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USGS1994

Breeding patterns and reproductive success of California sea otters

Following commercial exploitation in the eighteenth and nineteenth centuries, sea otter ( Enhydra lutris ) populations in Alaska, British Columbia, and Washington recovered at 17-20% a year, yet the California population increased at only 5% a year. This slow rate of increase is perplexing, given that unoccupied and apparently favorable habitats occur throughout the sea otter's California range, and higher growth rates occurred among northern sea otter populations. Better knowledge of the demography of the California population is important in understanding these disparate population growth rates. We studied the reproductive biology and behavior of 53 tagged female sea otters from 1985 to 1991 in Monterey Bay, California. During the study, 136 pups were born to these females. Observations of each female enabled us to determine exact or estimated pup birth dates, which we used to calculate lengths of gestation, pup dependency, and reproductive cycle. Seasonal trends in pupping, in the proportion of adult females with pups, and in pup separations from their mothers were relatively uniform throughout the year. The average interval between separation from pup and subsequent birth was 198 days, the interbirth interval was 407 days, and estimated birth rate was 0.90/year for all adult females. For females that pupped annually (did not lose undetected newborns), the average interbirth interval was 342 days, given an estimated birth rate of 1.07/year. Length of the reproductive cycle increased with increasing length of prior pup dependency. However, the interval between separation from pup and subsequent birth was delayed among females that prematurely lost their pups. The average length of dependency for pups that survived to weaning was 166 days, but ranged from 120 to 280 days. The maximum preweaning survival rate was 0.60-0.65, less than values measured or inferred for some Alaskan populations. Most pups that did not survive to weaning were lost within a month of birth. The probability of successfully weaning pups and the length of dependency increased ( P = 0.077) with mothers' ages, thus indicating that reproductive success may increase among females with greater mothering experience. The high preweaning pup mortality we observed probably accounts for much of the relatively slow growth rate of the California sea otter population.

California↗
USGS1994

An alternative index of satellite telemetry location error

Existing indices of satellite telemetry error offer objective standards for censoring poor locations, but have drawbacks. Examining distances and relative directions between consecutive satellite telemetry locations, I developed an alternative error index, ξ, and compared its performance with that of the location quality index, NQ (Serv. Argos 1988). In controlled tests, ξ was more (P ≤ 0.005) effective for improving precision than was a threshold of NQ > 1. The ξ index also conferred greater control over the trade off between sample size and precision, making ξ more cost-effective than NQ. Performances of ξ and NQ were otherwise comparable. In field tests with bighorn sheep ( Ovis canadensis ), rejecting locations where ξ ≥ 1.5 km reduced (P < 0.001) longitudinal dispersion, the predominant error component. Longitudinal dispersion for these locations was less (P = 0.025) than for locations where NQ > 1 and 63% fewer data were censored, so that the extent of animals' movements was better indicated by using ξ rather than NQ. Because use of ξ may lead to underestimating the number of long-range, short-term forays (especially when the frequency of forays is high relative to sampling frequency), potential bias should be considered before using ξ. Nonetheless, ξ should be a useful alternative to NQ in many animal-tracking studies.

Journal of Wildlife Management↗
USGS1994

Tundra swan habitat preferences during migration in North Dakota

I studied tundra swan (Cygnus columbianus columbianus) habitat preference in North Dakota during autumn migration, 1988-89. Many thousand tundra swans stop in the Prairie Pothole region during autumn migration, but swan resource use has not been quantified. I examined habitat preference in relation to an index of sago pondweed ( Potamogeton pectinatus ) presence, extent of open water, and wetland size. I compared habitat preference derived from counts of all swans to those derived from foraging swans only and cygnets only. Foraging swans preferred wetlands with sago pondweed ( P = 0.03); the number of foraging swans per wetland was >4 times higher on wetlands with sago pondweed than on wetlands without sago. In contrast, nonforaging swans did not prefer wetlands with sago pondweed ( P = 0.85) but preferred large wetlands ( P = 0.02) and those with a high proportion of contiguous open water ( P < 0.01). Thus, conclusions about habitat preference derived from counts of all swans, most of which were nonforaging, would not have revealed the importance of sago pondweed. Cygnets were more likely to be feeding than adults ( P = 0.03) and occurred proportionately more often in smaller flocks ( P = 0.04), but cygnets and adults had similar habitat preferences.

