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Geology topics

J.R. Sauer

Publications and source records attributed to J.R. Sauer.

At least 91 records · Page 5Linked to original sources
USGS1998

Effect of restrictive harvest regulations on survival and recovery rates of American black ducks

Population management of waterfowl requires an understanding of the effects of changes in hunting regulations on harvest and survival rates. Mean survival and recovery rates of American black ducks (Anas rubripes) were estimated during 3 periods of increasingly restrictive harvest regulations: 1950-66, 1967-82, and 1983-93. From the first to the second period, direct recovery rates declined for at least 1 age class in 4 of 6 reference areas, with a mean decline of 14% for adult and 7% for immature black ducks. From the second to the third period, direct recovery rates declined in all areas, declines averaging 37% for adults and 27% for immatures. Estimated mean survival rates increased from the first to the second period, consistent with a model of additivity of hunting mortality. Limited evidence existed for increases in survival rates from the second to the third period for immature males. For adults, however, survival increased less between these periods than would be expected if hunting mortality were additive and changes in recovery rates were proportional to changes in hunting mortality. Changes in survival and recovery rates of black ducks banded postseason were similar to those of adults banded preseason. Comparisons among estimates by degree blocks of latitude and longitude indicate that, at least between 1967 and 1983, estimated survival rates of immature and adult black ducks were lower in areas with high direct recovery rates. Smaller samples of banded birds and changes in banding locations in recent years may be limiting ability to evaluate consequences of recent changes in harvest rates. These correlation-based studies are limited in their ability to explain causes of observed changes in survival rates, suggesting the need for alternative approaches such as adaptive harvest management to increase understanding of the effects of hunting on black duck populations.

Journal of Wildlife Management↗
USGS1998

Effects of landscape composition and wetland fragmentation on frog and toad abundance and species richness in Iowa and Wisconsin, USA [abstract]

We examined the relationships between anuran diversity and landscape features in the Upper Midwestern United States. Anuran relative abundance and species richness were measured using data collected by Wisconsin and Iowa state calling surveys conducted from 1990-1995. Landscape features surrounding survey points were determined using National Wetland Inventory and Wisconsin Wetland Inventory maps. We tested several hypotheses suggested by the literature. We hypothesized that the relative abundance and species richness of anurans that breed in ephemeral wetlands is positively correlated with the surrounding area of temporary wetlands and emergent wetlands. We hypothesized that the relative abundance and species richness of anurans is positively correlated with patch diversity and wetland edges, in the absence of local fragmentation effects. We hypothesized that the relative abundance and species richness of anurans is positively associated with forests but negatively associated with agriculture and urban areas. Our results show that the interspersion of different wetland types and the concomitant increase in wetland edge habitats were generally positive for frogs and toads and anuran abundance and diversity were generally higher in association with forests, especially forested wetlands. The presence of agriculture did not always depress frog and toad populations or diversity; some species were associated with agricultural landscapes. The two states differed in how anurans were associated with landscape features like lakes and permanent wetlands. We found that frog and toad relative abundance and diversity were lower when urban areas were present. Managers can use models like ours, generated from landscape analyses, along with range maps and population trend analyses to get a comprehensive picture of the health of individual species and groups of species. Our models could be applied to the landscape as a whole, and used to predict species relative abundance and richness at new locations. Our work provides a framework for future experimental and intensive research on specific factors affecting the health of amphibians in the Upper Midwest.

Book chapter↗
USGS1997

A citywide breeding bird survey for Washington, D.C.

`DC Birdscape' was initiated in 1993 to systematically count the birds occurring throughout Washington D.C. during the breeding season. It involved a coordinated planning effort and partnership between the Audubon Naturalist Society, the National Park Service, and the National Biological Survey, and engaged the participation of more than 100 volunteers. A method for rapidly assessing the status of bird populations over a large area was developed and incorporated into a Geographic Information System to allow a multidimensional analysis of species presence and abundance across a variety of urban land use areas. A total of 91 species were observed, with an estimated total number of 115, making Washington D.C. almost as `bird rich' as nearby suburban counties. Data from the study clearly indicate that avian species are not randomly distributed throughout the Washington D.C. metropolitan area, and show affinity, at least in part, to some of the most broadly recognized land use patterns that are commonly used to zone and classify urban areas under development schemes. This study represents a prototype that will allow efficient and economical monitoring of urban bird populations.

