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At least 19 recordsLinked to original sources
USGS2015

Science foundation Chapter 5 Appendix 5.1: Case study shore birds: Western sandpipers ( Calidris mauri ) and American avocets ( Recurvirostra Americana )

Western sandpipers ( Calidris mauri ) are small (22-35 g) sexually dimorphic sandpipers, with males typically smaller than females. Western sandpipers frequently occur in mixed species flocks along with other Calidris species, including least sandpipers ( Calidris minutilla ) and dunlin ( Calidris alpina ), in the San Francisco Bay Estuary (SFBE) and are the most abundant shorebird species found from fall to spring. Western sandpipers are one of the most common shorebird species in SFBE, the Pacific Flyway, and North America overall. The largest concentrations of western sandpipers, and of most shorebirds, are found in the South Bay where large expanses of mudflats are exposed at low tide and managed and/or salt ponds are available for high tide roosting and feeding habitat (Warnock et al 2002, Warnock and Takekawa 1995). In recent years, there is some evidence that there has been a shift in shorebird numbers towards the North Bay, perhaps as large salt pond restoration projects provide interim mud flat habitat during the evolution towards tidal marsh habitat (Pitkin and Wood, 2011).

California↗
USGS2017

Trends and traditions: Overview and synthesis

This paper provides an overview by the editors of a collection of 25 papers for the Studies of Western Birds, to be published in a single volume by Western Field Ornithologists. The title of the volume is: "Trends and traditions: Avifaunal change in western North America."

Book chapter↗
USGS2012

Modelling effects of chemical exposure on birds wintering in agricultural landscapes: The western burrowing owl ( Athene cunicularia hypugaea ) as a case study

We describe an ecotoxicological model that simulates the sublethal and lethal effects of chronic, low-level, chemical exposure on birds wintering in agricultural landscapes. Previous models estimating the impact on wildlife of chemicals used in agro-ecosystems typically have not included the variety of pathways, including both dermal and oral, by which individuals are exposed. The present model contains four submodels simulating (1) foraging behavior of individual birds, (2) chemical applications to crops, (3) transfers of chemicals among soil, insects, and small mammals, and (4) transfers of chemicals to birds via ingestion and dermal exposure. We demonstrate use of the model by simulating the impacts of a variety of commonly used herbicides, insecticides, growth regulators, and defoliants on western burrowing owls ( Athene cunicularia hypugaea ) that winter in agricultural landscapes in southern Texas, United States. The model generated reasonable movement patterns for each chemical through soil, water, insects, and rodents, as well as into the owl via consumption and dermal absorption. Sensitivity analysis suggested model predictions were sensitive to uncertainty associated with estimates of chemical half-lives in birds, soil, and prey, sensitive to parameters associated with estimating dermal exposure, and relatively insensitive to uncertainty associated with details of chemical application procedures (timing of application, amount of drift). Nonetheless, the general trends in chemical accumulations and the relative impacts of the various chemicals were robust to these parameter changes. Simulation results suggested that insecticides posed a greater potential risk to owls of both sublethal and lethal effects than do herbicides, defoliants, and growth regulators under crop scenarios typical of southern Texas, and that use of multiple indicators, or endpoints provided a more accurate assessment of risk due to agricultural chemical exposure. The model should prove useful in helping prioritize the chemicals and transfer pathways targeted in future studies and also, as these new data become available, in assessing the relative danger to other birds of exposure to different types of agricultural chemicals.

Texas↗
USGS2017

Changes in the abundance and distribution of waterfowl wintering in the Central Valley of California, 1973–2000

The Central Valley of California is one of the most important areas for wintering waterfowl in the world and the focus of extensive conservation efforts to mitigate for historical losses and counter continuing stressors to habitats. To guide conservation, we analyzed trends in the abundance and distribution (spatiotemporal abundance patterns) of waterfowl and their habitats in the Central Valley and its major subregions (Sacramento Valley, Suisun Marsh, Delta, San Joaquin Valley), from 1973 through 2000. We used existing databases, satellite imagery, and aerial photography to measure habitat area, and aerial surveys and radio telemetry to track the abundance and distribution of wintering waterfowl. Wetlands increased throughout the Central Valley, but agricultural fields flooded after harvest increased greatly to the north in the Sacramento Valley and decreased to the south in the San Joaquin Valley, resulting in an overall increase in the relative availability of winter habitat in the former region. Reflecting the continental decline of the most abundant wintering species (Northern Pintail, Anas acuta ), the overall abundance of wintering waterfowl in the Central Valley declined during our study. By contrast, numbers of the American Wigeon ( A. americana ), Mallard ( A. platyrhynchos ), and Northern Shoveler ( A. clypeata ) were stable, and numbers of the Green-winged Teal ( A. crecca ), Gadwall ( A. strepera ), diving ducks, and geese increased from 1973–1982 to 1998–2000. The areas of greatest abundance of wintering waterfowl within the Central Valley shifted northward as many species responded to changes in the distribution of habitats. Wintering waterfowl migrated earlier in fall and winter from the San Joaquin Valley, Suisun Marsh, and Delta to the Sacramento Valley, and fewer waterfowl emigrated from the Sacramento Valley to other parts of the Central Valley. Because changes in waterfowl distribution were primarily a response to the increase of a beneficial agricultural practice (i.e., the flooding of rice after harvest) in the Sacramento Valley, changing agro-economics, reduction of water supplies, or other factors that reduce this practice could change the abundance and distribution of wintering waterfowl in the Central Valley rapidly. Thus to maintain abundant suitable habitat and restore the historical distribution of wintering waterfowl, our results suggest a continuing need for the conservation of wetlands and other waterfowl habitats with secure water supplies throughout the Central Valley. Despite our findings, achieving goals for winter waterfowl populations in the Central Valley likely will depend on a combination of factors including some acting in breeding ranges farther north or elsewhere outside of the valley.

