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Lewis M. Cowardin

Publications and source records attributed to Lewis M. Cowardin.

10 recordsLinked to original sources
USGS1997

Wetland use, settling patterns, and recruitment in mallards

The correlation between number of May ponds in the Prairie Pothole Region (PPR) of North America and size of the continental mallard (Anas platyrhynchos) breeding population the following spring weakened from the 1950s to the 1980s, suggesting possible changes in suitability of prairie ponds for meeting reproductive needs. We studied wetland use and preferences of radioequipped female mallards by reproductive stage (1988-90) in eastern North Dakota and westcentral Minnesota and evaluated effect of land use on pair distribution in eastern North Dakota (1987-91). May pond density varied among years and study areas, with changes in number of temporary and seasonal ponds accounting for 93% of variation in total ponds. During all reproductive stages, semipermanent basins were used most by females, but temporary and seasonal ponds were preferred during prenesting and egg production. Accounting for number of relocations, number of ponds used varied by year, by reproductive stage and with pond density during egg production. Numbers of breeding mallard pairs in stratum 46 in eastern North Dakota increased as May ponds increased from 1963 to 1985, but 33,659 fewer breeding pairs on average were present in 1971-85 than in 1963-70. Number of breeding pairs declined relative to May ponds from the 1960s to the 1980s, probably because fewer pairs settle in temporary and seasonal ponds as the percent of landscape in cropland increases. Waterfowl managers in the PPR should target efforts to increase duck production on landscapes where non-cropped temporarily and seasonally flooded wetland habitats are plentiful, thereby increasing cost effectiveness of management actions taken to increase nest success rate.

Journal of Wildlife Management↗
USGS1995

Factors associated with duck nest success in the prairie pothole region of Canada

Populations of some dabbling ducks have declined sharply in recent decades and information is needed to understand reasons for this. During 1982-85, we studied duck nesting for 1-4 years in 17 1.6 by 16.0-km, high-density duck areas in the Prairie Pothole Region (PPR) of Canada, 9 in parkland and 8 in prairie. We estimated nest-initiation dates, habitat preferences, nest success, and nest fates for mallards ( Anas platyrhynchos ), gadwalls ( A. strepera ), blue-winged teals ( A. discors ), northern shovelers ( A. clypeata ), and northern pintails ( A. acuta ). We also examined the relation of mallard production to geographic and temporal variation in wetlands, breeding populations, nesting effort, and hatch rate. Average periods of nest initiation were similar for mallards and northern pintails, and nearly twice as long as those of gadwalls, blue-winged teals, and northern shovelers. Median date of nest initiation was related to presence of wet wetlands (contained visible standing water), spring precipitation, and May temperature. Length of initiation period was related to presence of wet wetlands and precipitation in May, June temperature, and nest success; it was negatively related overall to drought that prevailed over much of Prairie Canada during the study, especially in 1984. Mallards, gadwalls, and northern pintails nested most often in brush in native grassland, blue-winged teals in road rights-of-way, and northern shovelers in hayfields and small (< 2 ha) untilled tracts of upland habitat (hereafter called Odd area). Among 8 habitat classes that composed all suitable nesting habitat of each study area, nest success estimates averaged 25% in Woodland, 19% in Brush, 18% in Hayland, 16% in Wetland, 15% in Grass, 11% in Odd area, 8% in Right-of-way, and 2% in Cropland. We detected no significant difference in nest success among species: mallard (11%), gadwall (14%), blue-winged teal (15%), northern shoveler (12%), and northern pintail (7%). Annual nest success (pooled by study area and averaged [unweighted] over all study areas) was 17% in 1982, 15% in 1983, 7% in 1984, and 14% in 1985. We estimated that predators destroyed 72% of mallard, gadwall, blue-winged teal, and northern shoveler nests and 65% of northern pintail nests. In prairie, average nest success decreased about 4 percentage points for every 10 percentage points increase in Cropland, suggesting that under conditions of 1982-85, local populations of these species probably were not stable when Cropland exceeded about 56% of available habitat. We found recent remains of 573 dead ducks during 1983-85; most were females (Anas spp.) apparently killed by predators. In some years, mallards and northern pintails were more numerous among dead ducks than we expected. More females than males were found dead among mallards and northern shovelers, suggesting higher vulnerability of females. Of factors we examined, nest-success rate appeared to be the most influential factor in determining mallard production. Nest success varied both geographically and annually.

