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D.S. Gilmer

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

At least 37 records · Page 2Linked to original sources
USGS1989

Rice available to waterfowl in harvested fields in the Sacramento Valley, California

Rice fields in the Sacramento Valley, California were sampled in 1985 and 1986 to determine the weight of rice seed remaining in the fields immediately after harvest and again after the fields were burned. No significant differences were found between years (P>0.05). The pooled mean was 388 kg/ha in harvested fields and 276 kg/ha in burned fields. These values are less than estimates previously available. The values for harvested fields both years were no different (P>0.05) than values obtained by the U.S. Department of Agriculture (USDA). Surveys of rice fields in December both years showed that most fields were left either harvested (26-32%) or burned (37-40%) through the winter. Fields flooded for duck hunting made up 15% of the total. The proportion of fields plowed by December increased from 14% in 1985 to 22% in 1986. Sixty-three percent of all fields that had been flooded for hunting were drained within two weeks after the end of the hunting season. Harvest yield field size levee type (contour, lasered), straw status (spread, windrowed), harvest date, and rice variety did not affect the quantity of seeds remaining after harvest (P>0.05). One harvester model, the Hardy Harvester, left more rice in fields than did others we tested (P<0.001). Specific management programs are recommended to mitigate annual variation in rice seed availability to waterfowl caused by differences in total hectares grown (15% less in 1986) and in the proportion of fields burned and plowed.

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↗
USGS1986

Waterfowl harvest at Tule Lake National Wildlife Refuge, 1936-41

Waterfowl harvest at Tule Lake National Wildlife Refuge (NWR) for the 6-yr period 1936-41 is described and compared with a recent (1978-83) period. During the early period 46,987 geese and 76,143 ducks were bagged during 48,610 hunter-visits. Hunting seasons were 30 to 60 d in length. Greater White-fronted Geese Anser albifrons, followed by Northern Pintails Anas acuta, and Cackling Canada Geese Branta canadensis minima were the most important birds in the harvest. Average harvest was 1.0 goose and 1.6 ducks per hunter-visit. A short (30-d) and late hunting season drastically curtailed harvest in 1937. Reduced hunting activity in 1941 was attributed to military mobilization. During the 1978-83 period 34,416 geese and 63,458 ducks were bagged during 69,170 hunter-visits. Hunting seasons during this period were mostly 93 d in length. The most important bird in the harvest was the Mallard A. platyrhynchos, followed by White-fronted Goose and Northern Pintail. Average harvest was 0.5 goose and 0.9 duck per hunter-visit. In general dabbling ducks increased in overall importance while diving ducks decreased between the two periods. Harvest decreased 20.5% while hunter-visits increased 42.3%.

California Fish and Game↗
USGS1986

Post fledging behavior of ferruginous hawks in North Dakota

Post-fledging activities of 18 Ferruginous Hawks (Buteo regalis) were studied in southcentral North Dakota during July and August 1979. The post-fledging period ranged from 10 to 40 d (mean = 23.1 d; N = 16). Haylands and native prairie grasslands were the principal land use types utilized by fledglings and adults. Mortality of young during post-fledging was 11% (N = 2).

Journal of Raptor Research↗
USGS1985

Mallard recruitment in the agricultural environment of North Dakota

Recruitment of a mallard (Anas platyrhynchos) population was assessed on a 10,041-km2 study area in central North Dakota during 1977-80. We equipped 338 hens with radio transmitters and monitored them during the breeding season. Two hundred thirty-five of these hens furnished data reported here. Habitat use, nest site selection, fate of nests, and the rate of renesting were measured. Survival of hens during April-September and survival of young were determined. There was a high negative correlation between nest initiation date and mean April or May temperature. Hens selected nest sites most frequently in grassland and least frequently in cropland, but habitat use compared to availability indicated preference for road right-of-way and odd areas of cover and rejection of cropland. Use of other habitats was in proportion to their availability. Nest success was only 8% during the study. Hen success, a function of nest success and renesting rate, averaged 15% and varied among years because of increased renesting in wet years. In all years, 2-year-old and older hens were twice as successful as first-year nesters. Nesting effort was correlated with water conditions as derived from aerial photographs. April-September survival of hens averaged 80% because predation was heavy when hens were on nests. Only 74% of the hens that hatched a clutch were observed later with at least 1 surviving duckling. On average, hens in the spring population recruited only 0.27 young females to the fall population. Based on this recruitment estimate, published survival estimates and a model previously developed for a closed population, we predict a 20% annual population decline. Nest success of 15% and a resulting hen success of 31% would be required for a stable population. The results suggest that the population on the study area is not maintaining itself but is being supplemented by pioneering birds. A serious recruitment problem has resulted from nest predation. Additional research is needed to determine the geographic extent of the problem. If the problem is widespread, management techniques must be devised to overcome nest destruction, mortality of hens, and mortality of ducklings.

Wildlife Monographs↗
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↗
USGS1981

Characteristics of central North Dakota wetlands determined from sample aerial photographs and ground study

Wetland characteristics were assessed from a systematic sample of 66 plots, 3.22 km2 each, drawn from a 10,041-km2 study area in central North Dakota. Each plot was visited once and 8 sets of aerial photographs were obtained in 3 years. Density of wetland basins was 11.00 ha/km2, and area averaged 9.7 ha/km2. Seasonal and temporary wetlands were most abundant; semipermanent wetlands occupied the greatest area. Basin size was positively correlated with water permanence. Discriminant function analysis based on size and an index to wetness derived from photographs misclassified 33% of the wetland basins. Forty percent of the wetlands were tilled. Photography of sample plots is potentially useful for determining number of basins and wetland area, but precise classification of plant communities in this region would require ground study.

Wildlife Society Bulletin↗