North Dakota↗
USGS1990

Effects of winter undernutrition on body composition and physiological profiles of white-tailed deer

We examined the effects of undernutrition and recovery on body composition and blood and urinary profiles of 6 captive white-tailed deer ( Odocoileus virginianus ) between 18 December 1984 and 3 May 1985. Deer were weighed, and blood and urine were collected every 2 weeks from 10 January to 3 May. At Weeks 2, 8, and 14, body composition was estimated by the dilution of tritiated water technique and standard predictive equations. Feed intake decreased and cumulative mass loss increased during nutritional restriction. Baseline body composition included 62.1 ± 0.9 (SE)% water, 11.9 ± 1.0% fat, 20.5 ± 0.7% protein, and 4.5 ± 0.0% ash. Percent protein loss was linearly related (r 2 = 0.91, P < 0.001) to percent mass loss. Peak mass loss from the beginning of the study (12.8 ± 2.0%) occurred at Week 12; estimated protein loss was 12.5%. Fat reserves were 85% depleted from Week 2 to Week 14. Elevated packed cell volume (PCV), serum calcium (Ca), cholesterol, triglycerides, and cortisol; and diminished serum urea nitrogen, thyroxine (T4), urinary urea nitrogen: creatinine and potassium: creatinine were associated with reduced food intake, mass loss, and decreases in body water, fat, and protein. Altered values of most of these blood and urinary characteristics reflected initiation of nutritional recovery after nutrition improved. Sequential data collection and the use of a combination of indices in blood or urine will yield the most useful assessments of animal nutrition and condition.

Minnesota↗
USGS1990

Neck-band retention for Canada geese in the Mississippi flyway

We used capture, harvest, and observation histories of Canada geese ( Branta canadensis ) banded in the Mississippi flyway, 1974-88, to examine the problem of neck-band retention. Methods for the analysis of survival data were used to estimate rates of neck-band retention and to evaluate factors associated with neck-band loss. Sex, age of bird at banding, rivet use, and neck-band type significantly influenced neck-band retention. For most of the resulting cohorts (e.g., sex, age, rivet, and neck-band type categories), neck-band retention rates decreased through time. We caution against using small samples or data collected during short-term studies to determine retention rates. We suggest that observation data be used in neck-band retention studies to increase the efficiency of estimating retention time.

Journal of Wildlife Management↗
USGS1990

Survival and band recovery rates of mallards in New Zealand

Mallards ( Anas platyrhynchos ) were banded at 4 discrete study areas in New Zealand. We used hunting season recoveries in conjunction with band recovery models to estimate annual survival and recovery rates and to test hypotheses about sources of variation in these rates. Recovery rates varied among the 4 areas and from year to year within areas. Recovery rates were generally higher for young mallards than for adults, and recovery rates of males were higher than those of females. Survival rates varied among the 4 areas and from year to year within some areas. Survival rates of females were lower than those of males, but survival rates of young birds were not consistently lower than those of adults. Average survival rates over all 4 areas were generally lower than averages for North American mallards.

Journal of Wildlife Management↗
USGS1994

Anticholinesterase exposure of white-winged doves breeding in lower Rio Grande valley, Texas

We studied exposure of breeding white-winged doves (Zenaida asiatica) to anticholinesterase compounds (organophosphorus and carbamate pesticides) in the Lower Rio Grande Valley (LRGV), Texas. Widespread use of organophosphorus pesticides and dove population declines prompted the study. We collected breeding adult doves in May and July 1991 (n = 28) and July 1992 (n = 33) at 6 locations. We used depression of whole-brain cholinesterase (ChE) activity (2 SD below control mean) to detect exposure; values from 4 hand-reared doves fed commercial pigeon chow served as the control. Mean brain ChE activity was lower (P lt 0.027) than the control sample at all 6 locations in 1991; 79% of the birds were diagnostic of exposure ( gt 16.1% ChE depression). Pooled 1992 field samples also were lower (P lt 0.036) than were control samples; doves from 4 of the 6 locations had brain ChE activity below (P lt 0.088) controls. Overall, 39% of 1992 doves were diagnostic of exposure to anticholinesterase compounds. Higher exposure rates in 1991 were probably due to increased use of organophosphorus pesticides. Research is needed documenting effects of sublethal exposure on white-winged dove productivity.