Washington, D.C.↗
USGS1997

Population trends of black terns from the North American Breeding Bird Survey, 1966-1996

Data from the North American Breeding Bird Survey indicate a survey-wide decline in Black Terns (Chlidonias niger) at an average rate of 3.1% annually during 1966-1996. Black Terns in Canada decreased at an average annual rate of 3.5% during this interval, while the United States population showed no significant trends. The long-term declines largely reflect trends prior to 1980, when the continental, Canadian, and United States populations decreased at average annual rates of 7.5%, 5.6%, and 11.9%, respectively. Most population trends were reversed during the 1990s, causing trend estimates over the 1980-1996 interval to become more positive. Associations between patterns of change in Black Terns, Mallards (Anas platyrhynchos), and numbers of ponds in the northern Great Plains suggest some relationships exist between habitat availability and the population trajectories.

Colonial Waterbirds↗
USGS1997

Estimation of population trajectories from count data

Monitoring of changes in animal population size is rarely possible through complete censuses; frequently, the only feasible means of monitoring changes in population size is to use counts of animals obtained by skilled observers as indices to abundance. Analysis of changes in population size can be severely biased if factors related to the acquisition of data are not adequately controlled for. In particular we identify two types of observer effects: these correspond to baseline differences in observer competence, and to changes through time in the ability of individual observers. We present a family of models for count data in which the first of these observer effects is treated as a nuisance parameter. Conditioning on totals of negative binomial counts yields a Dirichlet compound multinomial vector for each observer. Quasi-likelihood is used to estimate parameters related to population trajectory and other parameters of interest; model selection is carried out on the basis of Akaike's information criterion. An example is presented using data on Wood thrush from the North American Breeding Bird Survey.

Biometrics↗
USGS1997

Monitoring Canadian bird populations with winter counts

Two winter bird surveys in Canada have range-wide population monitoring potential: Christmas Bird Counts (CBCs) and Project FeederWatch (PFW). CBC trends are shown to be correlated to Breeding Bird Survey (BBS) trends, whether or not part of the winter range lies outside the CBC coverage area. Some species are poorly covered by this survey (e.g. seabirds, nocturnal species, and Neotropical migrants). Only eight Canadian breeding species that are not sampled by the BBS have their winter range well-covered by the CBC, but the CBC should be valuable as an independent source of trend data for many more species, including northern nesters with only marginal BBS coverage. More work is needed to show whether PFW trends match BBS trends; even if they do, PFW covers relatively few species, and most are monitored already by the BBS and/or CBC

Book chapter↗
USGS1997

Population trends of Black Terns from the North American Breeding Bird Survey, 1966-1996

Data from the North American Breeding Bird Survey indicate a survey-wide decline in Black Terns (Chlidonias niger) at an average rate of 3.1% annually during 1966-1996. Black Terns in Canada decreased at an average annual rate of 3.5% during this interval, while the United States population showed no significant trends. These long-term declines largely reflect trends prior to 1980, when the continental, Canadian, and United States populations decreased at average annual rates of 7.5%, 5.6%, and 11.9%, respectively. Most population trends were reversed during the 1990s, causing trend estimates over the 1980-1996 interval to become more positive. Associations between patterns of change in Black Terns, Mallards (Anas platyrhynchos), and numbers of ponds in the northern Great Plains suggest some relationships exist between habitat availability and the population trajectories.

Waterbirds↗
USGS1996

First-time observer effects in the North American Breeding Bird Survey

Currently the operational analysis of Breeding Bird Survey (BBS) data by the National Biological Service accounts for observer differences in estimating the trend for each route, but within-observer differences are not modeled. We tested for the existence of a form of within-observer differences in skill level, namely a change in ability to count birds of a given species after an observer's first year on a given route. An increase in ability could positively bias the trend estimate. Removal of an observer's first year of observation on each route for the period 1966 to 1991 resulted in lower average unweighted trend estimates for 415 of 459 species (90%). These reductions were statistically significant for 213 species (46%). The average reduction in trend was 1.8% change per year (SD = 5.4%). In route-regression analysis, route data are weighted by a measure of precision. Removing first-year observer counts reduced the weighted trend estimate for 275 of 416 species (66%), but differences generally were small.

