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At least 289 records · Page 16Linked to original sources
USGS2002

Loss of sagebrush ecosystems and declining bird populations in the Intermountain West: Priority research issues and information needs

Sagebrush lands in the Intermountain West are declining rapidly in quality and extent. Consequently, populations of many bird species dependent on these ecosystems also are declining. The greater sage-grouse has been petitioned for listing as a threatened and endangered species, and other species of sagebrush-obligate birds have special conservation status in most states. We identified the primary issues and information needs during a multi-agency workshop, conducted in response to concerns by management agencies related to declining bird population trends in sagebrush habitats. Priority needs were to (1) obtain a better understanding of bird response to habitat and landscape features, (2) develop monitoring designs to sample habitats and bird populations, (3) determine the effects of land use on sagebrush habitats and dependent bird species, and (4) identify linkages between breeding and wintering ranges. This agenda will identify causes and mechanisms of population declines in birds dependent on sagebrush ecosystems and will lead to better management of the ecosystems upon which they depend.

Fact Sheet↗
USGS2005

Influence of Riparian Tree Phenology on Lower Colorado River Spring-Migrating Birds: Implications of Flower Cueing

Executive Summary Neotropical migrant birds make choices about which habitats are most likely to provide successful foraging locations during migration, but little is known about how these birds recognize and process environmental clues that indicate the presence of prey species. Aspects of tree phenology, notably flowering of trees along the lower Colorado River corridor, coincide with the migratory stopovers of leaf-gleaning insectivorous songbirds and may be an important indicator of arthropod prey species availability. Shifting tree flowering and leaf flush during the spring migration period presents avian insectivores with an assortment of foraging opportunities. During two field seasons at Cibola National Wildlife Refuge in southwestern Arizona, we examined riparian tree species to test whether leaf-gleaning insectivorous birds are attracted to the flowering condition of trees in choosing foraging sites. We predicted that flowering trees would host more insect prey resources, would thus show increased visit rates, length of stays and attack ratios of migrant avian insectivores, and that those arthropods would be found in the stomach contents of the birds. Paired trees of honey mesquite (Prosopis glandulosa), displaying heavy and light degrees of flowering were observed to test these predictions. To test whether birds are tracking arthropods directly or are using flowers as a proximate cue, we removed flowers from selected trees and paired these treated trees with neighboring high flowering trees, which served as controls. Avian foraging behavior, avian diets, arthropods, and phenology data were collected at the same time to control for temporal differences in insect availability, plant phenology, and differences in stopover arrivals of birds. We documented five patterns from this study: 1) Higher abundance and richness of arthropods were found on honey mesquite trees with greater numbers of flowers. 2) Arthropod abundance and richness increased as flowering level increased. 3) The subset of migrant avian insectivores selected for study disproportionately foraged among honey mesquite trees with significantly greater amounts of flower coverage than they did on trees with less than average flower coverage. 4) Paired field experiments demonstrated that migrant avian insectivores more often visited, stayed longer, and had higher attack rates on insect prey in honey mesquite trees with greater numbers of flowers. 5) Diet analyses of selected avian insectivores showed over half of their diet consisted of prey significantly associated with honey mesquite flowering. Combined, these results suggest that honey mesquite flowering condition is an important cue used by avian insectivores that enables birds to quickly find arthropod prey at stop-over locations, while in transit during spring migration.

Open-File Report↗
USGS2014

Projecting climate effects on birds and reptiles of the Southwestern United States

