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Geology topics

David E. Sharp

Publications and source records attributed to David E. Sharp.

8 recordsLinked to original sources
USGS2017

The migratory bird treaty and a century of waterfowl conservation

In the final decades of the nineteenth century, concern was building about the status of migratory bird populations in North America. In this literature review, we describe how that concern led to a landmark conservation agreement in 1916, between the United States and Great Britain (on behalf of Canada) to conserve migratory birds shared by Canada and the United States. Drawing on published literature and our personal experience, we describe how subsequent enabling acts in both countries gave rise to efforts to better estimate population sizes and distributions, assess harvest rates and demographic impacts, design and fund landscape-level habitat conservation initiatives, and organize necessary political and regulatory processes. Executing these steps required large-scale thinking, unprecedented regional and international cooperation, ingenuity, and a commitment to scientific rigor and adaptive management. We applaud the conservation efforts begun 100 years ago with the Migratory Bird Treaty Convention. The agreement helped build the field of wildlife ecology and conservation in the twentieth century but only partially prepares us for the ecological and social challenges ahead.

Journal of Wildlife Management↗
USGS1990

Weights of wild mallard Anas platyrhynchos, gadwall A. strepera, and blue-winged teal A. discors during the breeding season

During 1976-81 we weighed several thousands of wild Mallard, Gadwall, and Blue-winged Teal in central North Dakota to examine duckling growth patterns, adult weights, and the factors influencing them. One-day-old Mallard and Gadwall averaged 32.4 and 30.4 g, respectively, a reduction of 34% and 29% from fresh egg weights. In all three species, the logistic growth curve provided a good fit for duckling growth patterns. Except for the asymptote, there was no difference in growth curves between males and females of a species. Mallard and Gadwall ducklings were heavier in years when wetland area was extensive or had increased from the previous year. Weights of after-second-year females were greater than yearlings for Mallard but not for Gadwall or Blue-winged Teal. Adult Mallard females lost weight continuously from late March to early July. Gadwall and Blue-winged Teal females, which nest later than Mallard, gained weight after spring arrival, lost weight from the onset of nesting until early July, and then regained some weight. Females of all species captured on nests were lighter than those captured off nests at the same time. Male Mallard weights decreased from spring arrival until late May. Male Gadwall and Blue-winged Teal weights increased after spring arrival, then declined until early June. Males of all three species then gained weight until the end of June. Among adults, female Gadwall and male Mallard and Blue-winged Teal were heavier in years when wetland area had increased from the previous year; female Blue-winged Teal were heavier in years with more wetland area.

Wildfowl↗
USGS1990

Homing and reproductive habits of mallards, gadwalls, and blue-winged teal

We studied mallard ( Anas platyrhynchos ), gadwall ( A. strepera ), and blue-winged teal ( A. discors ) populations on 2 study areas of 22.6-km 2 each in central North Dakota during 1976-81. Data regarding rates of return of females to natal or previously used nesting areas, nest site selection, and productivity of hens of different ages were collected from 1,166 nasal-marked and 2,142 banded hens of the 3 species and from 740 web-tagged mallard and gadwall young. In spring, yearling mallard and gadwall hens arrived at the breeding site later than older hens. Yearling gadwall hens initiated nesting about 1 week later than 2-year-old hens, and 2-year-old hens began nesting about 1 week later than hens older than 2 years. Gadwall hens older than 2 years also had a longer nesting season. Mallard and gadwall nest densities were highest in those cover types with the highest visual obstruction ratings. Cover preference in descending order of use was seeded nesting cover, odd areas, roadside, dry wetland, and canal-side. Blue-winged teal nest densities were highest in dry wetland and roadside. Nesting success was different among years, but not among cover types. There was no population increase at any cover type due to homing hens. Overall nesting success was 11, 10, and 23% for mallards, gadwalls, and blue-winged teal, respectively. Recruitment of fledged young was similar for yearling and adult mallard females. Production from yearling gadwall hens was a meager 0.2 young fledged/female. Clutch size was not different between yearling and adult mallard and blue-winged teal hens, but clutch size for all 3 species declined as the nesting season advanced. More ≥1-year-mallard hens and ≥2-year-old gadwall hens that nested successfully 1 year returned to the study areas the following year than did unsuccessful hens. Gadwall hen return rates also increased with age. Blue-winged teal hen return rates averaged 4% and were not related to hen success or hen age. Mallard and gadwall hens that nested successfully 1 year used the same cover type the next year. Successful returning mallard hens also nested closer to the previous nest site than unsuccessful hens. Twenty-nine percent of hatching year (HY) mallard females returned to the study area, and all of these returned as yearlings (second summer). Nine percent of HY gadwalls returned, approximately half as yearlings and the remainder as 2 year olds. Duckling survival from hatching until near fledging was 0.681 for mallards and 0.828 for gadwalls. An overall direct band recovery rate of 8% for HY mallard hens was not different than that of older hens. Gadwall direct band recovery rates decreased through the HY (11%), yearling (5%), and >2-year (1%) age classes.

