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At least 145 records · Page 8Linked to original sources
USGS1981

The Mayfield method of estimating nesting success: A model, estimators and simulation results

Using a nesting model proposed by Mayfield we show that the estimator he proposes is a maximum likelihood estimator (m.l.e.). M.l.e. theory allows us to calculate the asymptotic distribution of this estimator, and we propose an estimator of the asymptotic variance. Using these estimators we give approximate confidence intervals and tests of significance for daily survival. Monte Carlo simulation results show the performance of our estimators and tests under many sets of conditions. A traditional estimator of nesting success is shown to be quite inferior to the Mayfield estimator. We give sample sizes required for a given accuracy under several sets of conditions.

The Wilson Bulletin↗
USGS1984

DDE in birds' eggs: Comparisons of two methods for estimating critical levels

The sample egg technique and eggshell thickness-residue regression analysis were comparatively evaluated as tools in estimating critical levels of DDE in birds? eggs that seriously affect reproductive successa nd population starts....In comparing critical values of DDE that were derived from the two methods, the estimates were lower using the sample egg technique for both the Brown Pelican (3 ?g/g vs 8 ?g/g) and the Black-crowned Night-Heron (12?g/g/ vs 54 ?g/g) assuming a critical value of eggshell thinning at 20%....Extension of the regression line beyond the eggshell thickness-DDE residue data base is likely to result in spurious critical values of DDE. When sufficient thickness and residue data are available for estimating critical values of DDE from the regression equation, the estimates are meaningful but are likely to be inflated because adverse effects unrelated to eggshell thinning such as parental behavior and embryotoxicity unrelated to eggshell deficiencies are not taken into account.....Establishing critical levels of pollutants in eggs and tissues is a necessary procedure in assessing effects of these chemicals on individuals and populations of sensitive species. There are inherent difficulties in quantifying the effects of any pollutant on population trends and declines in productivity. The sample egg technique is apparently a more sensitive method for estimating critical levels of DDE, but some subjective interpretation is required for results obtained by both methods.

The Wilson Bulletin↗
USGS1985

Brown pelican populations and pollutants in Texas 1975-1981

The population status, reproductive success, and levels of environmental contaminants in brown pelicans (P. occidentalis) in Texas were studied from 1975 through 1981. Breeding populations increased from 18 pairs in 1975 to 57 pairs in 1981. All unhatched eggs salvaged for analyses of contaminant residues contained DDT metabolites. Mean DDE levels varied from 0.9 to 2.4 ppm and about 7% of the samples had residues that approached critical levels that could affect reproductive success. DDE levels did not decline from 1975 to 1981 and residues leveled off at higher values than those in South Carolina and Louisiana pelican populations. PCB [polychlorinated biphenyl] residues also remained stable. Endrin was detected only in 1975.

The Wilson Bulletin↗
USGS1989

Kirtland's warblers on the nesting grounds during the post- breeding period

Information indicates that a substantial number of breeding birds remain in Michigan through September, and a few individuals probably remain into early October. Migration apparently consists of two waves of migrants: an early departure (mid-August to early September); and late departure (late September). Based on our findings, we recommend that major Kirtland's warbler areas be kept closed into mid-September.

The Wilson Bulletin↗
USGS1989

Additional records of birds from Cat Island, Bahamas

During 11-15 March 1986, we visited Cat Island in the Bahamas. Here we report on 27 species of birds whose status on Cat Island is poorly known, including eight for which no pervious records exist.