We modeled the current and future breeding ranges of seven bird and five reptile species in the Southwestern United States with sets of landscape, biotic (plant), and climatic global circulation model (GCM) variables. For modeling purposes, we used PRISM data to characterize the climate of the Western United States between 1980 and 2009 (baseline for birds) and between 1940 and 2009 (baseline for reptiles). In contrast, we used a pre-selected set of GCMs that are known to be good predictors of southwestern climate (five individual and one ensemble GCM), for the A1B emission scenario, to characterize future climatic conditions in three time periods (2010–39; 2040–69; and, 2070–99). Our modeling approach relied on conceptual models for each target species to inform selection of candidate explanatory variables and to interpret the ecological meaning of developed probabilistic distribution models. We employed logistic regression and maximum entropy modeling techniques to create a set of probabilistic models for each target species. We considered climatic, landscape, and plant variables when developing and testing our probabilistic models. Climatic variables included the maximum and minimum mean monthly and seasonal temperature and precipitation for three time periods. Landscape features included terrain ruggedness and insolation. We also considered plant species distributions as candidate explanatory variables where prior ecological knowledge implicated a strong association between a plant and animal species. Projected changes in range varied widely among species, from major losses to major gains. Breeding bird ranges exhibited greater expansions and contractions than did reptile species. We project range losses for Williamson’s sapsucker and pygmy nuthatch of a magnitude that could move these two species close to extinction within the next century. Although both species currently have a relatively limited distribution, they can be locally common, and neither are presently considered candidates for prospective endangerment. We project range losses of over 40 percent, from its current extent of occurrence, for the plateau striped whiptail, Arizona black rattlesnake, and common lesser earless lizard. Currently, these reptile species are thought to be common or at least locally abundant throughout their ranges. The total contribution of plants in each distribution model was very small, but models that contained at least one plant always outperformed models with only physical variables (climatic or landscape). The magnitude of change in projected range increased further into the future, especially when a plant was in the model. Among bird species, those that had the strongest association with a landscape feature during the breeding season, such as terrain ruggedness and insolation, exhibited the smallest contractions in projected breeding range in the future. In contrast, bird species that had weak associations with landscape features, but strong climatic associations, suffered the greatest breeding range contractions. Thus, landscape effects appeared to buffer some of the negative effects of climate change for some species. Among bird species, magnitude of change in projected breeding range was positively related to the annual average temperature of their baseline distribution, thus species with the warmest breeding ranges exhibited the greatest changes in future breeding ranges. This pattern was not evident for reptiles, but might exist if additional species were included in the model. Our results provide managers with a series of projected range maps that will enable scientists, concerned citizens, and wildlife managers to identify what the potential effects of climate change will be on bird and reptile distributions in the Western United States. We hope that our results can be used in proactive ways to mitigate some of the potential effects of climate change on selected species.

Colorado Plateau;Sonoran Desert↗
USGS2014

Effects of reintroduced beaver ( Castor canadensis ) on riparian bird community structure along the upper San Pedro River, southeastern Arizona and northern Sonora, Mexico

Chapter 1.—We measured bird abundance and richness along the upper San Pedro River in 2005 and 2006, in order to document how beavers ( Castor canadensis ) may act as ecosystem engineers after their reintroduction to a desert riparian area in the Southwestern United States. In areas where beavers colonized, we found higher bird abundance and richness of bird groups, such as all breeding birds, insectivorous birds, and riparian specialists, and higher relative abundance of many individual species—including several avian species of conservation concern. Chapter 2.—We conducted bird surveys in riparian areas along the upper San Pedro River in southeastern Arizona (United States) and northern Sonora (Mexico) in order to describe factors influencing bird community dynamics and the distribution and abundance of species, particularly those of conservation concern. These surveys were also used to document the effects of the ecosystem-altering activities of a recently reintroduced beavers ( Castor canadensis ). Chapter 3.—We reviewed Southwestern Willow Flycatcher ( Empidonax traillii extimus ) nest records and investigated the potential for future breeding along the upper San Pedro River in southeastern Arizona, where in July 2005 we encountered the southernmost verifiable nest attempt for the species. Continued conservation and management of the area’s riparian vegetation and surface water has potential to contribute additional breeding sites for this endangered Willow Flycatcher subspecies. Given the nest record along the upper San Pedro River and the presence of high-density breeding sites to the north, the native cottonwood-willow forests of the upper San Pedro River could become increasingly important to E. t. extimus recovery, especially considering the anticipated effect of the tamarisk leaf beetle ( Diorhabda carinulata ) on riparian habitat north of the region.

Arizona;Sonora↗
USGS2024

Seasonal and breeding phenologies of 38 grassland bird species in the midcontinent of North America

Grasslands in the midcontinent of North America are highly imperiled, and grassland birds have suffered the largest bird declines of any terrestrial biome in North America in the last 50 years. Consequently, the conservation and management of grasslands, as well as their associated avian communities, are major priorities for the State, Provincial, and Federal agencies; non-governmental organizations; and private entities that influence the millions of hectares of grasslands in the midcontinent. Resource managers often deploy disturbances to grasslands (for example, grazing, haying, and burning) to maintain or enhance their quality or structure, but the timing of these disturbances has the potential to disrupt the nesting activities of grassland birds. In this report, we compiled two types of phenology information for 38 species of nonwaterfowl, grassland-nesting birds across four author-defined regions in the midcontinent of North America: (1) species- and region-specific arrival and departure dates from the eBird database, which indicate when a species may be assumed to be present in a region; and (2) reported dates of nesting activity for each species (start and end dates of nesting as well as total duration) from published bird distribution and occurrence books and breeding bird atlases, which indicate when nesting by a species may be assumed. This previously available but widely dispersed information, compiled for the first time, will aid resource managers and inform their decisions about the timing of disturbances while minimizing grassland management effects on nesting birds.