North Dakota↗
USGS1987

A decoy trap for breeding-season mallards in North Dakota

A modified decoy trap was effective for capturing wild adult male and female mallards ( Anas platyrhynchos ) during the 1980-81 breeding seasons in North Dakota. Key features contributing to the trap's success included a central decoy cylinder, large capture compartments with spring-door openings, an adjustable trigger mechanism with a balanced door attachment that was resistant to trap movement, and the use of F1, wild-stock or game-farm female decoys.

North Dakota↗
USGS1984

Nest spacing, habitat selection, and behavior of waterfowl on Miller Lake Island, North Dakota

The nesting behavior of a concentration of nesting mallards ( Anas platyrhynchos ) and gadwalls ( A. strepera ) was studied on a 4.5-ha island in Miller Lake, North Dakota, in 1977. A single 0.59-ha clump of thick shrub contained 225 simultaneously active mallard nests on 10 May. During the peak nesting period, mallard nests were spaced an average of 2.7 m from conspecifics. Active nests of all species peaked at 327, spaced an average of 2.1 m apart. Nests were clustered in thick shrub with moderate numbers in open shrub and few in grassland. Nest placement was significantly related to the amount of vegetative screening although mammalian predators were absent on the island. Cover density appeared to be important to the nesting hens as vegetation screened nests from potential avian predators and from harassment by other conspecific nesting hens and drakes. Mallards and gadwalls nesting on this island used wetlands in >100 km2 around Miller Lake. During daylight hours in late April 1978, an average of 4.9 mallards/minute arrived at the island; a peak of 17.2 mallards/minute arrived at 0800. In late April 1978, as many as 26 mallard pairs/ha occurred on favored wetlands and behavioral aggression was intense. Yet, most mallard hens maintained adequate space to acquire food and other requisites. Mallards and gadwalls were sufficiently adaptable to successfully exploit the Miller Lake island and environments that resulted in high reproductive success. Other local breeding Anatidae because of behavioral constraints were unable to exploit the same situation.

North Dakota↗
USGS1983

Concentrated nesting of mallards and gadwalls on Miller Lake Island, North Dakota

Island-nesting mallards ( Anas platyrhynchos ) and gadwalls ( A. strepera ) were studied on a 4.5-ha island in 385-ha Miller Lake in northwestern North Dakota during 1976-80. During the 5-year study, 2,561 duck nests of 9 species were found on Island A located 180 m offshore; 59% were mallard and 34% were gadwall. In patches of shrub cover, which contained the greatest concentrations of nests, densities ranged from 241 to 389 mallard nests/ha and from 139 to 237 gadwall nests/ha. Over 97% of the nests were placed in 4 patches of shrubs totaling about 1 ha of western snowberry ( Symphoricarpos occidentalis )--Woods rose ( Rosa woodsii ) cover, which composed about 30% of the island's vegetation. Average hatching success was 85% for clutches of all species. Abandonment averaged 14% (348 of 2,426 nests) and was the major cause of egg failure. Only 15 nests (<1%) were destroyed, primarily by ring-billed ( Larus delawarensis ) or California gulls ( L. californicus ). A minimum of 15,960 ducklings including 9,300 mallards and 5,150 gadwalls hatched on 4.5-ha Island A. Hatching rates of eggs in successful nests averaged 83% for mallards and 87% for gadwalls. Despite the close spacing of nests, most individual hens maintained normal nesting regimes. Eighty-one percent of the mallard clutches contained 7-13 eggs and 81% of the gadwall clutches contained 8-14 eggs. Island A in Miller Lake provides an outstanding example of the potential for high reproduction levels of mallards and gadwalls nesting in small areas of predator-free habitats.

North Dakota↗
USGS1982

Age-class determination of canvasbacks

A technique was developed to distinguish yearling from adult canvasbacks ( Aythya valisineria ) in the field during spring on the basis of white flecking on the distal ends of selected wing feathers. Covert feathers from adults had well-defined vermiculation patterns whereas feathers from yearlings lacked such markings. These age-related characters were confirmed by paired comparisons of feathers from the same captive birds in consecutive years and by discriminant analysis of feathers using densitometric measurements from known-age wild birds. Reflective densitometric measurements of greater secondary coverts for females and males were significantly different between 1- and 2-year-old and between 2- and 3-year-old canvasbacks. Greater secondary coverts were the best feathers for recognizing age-classes of males and females. Densitometric values indicate low variability among different observers and within samples.

Journal of Wildlife Management↗