Texas↗
USGS1994

Estimates of soil ingestion by wildlife

Many wildlife species ingest soil while feeding, but ingestion rates are known for only a few species. Knowing ingestion rates may be important for studies of environmental contaminants. Wildlife may ingest soil deliberately, or incidentally, when they ingest soil-laden forage or animals that contain soil. We fed white-footed mice ( Peromyscus leucopus ) diets containing 0-15% soil to relate the dietary soil content to the acid-insoluble ash content of scat collected from the mice. The relation was described by an equation that required estimates of the percent acid-insoluble ash content of the diet, digestibility of the diet, and mineral content of soil. We collected scat from 28 wildlife species by capturing animals, searching appropriate habitats for scat, or removing material from the intestines of animals collected for other purposes. We measured the acid-insoluble ash content of the scat and estimated the soil content of the diets by using the soil-ingestion equation. Soil ingestion estimates should be considered only approximate because they depend on estimated rather than measured digestibility values and because animals collected from local populations at one time of the year may not represent the species as a whole. Sandpipers ( Calidris spp.), which probe or peck for invertebrates in mud or shallow water, consumed sediments at a rate of 7-30% of their diets. Nine-banded armadillo ( Dasypus novemcinctus , soil = 17% of diet), American woodcock ( Scolopax minor , 10%), and raccoon ( Procyon lotor , 9%) had high rates of soil ingestion, presumably because they ate soil organisms. Bison ( Bison bison , 7%), black-tailed prairie dog ( Cynomys ludovicianus , 8%), and Canada geese ( Branta canadensis , 8%) consumed soil at the highest rates among the herbivores studied, and various browsers studied consumed little soil. Box turtle ( Terrapene carolina , 4%), opossum ( Didelphis virginiana , 5%), red fox ( Vulpes vulpes , 3%), and wild turkey ( Meleagris gallopavo , 9%) consumed soil at intermediate rates. Ingested soil may be the principal means of exposure to some environmental contaminants or the principal source of certain minerals. Soil-ingestion estimates may be required for risk assessments of wildlife inhabiting contaminated sites and for computing budgets of those nutrients associated mainly with soil.

Colorado, Kansas, Louisiana, Maine, Maryland, Minn↗
USGS1993

Factors influencing depredation of artificial duck nests

Because artificial nests can facilitate controlled experiments of nest success, we used them to assess whether human visitation, nest density, vegetation structure, and proximity to habitat edge could affect depredation of duck nests on Yukon Flats National Wildlife Refuge, Alaska. More (P < 0.01) nests in a plot visited daily (100%) were depredated than those in plots visited at intervals of 7 (40%), 14 (35%), or 28 days (45%). More (P < 0.01) nests were depredated in a plot with 10 nests/ha (95%) than nests in a plot of a lower density (2/ha; 40%). Vegetation height, vegetation density, distance to a wetland, distance to forest edge, or distance to the nearest ecotone did not differ (P > 0.05) between depredated and undisturbed nests. We suggest that daily visitation of duck nests increases depredation, but longer intervals, typical of most nest studies, do not. High nesting densities, which could occur when flooding limits nesting habitat, may result in higher depredation rates.

Alaska↗
USGS1991

Energy dynamics, foraging ecology, and behavior of prenesting greater white-fronted geese

We collected greater white-fronted geese (Anser albifrons frontalis) on their nesting grounds on the Yukon-Kuskokwim Delta, Alaska, when they arrived and again before incubation during 1986 and 1987. Body mass, water content, crude fat, and crude protein increased in female geese between arrival and incubation onset in 1986 and 1987 (P = 0.0001, 0.0002, 0.0329, and 0.0003, respectively). Body mass of male geese during prenesting did not change, but total fat content decreased by about 30%. Crude protein of males was different between years (P = 0.0014). Female geese spent more time feeding than did males (P < 0.001). Primary foods during the prenesting period were pendent grass (Arctophila fulva) shoots and arrowgrass (Triglochin palustris) bulbs. Gizzard contents and orifice staining indicated crowberries (Empetrum nigrum) also were consumed. Of the commonly consumed food items, arrowgrass bulbs had the greatest protein content (21%), and crowberries had the greatest lipid content (10%). Unlike other medium-sized, northern-nesting geese, food (energy) acquired on the nesting grounds by white-fronted geese before incubation increased endogenous reserves necessary for reproduction.