Open-File Report↗
USGS2007

Distribution of ground-nesting marine birds along shorelines in Glacier Bay, southeastern Alaska: An assessment related to potential disturbance by back-country users

With the exception of a few large colonies, the distribution of ground-nesting marine birds in Glacier Bay National Park in southeastern Alaska is largely unknown. As visitor use increases in back-country areas of the park, there is growing concern over the potential impact of human activities on breeding birds. During the 2003–05 breeding seasons, the shoreline of Glacier Bay was surveyed to locate ground-nesting marine birds and their nesting areas, including wildlife closures and historical sites for egg collection by Alaska Native peoples. The nesting distribution of four common ground-nesting marine bird species was determined: Arctic Tern ( Sterna paradisaea ), Black Oystercatcher ( Haematopus bachmani ), Mew Gull ( Larus canus ), and Glaucous-winged Gull ( Larus glaucescens ). Observations of less abundant species also were recorded, including Herring Gull ( Larus argentatus ), Red-throated Loon ( Gavia stellata ), Canada Goose ( Branta canadensis ), Willow Ptarmigan ( Lagopus lagopus ), Semipalmated Plover ( Charadrius semipalmatus ), Spotted Sandpiper ( Actitis macularia ), Least Sandpiper ( Calidris minutilla ), Parasitic Jaeger ( Stercorarius parasiticus ), and Aleutian Tern ( Sterna aleutica ). Nesting distribution for Arctic Terns was largely restricted to the upper arms of the bay and a few treeless islets in the lower bay, whereas Black Oystercatchers were more widely distributed along shorelines in the park. Mew Gulls nested throughout the upper bay in Geikie Inlet and in Fingers and Berg Bays, and most Glaucous-winged Gull nests were found at wildlife closures in the central and lower bays. Several areas were identified where human disturbance could affect breeding birds. This study comprises the first bay-wide survey for the breeding distribution of ground-nesting marine birds in Glacier Bay National Park, providing a minimum estimate of their numbers and distribution within the park. This information can be used to assess future human disturbance and track natural changes in nesting bird distribution over time.

Alaska↗
USGS2009

Prevalence of West Nile virus in migratory birds during spring and fall migration

To investigate the role of migratory birds in the dissemination of West Nile virus (WNV), we measured the prevalence of infectious WNV and specific WNV neutralizing antibodies in birds, principally Passeriformes, during spring and fall migrations in the Atlantic and Mississippi flyways from 2001-2003. Blood samples were obtained from 13,403 birds, representing 133 species. Specific WNV neutralizing antibody was detected in 254 resident and migratory birds, representing 39 species, and was most commonly detected in northern cardinals (Cardinalis cardinalis) (9.8%, N = 762) and gray catbirds (Dumetella carolinensis) (3.2%,N = 3188). West Nile virus viremias were detected in 19 birds, including 8 gray catbirds, and only during the fall migratory period. These results provide additional evidence that migratory birds may have been a principal agent for the spread of WNV in North America and provide data on the occurrence of WNV in a variety of bird species. Copyright ?? 2009 by The American Society of Tropical Medicine and Hygiene.

American Journal of Tropical Medicine and Hygiene↗
USGS2025

Relative abundance, seasonal occurrence, and distribution of marine birds in the northern Gulf of Mexico

Marine birds in the U.S. Gulf of Mexico have long been poorly studied. Given statutory obligations to protect migratory birds and endangered species, three broad-scale vessel and aerial programs initiated since 2010 have now surveyed the entire northern Gulf. Vessel coverage alone exceeds 700 d and 74,000 km of observer effort using 300-m strip transects. We supplemented these survey data with earlier, smaller-scale studies, eBird checklists, literature reviews, and other less accessible sources to create snapshot summaries of relative abundance, seasonal occurrence, and regional distribution for 117 taxa of marine and water birds reported from the northern Gulf (113 of which were substantiated with physical evidence). Using taxonomic and functional criteria, we identified 56 taxa characteristic of open shelf, slope, and pelagic waters (federal jurisdiction), 41 taxa with primarily coastal affinities (state and federal jurisdiction), and 20 taxa of sea and diving ducks. High species richness of marine birds in the northern Gulf is attributed to (1) a temperate-to-tropical gradient facilitating diverse marine environments year-round; (2) varied geographic origins of marine bird species using the Gulf; and (3) a mostly enclosed sea basin acting as a vagrant trap for wide-ranging species. Our taxonomic list and status updates seek to bridge information gaps for marine birds now subject to accelerated commercial uses of this region's continental shelf, including newly proposed offshore wind energy development. Other applications include guiding risk and vulnerability assessments of Gulf marine birds, providing core content for seabird observer training, and prioritizing environmental impact reviews and monitoring programs in offshore energy construction and operations plans.