The Auk↗
USGS1996

The 1994 and 1995 summary of the North American Breeding Bird Survey

Data from the North American Breeding Bird Survey were used to estimate continental and regional changes in bird populations for the 2-year periods of 1993-1994 and 1994-1995. These 2-year changes were placed in the context of population trends estimated over the 1966-1995 interval. The 2-year changes were more positive during the 1993-1994 period, when 54.2% of all species exhibited positive continental trend estimates. This percentage was reduced to 47.7% during 1994-1995, as compared with 50.5% of all species having positive continental trend estimates over then entire survey period. In general, the percentage of increasing species in the Central and Western BBS regions was highest during 1993-1994, with a very marked decline in the Western BBS Region during 1994-1995. The percentage was highest in the Eastern BBS Region during 1994-1995. The continental and regional percentages of species with positive trend estimates were also analyzed for 12 groups of North American birds having shared life-history traits. Over the entire survey period, grassland birds remain the species group with the smallest percentage of increasing species. Trends during these 2-year intervals do not indicate any consistent improvement in the overall declines experienced by grassland birds since the mid-1960s.

Bird Populations↗
USGS1995

Acephate affects migratory orientation of the white-throated sparrow (Zonotrichia albicollis)

Migratory white-throated sparrows ( Zonotrichia albicollis ) were exposed to acephate (acetylphosphoramidothioic acid O, S -dimethyl ester), an organophosphorus pesticide, to determine its effects on migratory orientation and behavior. Birds were also exposed to polarizer sheets to determine the mechanism by which acephate may affect migratory orientation. Adult birds exposed to 256 ppm acephate a.i. were not able to establish a preferred migratory orientation and exhibited random activity. All juvenile treatment groups displayed a seasonally correct southward migratory orientation. We hypothesize that acephate may have produced aberrant migratory behavior by affecting the memory of the migratory route and wintering ground. This experiment reveals that an environmentally relevant concentration of a common organophosphorus pesticide can alter migratory orientation, but its effect is markedly different between adult and juvenile sparrows. Results suggest that the survival of free-flying adult passerine migrants may be compromised following organophosphorus pesticide exposure.

Environmental Toxicology and Chemistry↗
USGS1995

Estimation and confidence intervals for empirical mixing distributions

Questions regarding collections of parameter estimates can frequently be expressed in terms of an empirical mixing distribution (EMD). This report discusses empirical Bayes estimation of an EMD, with emphasis on the construction of interval estimates. Estimation of the EMD is accomplished by substitution of estimates of prior parameters in the posterior mean of the EMD. This procedure is examined in a parametric model (the normal-normal mixture) and in a semi-parametric model. In both cases, the empirical Bayes bootstrap of Laird and Louis (1987, Journal of the American Statistical Association 82, 739-757) is used to assess the variability of the estimated EMD arising from the estimation of prior parameters. The proposed methods are applied to a meta-analysis of population trend estimates for groups of birds.

Biometrics↗
USGS1995

Statistical aspects of point count sampling

The dominant feature of point counts is that they do not census birds, but instead provide incomplete counts of individuals present within a survey plot. Considering a simple model for point count sampling, we demon-strate that use of these incomplete counts can bias estimators and testing procedures, leading to inappropriate conclusions. A large portion of the variability in point counts is caused by the incomplete counting, and this within-count variation can be confounded with ecologically meaningful varia-tion. We recommend caution in the analysis of estimates obtained from point counts. Using; our model, we also consider optimal allocation of sampling effort. The critical step in the optimization process is in determining the goals of the study and methods that will be used to meet these goals. By explicitly defining the constraints on sampling and by estimating the relationship between precision and bias of estimators and time spent counting, we can predict the optimal time at a point for each of several monitoring goals. In general, time spent at a point will differ depending on the goals of the study.

Book chapter↗