The Wilson Bulletin↗
USGS1978

Habitat selection by breeding red-winged blackbirds

Habitat preferences of breeding Red-winged Blackbirds in an agricultural area were determined by comparing population density, landscape characteristics, and vegetational descriptions. Observations were made throughout the breeding season. Preferred breeding habitats of Red-wings, in order of preference, were wetlands, hayfields, old fields, and pastures. Males and females occupied old fields and wetlands first, then hayfields, and finally, pastures. Cutting of hayfields caused territorial abandonment by both sexes within 48 h. The apparent movement of displaced females from cut hayfields to uncut hayfields suggests that habitat fidelity of females is strong after the breeding effort has begun. Breeding Red-wings exhibited general preferences for trees, large amounts of habitat edge, erect old vegetation, and sturdy, tall, and dense vegetation. Vegetative forms and species, such as upland grasses, broad- and narrow-leafed monocots in wetlands, and forbs were important to the Red-wing at various times during the breeding season. Landscape and vegetational preferences of breeding adults were easier to observe early in the breeding season (March through May) than later. Vegetational growth and increases in the size of the breeding population probably make these preferences more difficult to detect. Territory size was poorly correlated with landscape and vegetational characteristics in uplands but strongly correlated with broad- and narrow-leafed mono cots and vegetative height in wetlands. Wetland territories were smaller than upland territories. Territories increased in size during the middle and late portions of the breedi g season. Habitat selection by the Red-winged Blackbird can best be studied by evaluating vegetative preferences throughout the breeding season.

The Wilson Bulletin↗
USGS1990

Ecology, behavior, and conservation of the Poo-uli (Melamprosops phaeosoma)

Studies of the population density, habitat structure, foraging behavior, and activity budgets of the Poo-uli (Melamprosops phaeosoma) were conducted intermittently between 1973 and 1985 in a 50-ha study area in the upper Hanawi watershed, island of Maui, Hawaii. Poo-uli have apparently declined in density on this site by 80% from 1975 to 1981 and by 90% from 1975 to 1985. During this period, pig activity, as indexed by ground cover disturbance, increased 473%. Compared to values in the range of the Poo-uli, pig activity was 9-24 times greater in two adjacent out-of-range areas. Poo-uli most frequently foraged from 4-7 m height on ohia (Metrosideros polymorpha), olapa (Cheirodendron trigynum), ohelo (Vaccinium calycinum), and kanawao (Broussaisia arguta) in decreasing frequency; feeding on kanawao was significantly more frequent than random expectation. Chief food items were land snails and insects. Most prey were captured on branches from under moss, lichen, and bark by gleaning, probing, and pecking. Birds spent 48% of their daylight hours foraging and 30% quietly perching. Poo-uli frequently formed small mixed-species flocks, usually with Maui Creepers (Puroreomyza montana), that probably facilitated predator avoidance and foraging efficiency. The major limiting factors at present appear to be habitat modification from feral pigs (Sus scrofa), predation, avian disease, interspecific competition from the introduced garlic snail (Oxychilus alliarius), and possibly gene pool impoverishment. Control of pigs is recommended.

The Wilson Bulletin↗
USGS1990

Recent population trends of the eastern bluebird

North American Breeding Bird Survey data for the period 1966-1987 indicate that Eastern Bluebird (Sialia sialis) populations declined during the 1970s, primarily in association with either severe winters or severe spring storms. In recent years, bluebird populations have increased to levels similar to those observed during the first year (1966) of the survey. Survey results suggest that climate has an important role in affecting short-term population declines in bluebirds.

The Wilson Bulletin↗
USGS1991

Approaches to the conservation of coastal wetlands in the Western Hemisphere

Coastal wetlands rank among the most productive and ecologically valuable natural ecosystems on Earth. Unfortunately, they are also some of the most disturbed. Because they are productive and can serve as transportation arteries, coastal wetlands have long attracted human settlement. More than half of the U.S. population currently lives within 80 km of its coasts, and one estimate places 70% of all humanity in the coastal zone. Human impacts to coastal wetlands include physical alteration of hydrological processes; the introduction of toxic materials, nutrients, heat, and exotic species; and the unsustainable harvest of native species. Between 1950 and 1970, coastal wetland losses in the U.S. averaged 8 100 ha/year. In Central and South America, development pressures along the coastal zone rank among the most serious natural resource problems in the region..... Here, we (1) briefly describe coastal wetland avifauna, (2) discuss the threat of global warming on coastal wetlands, (3) use several Western Hemisphere wetlands as site-specific examples of development pressures facing these habitats, and (4) provide synopses of nongovernmental and governmental approaches to wetland conservation. Overall, we provide a socio-economic context for conservation of coastal wetlands in the Western Hemisphere. We suggest that efforts aimed at conserving sites of particular importance for their biological diversity should be pursued within a framework of wise use that addresses the broader issues of human population growth and economic development.

The Wilson Bulletin↗