Marine Ornithology: Journal of Seabird Research an↗
USGS1987

Breeding birds and vegetation structure in western North Dakota wooded draws

Populations and distribution of breeding birds occupying wooded draws were studied in a five-county region of western North Dakota during June 1982. Wooded draw vegetation was dominated by green ash, which occurred in 96% of the draws sampled. Chokecherry and juneberry were the most frequent shrub species. I recorded 49 bird species in the 30 draws censused. Rufous-sided towhee, brown-headed cowbird, house wren, and American goldfinch were the most numerous bird species present. Significant correlations were found between (1) the number of live trees and bird species evenness, (2) density of dead trees and bird species diversity and richness, (3) density of shrubs with bird species evenness, and (4) foliage volume in the high ground layer and bird species evenness.

Prairie Naturalist↗
USGS1975

Distribution and density of bird species hazardous to aircraft

Only in the past 5 years has it become feasible to map the relative abundance of North American birds. Two programs presently under way and a third that is in the experimental phase are making possible the up-to-date mapping of abundance as well as distribution. A fourth program that has been used successfully in Europe and on a small scale in parts of North America yields detailed information on breeding distribution. The Breeding Bird Survey, sponsored by the U.S. Bureau of Sport Fisheries and Wildlife and the Canadian Wildlife Service, involves 2,000 randomly distributed roadside counts that are conducted during the height of the breeding season in all U.S. States and Canadian Provinces. Observations of approximately 1.4 million birds per year are entered on magnetic tape and subsequently used both for statistical analysis of population trends and for computer mapping of distribution and abundance. The National Audubon Society's Christmas Bird Count is conducted in about 1,000 circles, each 15 miles (24 km) in diameter, in the latter half of December. Raw data for past years have been published in voluminous reports, but not in a form for ready analysis. Under a contract between the U.S. Air Force and the U. S. Bureau of Sport Fisheries and Wildlife (in cooperation with the National Audubon Society), preliminary maps showing distribution and abundance of selected species that are potential hazards to aircraft are presently being mapped and prepared for publication. The Winter Bird Survey, which is in its fifth season of experimental study in a limited area in Central Maryland, may ultimately replace the Christmas Bird Count source. This Survey consists of a standardized 8-kilometer (5-mile) route covered uniformly once a year during midwinter. Bird Atlas programs, which map distribution but not abundance, are well established in Europe and are gaining interest in America

Book chapter↗
USGS1977

Impact of estuarine pollution on birds

Pollution of estuaries affects bird populations indirectly through changes in habitat and food supply. The multi-factor pollution of Chesapeake Bay has resulted in diminution of submerged aquatic plants and consequent change in food habits of the canvasback duck. Although dredge-spoil operations can improve wildlife habitat, they often result in its demise. Pollution of estuaries also affects birds directly, through chemical toxication, which may result in outright mortality or in reproductive impairment. Lead from industrial sources and roadways enters the estuaries and is accumulated in tissues of birds. Lead pellets deposited in estuaries as a result of hunting are consumed by ducks with sufficient frequency .to result m large annual die-offs from lead poisoning. Fish in certain areas, usually near industrial sources, may contain levels of mercury high enough to be hazardous to birds that consume them. Other heavy metals are present in estuarine birds, but their significance is poorly known. Oil exerts lethal or sublethal effects on birds by oiling their feathers, oiling eggs and young by contaminated parents, and by ingestion of oil-contaminated food. Organochlorine chemicals, of both agricultural and industrial origin, travel through the food chains and reach harmful levels in susceptible species of birds in certain estuarine ecosystems. Both outright mortality and reproductive impairment have occurred.

Book chapter↗
USGS1999

Demography of forest birds in Panama: How do transients affect estimates of survival rates?

