 and 140 in oiled and unoiled areas, respectively) with transmitters and tracked their signals from aircraft during October through March. We examined variation in survival rates relative to area and season (early, mid, and late winter) through comparisons of models using Akaikes information criterion (AIC c ) values. The 3 models best supported by the data indicated that survival of birds in oiled areas was lower than in unoiled areas. Inclusion of standardized body mass during wing molt in the 3 best models did not improve their fit, indicating that body mass during wing molt did not affect subsequent winter survival. In the model that best fit our data, survival was high in early winter for both areas, lower during mid and late winter seasons, and lowest in oiled areas during mid winter. Cumulative winter survival estimated from this model was 78.0% (SE = 3.3%) in oiled areas and 83.7% (SE = 2.9%) in unoiled areas. We determined that area differences in survival were more likely related to oiling history than intrinsic geographic differences. Based on a demographic model, area differences in survival offer a likely mechanism for observed declines in populations on oiled areas. Concurrent studies indicated that harlequin ducks continued to be exposed to residual Exxon Valdez oil as much as 9 years after the spill. We suggest that oil exposure, mortality, and population dynamics were linked and conclude that continued effects of the oil spill likely restricted recovery of harlequin duck populations through at least 1998.

Survival of radio-marked mallard ducklings in Northeastern California

Estimates of duckling survival are necessary to accurately assess recruitment of mallards (Anas platyrhynchos), yet few reliable estimates exist. During 1988-90, we estimated survival rates for 127 radio-marked mallard ducklings from 64 broods on Lower Klamath National Wildlife Refuge, California. In 1988, we restricted the survival estimate to the first 10 days post-hatch (S = 0.18, SE = 0.07). Survival from hatching to 50 days was 0.37 (SE = 0.09) in 1989 and 0.34 (SE = 0.07) in 1990. Total brood loss differed among years (P < 0.05); 81.2% in 1988 (n = 16), 36.8% in 1989 (n = 19), and 37.5% in 1990 (n = 24). Ninety-three percent of mortality occurred during the first 10 days of life. We detected no differences in the proportion of radio-marked ducklings fledged from early-hatched versus late-hatched nests (P = 0.74)

The energetics of migration and reproduction of Dusky Canada Geese

We analyzed the carcass composition of 160 adult female Dusky Canada Geese (Branta canadensis occidentalis) collected in Oregon and Alaska from 1977 to 1979, to determine energy use patterns from premigration to hatch. We tested the predictions that geese would accumulate nergy reserves during migration, experience a gradual oss during prelaying and a severe loss during laying and incubation. Energy requirements met from food were estimated by comparing changes in endogenous reserves to estimated daily energy requirements. Body mass, and water, lipid and protein components varied by stage of reproduction (P = 0.000 l), and protein also varied by year (P = 0.0001). The brief migration period was costly, with a 52% decline in lipids, indicating that strategies to meet these energy demands are pivotal and will influence subsequent energy dynamics of reproduction. Geese maintained or increased lipid and protein reserves during the prelaying period, gradually lost reserves during laying and experienced considerable declines during incubation. Use of food for energy and nutrient requirements was important at all stages, accounting for 24% during incubation, the smallest but perhaps most critical contribution, to 100% during prelaying, of estimate daily energy requirements. The contribution of exogenous (food), versus endogenous sources, to energy and nutrient requirements of northern nesting geese is proving to be much more important than previously thought.

Feeding ecology of waterfowl wintering on evaporation ponds in California

We examined the feeding ecology of Northern Pintails (Anas acuta), Northern Shovelers (A. clypeata), and Ruddy Ducks (Oxyura jamaicensis) wintering on drainwater evaporation ponds in California from 1982 through 1984. Pintails primarily consumed midges (Chironomidae) (39.3%) and widegeongrass (Ruppia maritima) nutlets (34.6%). Shovelers and Ruddy Ducks consumed 92.5% and 90.1% animal matter, respectively. Water boatmen (Corixidae) (51.6%), rotifers (Rotatoria) (20.4%), and copepods (Copepoda) (15.2%) were the most important Shoveler foods, and midges (49.7%) and water boatmen (36.0%) were the most important foods of Ruddy Ducks. All three species were opportunistic foragers, shifting their diets seasonally to the most abundant foods given their behavioral and morphological attributes.

Testing assumptions for unbiased estimation of survival of radiomarked harlequin ducks

Unbiased estimates of survival based on individuals outfitted with radiotransmitters require meeting the assumptions that radios do not affect survival, and animals for which the radio signal is lost have the same survival probability as those for which fate is known. In most survival studies, researchers have made these assumptions without testing their validity. We tested these assumptions by comparing interannual recapture rates (and, by inference, survival) between radioed and unradioed adult female harlequin ducks (Histrionicus histrionicus), and for radioed females, between right-censored birds (i.e., those for which the radio signal was lost during the telemetry monitoring period) and birds with known fates. We found that recapture rates of birds equipped with implanted radiotransmitters (21.6 + 3.0%; i +SE) were similar to unradioed birds (21.7 ? 8.6%), suggesting that radios did not affect survival. Recapture rates also were similar between right-censored (20.6 ? 5.1%) and known-fate individuals (22.1 ? 3.8%), suggesting that missing birds were not subject to differential mortality. We also determined that capture and handling resulted in short-term loss of body mass for both radioed and unradioed females and that this effect was more pronounced for radioed birds (the difference between groups was 15.4 ? 7.1 g). However, no difference existed in body mass after recapture 1 year later. Our study suggests that implanted radios are an unbiased method for estimating survival of harlequin ducks and likely other species under similar circumstances. JOURNAL OF WILDLIFE MANAGEMENT 64(2):591-598