Prairie pothole region↗
USGS1995

Evaluations of duck habitat and estimation of duck population sizes with a remote-sensing-based system

During 1987-90, we used high-altitude photography, aerial videography, counts, and models to estimate sizes of breeding populations of dabbling ducks (Anatinae) and duck production and to identify duck habitat on U.S. Fish and Wildlife Service land and easements and on private land in the prairie pothole region of the United States. The study area contained about 3.1 million wetland basins (28,490 km2). Wetland area (ha per km2) was highest on service-owned land; wetland-basin density was greatest on service easements. Temporary and seasonal wetlands were underrepresented and lakes were overrepresented on service-owned land. Seventy-eight percent of all basins were less than 0.41 ha. Cropland dominated private land. Pond density decreased from 4.4/km2 in 1987 to 3.4/km2 in 1990 and pond area, from 7.2 ha/km2 to 2.7 ha/km2. The density of the blue-winged teal was greatest (3.4 pairs/km2) and was followed in magnitude by those of the mallard (2.1 pairs/km2), the gadwall (1.8 pairs/km2), the northern pintail (0.8 pairs/km2), and the redhead (0.8 pairs/km2). Duck density was consistently highest on service-owned land. The decline of breeding-population sizes in 1987-90 closely corresponded to losses of pond numbers and pond area. The density of breeding pairs per pond was inversely related to pond density, suggesting that breeding ducks tended to concentrate on the remaining ponds as drought intensified. The production of recruits followed the same pattern as breeding-population sizes. We estimated that 2.5% of the ducklings hatched on service-owned land, which was 1.3% of the study area; 19.6% hatched on service easements, which were 14.2% of the study area; and 77.9% hatched on private land, which was 84.6% of the study area. Various sources of bias and sampling error and improvements to the system are discussed.

Biological Science Report↗
USGS1987

A model of the productivity of the mallard duck

This paper describes a stochastic computer model that simulates recruitment of the mallard ( Anas platyrhynchos ) under different habitat conditions and management scenarios. The model incorporates several environmental phenomena and biological relations that affect mallard recruitment. Major events include arrival of mallards in the spring, daily survival of hens, initiation of nests, selection of nest sites, survival of nests until hatching, and survival of broods until fledging. The model was originally developed as a tool for synthesizing the results of research. Subsequently, we applied the model to a variety of management situations. We also describe the sources of estimates used in the model, evaluate its sensitivity to input parameters, and review some practical applications.

Ecological Modelling↗
USGS1986

Spring and summer survival of female mallards from northcentral Minnesota

Seasonal survival of 109 adult female mallards ( Anas platyrhynchos ) fitted with radio transmitters was evaluated in northcentral Minnesota during 1968-74. Survival rates for the 169-day breeding and postbreeding period were: 1.0 during nest initiation (36 days), 0.798 during incubation (28 days), 0.943 during brood rearing (51 days), 0.947 during molt (26 days), and 1.0 during premigration (28 days). Survival for the 169-day spring-summer period was 0.713 for adult females remaining on the study area. Fall-winter survival was estimated at 0.881 for those adult birds remaining on the study area throughout the summer. The data confirm speculation on relative risk to females of various phases of the mallard reproductive cycle and support previous conclusions that the northcentral Minnesota breeding mallard population is not self sustaining. The value of learning further details of processes affecting specific seasonal mortality factors for both adult and young waterfowl is emphasized.

Minnesota↗
USGS1981

Procedures for the use of aircraft in wildlife biotelemetry studies

This is a report on the state of the art methodology and on questions that arise while one is preparing to use aircraft in a biotelemetry study. In general the first step in preparing to mount an antenna on an aircraft is to consult with a certified aircraft mechanic. Aircraft certification is discussed to provide background information concerning the role of the Federal Aviation Administration (FAA) in regulating the use of biotelemetry antennas on aircraft. However, approval of any specific design of antenna mount rests with local FAA authority. Airplane and helicopter antenna attachments are described. Performance of the receiving antenna system is discussed with emphasis on how variables as aircraft type and antenna configuration may influence reception. The side-looking vs. front-looking antenna configuration and the VHF vs. HF frequency band are generally recommended for most aerial tracking studies. Characteristics of receivers, transmitters, and antennas that might influence tracking are discussed. Specific topics such as calibration of receivers and transmitter quality control are considered. Suggestions in preparing for and conducting tracking flights that will improve overall efficiency and safety are presented. Search techniques, including procedures for conducting large and specific area surveys as well as methods to improve and evaluate search efficiency, are discussed. A concluding section considers special topics such as low-level operations and the use of helicopters. Diagrams of antenna mounts, equipment check-off lists, and antenna test procedures are included as appendices.

Resource Publication↗
USGS1967

Stump and tree nesting by mallards and black ducks

Studies conducted 1961-65 at the Montezuma National Wildlife Refuge in New York demonstrated that mallards ( Anas platyrhynchos ) and black ducks ( Anas rubripes ) make extensive use of stumps and dead snags for nest sites. Nest densities in timbered habitats compared favorably with those in untimbered habitats. Nest success was generally higher in timbered than in untimbered areas, except for a newly flooded impoundment where nest success was poor. A simple artificial nest structure was used to increase the number of available nest sites in some of the timbered habitats. Development of stump-nesting populations of ducks may furnish a means of increasing waterfowl production in forested areas.

New York↗
USGS1965

An automatic camera device for measuring waterfowl use

A Yashica Sequelle camera was modified and equipped with a timing device so that it would take pictures automatically at 15-minute intervals. Several of these cameras were used to photograph randomly selected quadrats located in different marsh habitats. The number of birds photographed in the different areas was used as an index of waterfowl use.

Journal of Wildlife Management↗