Estimates of annual survival rates of neotropical birds have proven controversial. Traditionally, tropical birds were thought to have high survival rates for their size, but analyses of a multispecies assemblage from Panama by Karr et al. (1990) provided a counterexample to that view. One criticism of that study has been that the estimates were biased by transient birds captured only once as they passed through the area being sampled. New models that formally adjust for transient individuals have been developed since 1990. Preliminary analyses indicate that these models are indeed useful in modelling the data from Panama. Nonetheless, there is considerable interspecific variation and overall estimates of annual survival rates for understorey birds in Panama remain lower than those from other studies in the Neotropics and well below the rates long assumed for tropical birds (i.e. > 0.80). Therefore, tropical birds may not have systematically higher survival rates than temperate-zone species. Variation in survival rates among tropical species suggests that theory based on a simple tradeoff between clutch size and longevity is inadequate. The demographic traits of birds in the tropics (and elsewhere) vary within and among species according to some combination of historical and ongoing ecological factors. Understanding these processes is the challenge for future work.

Book chapter↗
USGS1998

Demography of forest birds in Panama: How do transients affect estimates of survival rates?

Estimates of annual survival rates for a multispecies sample of neotropical birds from Panama have proven controversial. Traditionally, tropical birds were thought to have high survival rates for their size, but analyses by Kart et al. (1990. Am. Nat. 136:277-91) contradicted that view, suggesting tropical birds may not have systematically high survival rates. A persistent criticism of that study has been that the estimates were biased by transient birds captured only once as they passed through the area being sampled. New models that formally adjust for transient individuals have been developed since 1990. Preliminary analyses using these models indicate that, despite some variation among species, overall estimates of survival rates for understory birds in Panama are not strongly affected by adjustments for transients. We also compare estimates of survival rates based on mark-recapture models with observations of colour-marked birds. The demographic traits of birds in the tropics (and elsewhere) vary within and among species according to combinations of historical and ongoing ecological factors. Understanding sources of this variation is the challenge for future work.

Book chapter↗
USGS2003

A critical look at national monitoring programs for birds and other wildlife species

Concerns?about declines in numerous taxa have created agreat deal of interest in survey development. Because birds have traditionally been monitored by a variety of methods, bird surveys form natural models for development of surveys for other taxa. Here I suggest that most bird surveys are not appropriate models for survey design. Most lack important design components associated with estimation of population parameters at sample sites or with sampling over space, leading to estimates that may be biased, I discuss the limitations of national bird monitoring programs designed to monitor population size. Although these surveys are often analyzed, careful consideration must be given to factors that may bias estimates but that cannot be evaluated within the survey. Bird surveys with appropriate designs have generally been developed as part of management programs that have specific information needs. Experiences gained from bird surveys provide important information for development of surveys for other taxa, and statistical developments in estimation of population sizes from counts provide new approaches to overcoming the limitations evident in many bird surveys. Design of surveys is a collaborative effort, requiring input from biologists, statisticians, and the managers who will use the information from the surveys.

Book chapter↗
USGS1974

The winter bird survey of central Maryland, U.S.A

A method for monitoring changes in winter bird populations was tested in central Maryland in the winters of 1970, 1971 and 1972. A systematic sample of 41 transects was established to sample an area of 6150 sq. km. Each transect, located at the center of a standard 7 1/2-minute topographic map, was 8 km in length and approximately square in shape. Coverage began at local sunrise on any one day from 15 January to 15 February, and was completed in exactly 4 hours. Birds seen or heard within one-fourth mile (0.40) km were recorded separately for each hour, and those identified at a greater distance were entered in a separate column. The mean number of species per route was 29. Ten species showed a statistically significant change from 1970 to 1971 and 8 from 1971 to 1972. The Winter Bird Survey results were compared with the results from the Audubon Society's Christmas Bird Count in the same area. Close correlation was found between the two surveys, but in general the Winter Bird Survey totals are higher except for species that frequent feeding trays and those that are conspicuous along roadsides. The Winter Bird Survey method shows much promise as a means of world-wide monitoring of bird populations; it is urged that field tests be conducted on other continents.