Journal of Wildlife Management↗
USGS1991

Survival of postfledging female American black ducks

We equipped 106 hatching-year (HY), female, black ducks ( Anas rubripes ) with transmitters during 1985-87 and monitored survival from late August to mid-December on a lightly hunted area on the Maine-New Brunswick border. The 1985-87 estimate of survival (hunting losses included) was 0.593, and when losses from hunting were censored it was 0.694. Survival in August-September was 0.987; by 31 October survival declined to 0.885, and by 30 November it was 0.718. Most nonhunting mortality was caused by predators (21/41, 53.2%); there were 14 deaths (34.1%) from mammals or unknown predators and 7 (17.1%) from raptors. Hunting caused 13 (31. 7%) deaths. Ducks with lowest mass had the lowest survival. The estimate of survival for postfledging female black ducks, when multiplied with interval survival rates for hunting, winter, and breeding periods, produced an annual survival estimate of 0.262, about 12% lower than that (0.38) based on analysis of banding data.

Maine↗
USGS1994

Polar bear maternity denning in the Beaufort Sea

The distribution of polar bears ( Ursus maritimus ) is circumpolar in the Northern Hemisphere, but known locations of maternal dens are concentrated in relatively few, widely scattered locations. Denning is either uncommon or unknown within gaps. To understand effects of industrial development and propose increases in hunting, the temporal and spatial distribution of denning in the Beaufort Sea must be known. We caputred and radiocollared polar bears between 1981 and 1991 and determined tht denning in the Beaufort Sea region was sufficient to account for the estimated population there. Of 90 dens, 48 were on drifting pack ice, 38 on land, and 4 on land-fast ice. The portions of dens on land was higher ( P = 0.029) in later compared with earlier years of the study. Bears denning on pack ice drifting as far as 997 km ( x = 385 km) while in dens. there was no difference in cub production by bears denning on land and pack ice ( P = 0.66). Mean entry and exit dates were 11 November and 5 April for land dens and 22 November and 26 March for pack-ice dens. Female polar bears captured in the Beaufort Sea appeared to be isolated from those caught east of Cape Bathurst in Canada. Of 35 polar bears that denned along the mainland coast of Alaska and Canada 80% denned between 137°00′W and 146°59′W . Bears followed to >1 den did not reuse sites and consecutive dens were 20-1,304 km apart. However radio-collared bears are largely faithful to substrate (pack-ice, land, and land-fast ice) and the general geographic area of previous dens. Bears denning on land may be vunerable to human activities such as hunting and industrial development. However, predictable denning chronology and lack of site fidelity indicate that many potential impacts on denning polar bears could be mitigated.

Alaska↗
USGS1994

Retention of web tags and plasticine-filled leg bands applied to day-old ducklings

A new plasticine-filled leg band was developed for use in banding dayold ducklings. These bands permit inference about early survival that is not possible from banding of older young in standard operations. Two double-marking experiments with web tags and the new leg bands indicated a high retention rate for the leg bands. In contrast, several web tags were lost, permitting an analysis directed at sources of variation in web tag retention rates. We found retention rates of web tags to be higher for diving ducks ( Aythya ) than for dabbling ducks ( Anas ), and higher for tags placed the web interior than for those applied to the web edge. However, we recommend that the new plasticine-filled leg bands be used in place of web tags because of their higher retention rates and presumably greater visibility to hunters. We believe they offer great potential for new studies of duckling survival and distribution.

Engure Marsh↗
USGS1994

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). During 1989-90, 16 females appeared to lose their entire brood; however, 3 radio-marked ducklings from 2 of these broods were fledged by other brood hens. Of 29 radio-marked ducklings that reached 44 days of life, 6 (20.7%) joined other broods. Habitat enhancement is the key to improving duckling survival because the large number of predator species that consume ducklings makes predator control difficult.

California↗
USGS1994

Dioxins and furans linked to reproductive impairment in wood ducks

A wetland in central Arkansas was contaminated with polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans and because the area was a major waterfowl habitat, we studied the effects of the contamination on nesting wood ducks ( Aix sponsa ) during 1988-90. Residues in wood duck eggs, based on toxicity equivalency factors (TEFs) for combined compounds, ranged from 0.2 to 611 parts per trillion (ppt) wet mass (70% were the toxic isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (tetraCDD)) and were 50 times higher in eggs from near the point source than from an uncontaminated reference site 111 km away. Nest success, hatching success, and duckling production were suppressed ( P < 0.05) at nesting sites 9 and 17 km downstream, as was hatching success 58 km downstream. Egg TEFs were inversely correlated ( P < 0.001) with productivity in corresponding nests. In addition, teratogenic effects occurred in ducklings at the more contaminated nesting site nearest the point source. The threshold range of toxicity (based on TEFs) where reduced productivity was evident in wood ducks was gt 20-50 ppt. Wood ducks were sensitive to dioxin and furan contamination, and we recommend it as an indicator species for monitoring biological impacts from these contaminants.

