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D.S. Gilmer

Publications and source records attributed to D.S. Gilmer.

At least 19 recordsLinked to original sources
USGS2000

Pepperweed: a growing threat to western wildlife habitat

Counts on photographs and visual estimates of the numbers of territorial gulls are usually reliable indicators of the number of gull nests, but single visual estimates are not adequate to measure the number of nests in individual colonies. To properly interpret gull counts requires that several islands with known numbers of nests be photographed to establish the ratio of gulls to nests applicable for a given local census. Visual estimates are adequate to determine total breeding gull numbers by regions. Neither visual estimates nor photography will reliably detect annual changes of less than about 2.5 percent.

People, Land, and Water↗
USGS1997

Relationship between waterfowl nutrition and condition on agricultural drainwater ponds in the Tulare Basin, California: Waterfowl body composition

We examined carcass composition and proximate food composition of ruddy ducks ( Oxyura jamaicensis ), northern shovelers ( Anas clypeata ), and northern pintails ( Anas acuta ) wintering on agricultural drainwater ponds in California during 1983–84. Lipids varied seasonally in northern shovelers and northern pintails. Protein did not fluctuate except in ruddy ducks whose protein mass increased over winter, suggesting that some protein was catabolized prior to arrival on wintering areas or that a buildup of protein occurred prior to spring migration. Waterfowl diets varied among species and time, but the nutritional composition of the diets was relatively stable. Ruddy ducks and shovelers consumed mostly animal foods rich in protein (53–60%) and low in Nitrogen Free Extract (NFE) (1–7%). Pintail diets contained more NFE (23–38%) and less protein (14–38%) because of greater consumption of plant foods. Nutritional composition of pintail diets varied with lower protein consumption occurring from November through January.

California↗
USGS1991

Standing crops and ecology of aquatic invertebrates in agricultural drainwater ponds in California

We examined standing crops and ecology of aquatic invertebrates in agricultural drainwater evaporation ponds in California from October 1982 to March 1983 and September 1983 to March 1984. Evaporation ponds supported low diversities but high standing crops of aquatic invertebrates. A water boatman ( Trichocorixa reticulata ) and a midge ( Tanypus grodhausi ) were the most abundant invertebrates, constituting 44.9% and 51.4% of total macroinvertebrate biomass. Regression models indicated that of 6 environmental variables measured, only electrical conductivity (EC) and Julian date affected biomass and density of water boatmen. EC was the only significant correlate of midge biomass in evaporation ponds.

California↗
USGS1991

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.

Condor↗
USGS1989

Duck harvest on public hunting areas in California

We summarized hunter visits and success, and the magnitude and species composition of the duck harvest recorded on California public hunting areas (PHAs) during 1950-87. Hunter visits and harvest increased during 1950-74 as new PHAs were added, then declined concurrently with duck populations. Of six geographic regions, the Sacramento Valley, with numerous PHAs and the largest duck concentrations, accounted for the largest portion of PHA hunter visits (28%) and harvest (35%). Duck population levels, regulations, and hunter numbers affected PHA hunter success. Success was highest during 1955-59 but declined with no consistent trend after 1960. Species vulnerability, abundance, distribution, and hunter preference affected harvest composition. Northern pintails, Anas acuta, averaged 27% of the PHA harvest but declined in importance after 1974. Green-winged teal, A. crecca, the most important species in southern regions, averaged 21% of the PHA harvest. Mallards, A. platyrhynchos, averaged 16% of the PHA harvest but increased in importance after 1974 to become the most common duck bagged after 1983. PHA harvest comprised a small (4-16%) portion of the total state harvest. However, this portion increased from 1950-70 because of increased hunter visits to new PHAs and after 1970 because hunter success on PHAs did not decline as on other areas. PHA hunters tended to harvest fewer preferred species and more vulnerable species, as proportions of total bag, than did other hunters. The continued decline in numbers of waterfowl hunters presents important challenges for management of waterfowl areas in California.

California Fish and Game↗
USGS1988

Selenium levels in biota from irrigation drainwater impoundments in the San Joaquin Valley, California

Waterfowl, fish, invertebrates, and plants were collected from impoundments used for evaporating subsurface irrigation drainwater in Kings and Kern counties, California. Specimens were analyzed for trace elements with emphasis on selenium. Dry weight concentrations of total selenium ranged from 2.5 to 17 μg/g in wigeongrass, Ruppia maritima ; 7.6 to 30 μg/g in water boatmen, Corixidae ; 12 to 40 μ/g in mosquitofish, Gambusia affinis ; 86 to 100 μg/g in eared grebe, Podiceps niqricollis , livers; 14 to 120 μg/g in ruddy duck, Oxyura jamaicensis , livers; and 6.8 to 48 μg/g in northern shoveler, Anas clypeata , livers. Concentrations of dissolved selenium ranged from less than 1 to 37 μg/L during a 12-month period for inflows to the drainwater evaporation ponds.

Lake and Reservoir Management↗
USGS1984

Swainson's hawk nesting ecology in North Dakota

Swainson's Hawks (Buteo swainsoni) were studied at 270 occupied nest sites in south-central North Dakota on a 1,259-km2 intensive study block and on a surrounding study area (16,519 km2) during three breeding seasons. On the intensive study block the number of occupied nests ranged from 46 in 1977 to 100 in 1979. Average nest densities were highest on ground moraine (0.119 nest/km2) and on eolian sand deposit (0.102 nest/km2 landforms. Pasture and haylands made up 75% of the land-use within 1.0 km of a sample of 27 nests. Some pairs nested successfully in sites characterized by intensive agriculture and human activity; about 75% of all nests were in sites attributable to human activities. The most common nesting sites (43%) were in shelterbelts. Cottonwoods (Populus deltoides) were the most frequently used (44%) nest trees. At least 50% of the pairs constructed new nests each year. Mean nest success was 64% and mean number of young fledged per occupied nest was 1.5. Wind and hail caused over 30% of the nest failures each of the three years. Northern pocket gophers (Thomomys talpoides) were the most frequent prey, accounting for 44% of all animal remains found at nests. Man-made changes in central North Dakota during the last century have provided many nesting sites in areas previously sparsely populated by Swainson's Hawks.

North Dakota↗