Acta Ornithologica↗
USGS1978

Rehabilitation of birds oiled on two mid-Atlantic estuaries

An estimated 52,500 birds died as a result of 7 major oil spills on 2 mid-Atlantic estuaries between 1973-78. Ruddy ducks ( Oxyura jamaicensis ) constituted 98% of 12,500 birds known to have died from 5 spills on the Delaware River. Seventy-six percent of 40,000 dead birds from 2 Chesapeake Bay spills were horned grebes ( Podiceps auritus ) and oldsquaw ( Clangula hyemalis ). Oiled waterfowl that were captured alive (6% of the estimated mortality) were cleaned with a variety of cleaning agents and techniques. High mortality occurred during and shortly after cleaning, and was apparently due to hypothermia and to toxicity of solvent cleaning agents. Eighty-two percent of the 3,113 birds that were cleaned died prior to or at time of release. The fate of the remaining 18% is unknown. Petroleum solvents used as cleaning agents were toxic to the birds. Most detergents left a surfactant (wetting agent) on the feathers which resulted in subsequent wetting of released birds. Although rehabilitation techniques have improved in recent years, high bird mortality can be expected following future oil spills.

Chesapeake Bay, Delaware River↗
USGS1997

Mercury concentrations in feathers of wading birds from Florida

Primary or tail feathers were collected from 92 wading birds in Florida from Lake Okeechobee and wetlands farther south, from 1987 to 1990. Mean concentrations detected in feathers of nestlings were 2.0 ppm Hg in roseate spoonbills (Ajaia ajaja), 3.5 ppm Hg in great blue herons (Ardea herodias), 4.7 ppm Hg in great white herons (Ardea herodias occidentalis), and 7.1 ppm Hg in great egrets (Casmerodius albus). Concentrations in feathers of great white herons increased with the age of the bird, from 4.7 ppm Hg in nestlings, to 6.7 ppm Hg in juveniles, and 8.2 ppm Hg in adults. Mercury concentrations were greatest in species consuming large fish. Feathers collected from wood storks (Mycteria americana) contained an average of 3.3 ppm Hg. Mercury concentrations in feathers of wading birds from southern Florida were greater than those reported in feathers of wading birds from Asia. Both liver and feather Hg concentrations were known for 25 wading birds. The regression of liver (wet weight) Hg concentrations (Y) on feather Hg concentrations (X) was: log(Y) = 1.52 log(X) - 0.722. The correlation coefficient was 0.84. If reproductive disorders are expected when concentrations in feathers of adult birds average 9 ppm Hg, as might be inferred from a published laboratory study on mallards (Anas platyrhynchos), then Hg in southern Florida may be high enough to reduce productivity of wading bird populations. However, additional controlled studies are needed before a minimum toxic concentration in feathers can be designated with confidence.

Ambio↗
USGS1995

Residues and trends of organochlorine pesticide and polychlorinated biphenyls in birds from Texas, 1965-88

Concentrations of DDE (a metabolite of DDT) in birds decreased during recent years in most areas of the continental United States. Organochlorine pesticides were widely used in agriculture in Texas from the early 1950s to the 1970s. I used previously published data to determine whether concentrations of DDE and polychlorinated biphenyls (PCBs) in birds from Texas have followed a decreasing trend similar to that in birds from other areas in the United States. A total of 2,669 bird samples was collected between 1965 and 1988 from diverse locations in Texas and was analyzed for organochlorines and other environmental contaminants. The brown pelican ( Pelecanus occidentalis ), peregrine falcon ( Falco peregrinus ), laughing gull ( Larus atricilla ), black skimmer ( Rynchops niger ), and European starling ( Sturnus vulgaris ) were the most frequently studied species. DDE and PCBs were the most commonly detected organochlorines in bird tissues. Mean DDE concentrations ranged from 0.4 to 61.00 parts per million (ppm) wet weight (ww) and PCBs from 0.02 to 32.00 ppm ww. Concentrations of DDE in eggs and carcasses of black skimmers decreased significantly during 1970-84 and dropped from approximately 10 to nearly 3 ppm ww. PCBs decreased from approximately 7 ppm ww to 1 ppm ww in eggs and carcasses. DDE concentrations in eggs of brown pelicans varied from more than 3 ppm ww in 1970 to approximately 1 ppm ww in 1983; and PCB concentrations diminished from about 10 to 1 ppm ww. Decreasing trends in concentrations of DDE and PBCs were observed in most species, although in some cases, the estimated trends were not significantly different from zero. Concentrations of DDE in birds from the Texas coast decreased from more than 6.0 ppm in 1978 to below 0.5 ppm in 1985. The decreasing ratios in selected species varied from approximately 2.0 to 12.0 (DDE) and from 4.5 to 9.0 (PCBs). The results indicate that in general from 1965 to 1988, DDE and PCBs declined in birds from Texas.

Texas↗