Arkansas↗
USGS1994

Herbivory on shoalgrass by wintering redheads in Texas

An estimated 80% of redheads ( Aythya americana ) winter on the Laguna Madre of south Texas and Mexico and feed almost exclusively on shoalgrass ( Halodule wrightii ) rhizomes. Shoalgrass abundance has decreased by 60% over the past 30 years, and because the effects of shoalgrass loss on wintering redheads are unknown, we initiated a study to define habitat selection criteria and document the effect of wintering redheads on shoalgrass in the lower Laguna Madre, Texas. Redheads consumed an average of 75% of shoalgrass rhizome biomass at collection sites each winter. When rhizome biomass was grazed to a mean biomass of ltoreq 0.18 g dry mass/core (approximately 10 g dry mass/ml), shoalgrass did not recover to its previous level the following growing season. Thirty-three percent of the sites (10) were grazed below 0.18 g dry mass/core during both years of the study, while 64% (19) were grazed below 0.18 g during 1 or the other of the 2 winters. Ramet number was positively correlated ( P < 0.001, r 2 = 0.54) with rhizome biomass; however, this relationship was influenced by grazing intensity. Heavy grazing reduced the amount of rhizome attached to each ramet compared with ungrazed ramets. Grazing had no effect on root biomass ( P = 0.388), rhizome moisture content ( P = 0.553), or soil magnesium, phosphorous, and potassium ( P = 0.102, 0.499, 0.162, respectively). Redhead presence increased ( P = 0.042) soil nitrogen levels. Foraging areas selected by redheads within the lower Laguna Madre had lower ( P = 0.026) salinities (24 ppt) than areas not selected (35 ppt). Redheads did not select foraging areas in relation to crude protein levels in rhizomes. Shoalgrass habitat in the Laguna Madre should be protected from further losses and enhanced where possible.

Texas↗
USGS1994

Survival rates of American woodcock wintering along the Atlantic coast

Because American woodcock ( Scolopax minor ) populations have been declining, we attached radio transmitters to woodcock at coastal plain sites to determine if survival during winter was involved in the decline. Sites were in Georgia (1982-84, 1989-92), South Carolina (1988-89), and Virginia (1991-92). Survival rates were not different between age or sex classes. Survival rates differed ( P = 0.003) among years. Daily survival rates were lowest ( P = 0.030, S = 0.987) during 1982-83 in Georgia and highest ( P = 0.004, S = 0.999) during 1990-91 in Georgia than in the other years and locations combined ( S = 0.996). We attributed all mortality to raptors and mammals. Compared with other periods of the year, winter was a time of low survival for woodcock. Lower survival rates were possibly a cause of population decline.

Georgia, South Carolina, Virginia↗
USGS1994

Essential amino acids in northern bobwhite foods

Frequent population declines, high dietary requirements for protein, and the low quality of proteins in agricultural grains led us to hypothesize that essential amino acid (EAA) deficiencies were common in northern bobwhite (Colinus virginianus) foods. We analyzed amino acid concentrations of 21 northern bobwhite foods and compared them with dietary requirements to derive values that reflected the foods' ability to meet daily bobwhite requirements of 10 EEAs. Despite adequate concentrations of crude protein, deficiencies of EAAs were detected in seeds of all species analyzed. Legumes offered the best mix of EAA, and grasses the poorest. Deficiencies of EEAs relative to maintenance requirements of adults ranged from 13% in legumes to 98% in grasses. About a third of the total nitrogen pool was composed of nonprotein nitrogen with values ranging from 25% for queensdelight stillingia (Stillingia sylvatica) to 44% for redroot amaranth (Amaranthus retroflexus). Computed biological values (ratio of EEA concentrations in seed protein to respective amounts in whole egg protein) ranged from 69 (netleaf hackberry [Celtis reticulata]) to 93 (erect dayflower [Commelina erecta] and woolly croton [Croton capitatus]). Amino acid profiles indicate forage quality better than crude protein estimates.

Journal of Wildlife Management↗