Movements and habitat use of mallard broods in northeastern California

To increase recruitment of mallards (Anas platyrhynchos), wildlife managers must understand the habitat and space needs of mallard broods. During 1989-90, we examined the movements, home range, and habitat use of 27 radio-marked mallard broods on Lower Klamath National Wildlife Refuge, California. Twelve of the 27 broods made 22 relocation movements (>1,000 m in 24 hr) in the first week (n = 6) and after the fourth (n = 16) week of life. Mean home range size was 0.93 km 2 (SE = 0.25) and did not differ between years (P = 0.26). Brood-rearing females selected seasonally flooded wetlands with a cover component and avoided open or permanently flooded habitats

Distribution and movements of female northern pintails radiotagged in San Joaquin Valley, California

To improve understanding of northern pintail (Anas acuta) distribution in central California (CCA), we radiotagged 191 Hatch-Year (HY) and 228 After-Hatch-Year (AHY) female northern pintails during late August-early October, 1991-1993, in the San Joaquin Valley (SJV) and studied their movements through March each year. Nearly all (94.3%) wintered in CCA, but 5.7% went to southern California, Mexico, or unknown areas; all that went south left before hunting season. Of the 395 radiotagged pintails that wintered in CCA, 83% flew from the SJV north to other CCA areas (i.e., Sacramento Valley [SACV], Sacramento-San Joaquin River Delta [Delta], Suisun Marsh, San Francisco Bay) during September-January; most went during December. Movements coincided with start of hunting seasons and were related to pintail age, mass, capture location, study year, and weather. Among pintails with less than average mass, AHY individuals tended to leave the SJV earlier than HY individuals. Weekly distribution was similar among capture locations and years but a greater percentage of pintails radiotagged in Tulare Basin (south part of SJV) were known to have (10.3% vs. 0.9%) or probably (13.8% vs. 4.6%) wintered south of CCA than pintails radiotagged in northern SJV areas (i.e., Grassland Ecological Area [EA] and Mendota Wildlife Area [WA]). Also, a greater percentage of SJV pintails went to other CCA areas before hunting season in the drought year of 1991-1992 than later years (10% vs. 3-5%). The percent of radiotagged pintails from Grassland EA known to have gone south of CCA also was greater during 1991-1992 than later years (2% vs. 0%), but both the known (19% vs. 4%) and probable (23% vs. 12%) percent from Tulare Basin that went south was greatest during 1993-1994, when availability of flooded fields there was lowest. The probability of pintails leaving the SJV was 57% (95% CI = 8-127%) greater on days with than without rain, and more movements per bird out of SJV occurred in years with more rain and fog but fewer days with southerly winds. Movements by pintails and changes in pintail distributions, direct recovery distributions, and harvest rates suggest the disproportionate decline of pintails in Tulare Basin was due to a lower percentage of pintails moving there in fall and a greater percentage or earlier movements north and south out of Tulare Basin. With fewer in Tulare Basin to replace Grasslands EA pintails going north in December, pintail abundance in the northern SJV declined during late winter. Changes in movement patterns correspond to habitat loss in Tulare Basin and increased habitats in SACV and western mainland Mexico. Habitat improvements, especially in Tulare Basin, that increase food, sanctuary, and winter survival would probably help restore pintails throughout the SJV.

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

September-March survival of female northern pintails radiotagged in San Joaquin Valley, California

To improve understanding of pintail ecology, we radiotagged 191 hatch-year (HY) and 228 after-hatch-year (AHY) female northern pintails (Anas acuta) in the San Joaquin 7 Valley (SJV), and studied their survival throughout central California, USA, during September-March, 1991-1994. We used adjusted Akaike Information Criterion (AIC c ) values to contrast known-fate models and examine variation in survival rates relative to year, interval, wintering region (SJV, other central California), pintail age, body mass at capture, capture date, capture area, and radio type. The best-fitting model included only interval x year and age x body mass; the next 2 best-fitting models also included wintering region and capture date. Hunting caused 83% of the mortalities we observed, and survival was consistently lower during hunting than nonhunting intervals. Nonhunting and hunting mortality during early winter was highest during the 1991-1992 drought year. Early-winter survival improved during the study along with habitat conditions in the Grassland Ecological Area (EA), where most radiotagged pintails spent early winter. Survival was more closely related to body mass at capture for HY than AHY pintails, even after accounting for the later arrival (based on capture date) of HY pintails, suggesting HY pintails are less adept at improving their condition. Thus, productivity estimates based on harvest age ratios may be biased if relative vulnerability of HY and AHY pintails is assumed to be constant because fall body condition of pintails may vary greatly among years. Cumulative winter survival was 75.6% (95% CI = 68.3% to 81.7%) for AHY and 65.4% (56.7% to 73.1%) for HY female pintails. Daily odds of survival in the cotton-agriculture landscape of the SJV were -21.3% (-40.3% to +3.7%) lower than in the rice-agriculture landscape of the Sacramento Valley (SACV) and other central California areas. Higher hunting mortality may be 1 reason pintails have declined more in SJV than in SACV.