California↗
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↗
USGS2004

Migration stopover ecology of western avian populations: A southwestern migration workshop

The importance of migration stopover sites in ensuring that migratory birds successfully accomplish their journeys between breeding and non-breeding ranges has come to the forefront of avian research. Migratory birds that breed in western United States (US) and Canada and overwinter primarily in western Mexico migrate across the arid region of northern Mexico and southwestern US. Many of these migrants use lowland riparian stopover habitats, which comprise less than 0.1% of the western U.S. landscape. These habitats represent a significant conservation priority. Recognizing the importance of migration stopover habitats in the arid southwest, the U.S. Fish and Wildlife Service (USFWS) Region 6 partnered with the U.S. Geological Survey (USGS) to support a project---“Migration stopover ecology of western avian populations: patterns of geographic and habitat distribution.” A primary objective of the project was to convene a workshop for avian researchers, conservation professionals, and land managers involved in stopover needs of migratory birds that breed in western North America. The workshop included presentations on our current state of knowledge regarding passerine migration in western North America, techniques and technologies potentially useful in researching migration, and efforts that agencies and other partners are conducting within the realm of migration. Workshop presentations provided a backdrop for subsequent discussions, the goals of which were to identify research needs and initiate a coordinated approach to research of western migration stopover ecology. Workshop presentations spanned a wide range of concerns and interests. Highlights included indications that mid- and high-elevation riparian and montane shrubland habitats may be as crucial to western migrants in fall migration as lowland riparian habitats are in spring migration. Comparisons of eastern versus western migration systems elucidated large differences in stopover habitats used and the intensity with which certain types are used, underscoring the potential need to develop separate management approaches for eastern and western stopover sites. Presentations on techniques and technology for migration research revealed that rate of lipid deposition can serve as an indicator of habitat quality; that genetics and stable isotope analyses of feathers can be valuable tools to elucidate linkages between breeding and wintering areas; that radar imagery can be used to track large-scale movement patterns and habitat use; and that there are analytical options for combining multiple sources of information. Other presentations focused on partnership perspectives (USFWS and Sonoran Joint Venture), the genesis of a western migration monitoring network, premises of Coordinated Bird Monitoring, and how collaborative efforts could benefit migration research (e.g., combined bird and bat migration studies; linking avian researchers with fluvial geomorphologists; linking research throughout western North America; linking surveys and banding). Priority research needs and questions identified during the open discussions fell into three main categories: (1) habitat/landscape/climate relationships, (2) en route bird distribution patterns, and (3) general migration ecology. Tasks within these categories included: define the relative importance of various habitat types to migrants in spring and fall, determine what distinguishes high- from poor-quality stopover habitat; determine geographic patterns of loss in stopover habitats; model landscape attributes associated with species richness and abundance; identify effects of climate change and current climate anomalies on plant phonologies, associated insect flushes, and timing of migration; and determine effects of hydrologic changes on riparian vegetation, food availability, and stopover habitat quality. Workshop participants discussed a coordinated approach for addressing immediate research needs regarding migration patterns and crucial stopover sites and types. They envisioned a three­-tiered, coordinated approach: (1) long-term research to address effects of climate change and other large-scale patterns, (2) intensive, short-term survey and monitoring efforts using a stratified random design within habitats of interest to elucidate regional patterns of distribution and habitat use, and (3) research conducted at existing survey and banding sites to address more in-depth questions (e.g., rates of lipid deposition, microhabitat use, isotope analyses). There was considerable interest in developing common research proposals to blend the broad expertise represented at this workshop. A second meeting is recommended to build on the momentum of these discussions, to facilitate collaborations, and further the goals of integrated approaches to broadscale research on migration stopover ecology.

Open-File Report↗
USGS2002

Genetic parentage and mate guarding in the Arctic-breedng Western Sandpiper

Extrapair copulations and fertilizations are common among birds, especially in passerines. So far, however, few studies have examined genetic mating systems in socially monogamous shorebirds. Here, we examine parentage in the Western Sandpiper ( Calidris mauri ). Given that Western Sandpipers nest at high densities on the Arctic tundra, have separate nesting and feeding areas, and show high divorce rates between years, we expected extrapair paternity to be more common in this species compared to other monogamous shorebirds. However, DNA fingerprinting of 98 chicks from 40 families revealed that only 8% of broods contained young sired by extrapair males, and that 5% of all chicks were extrapair. All chicks were the genetic offspring of their social mothers. We found that males followed females more often than the reverse. Also, cuckolded males were separated from their mates for longer than those that did not lose paternity. Although these results suggest a role for male mate guarding, we propose that high potential costs in terms of reduced paternal care likely constrain female Western Sandpipers from seeking extrapair copulations.

The Auk↗
USGS1984

Breeding bird community colonization of sown stands of native grasses in North Dakota

Breeding passerine birds were studied in three native grass plantings of predominantly western wheatgrass (Agropyron smithii) and green needlegrass (Stipa viridula) in south-central North Dakota during 1982-1984. A total of eight different species of passerines readily colonized this relatively new type of wildlife habitat during the second, third. and fourth growing seasons.

Prairie Naturalist↗
USGS2011

A puzzling migratory detour : Are fueling conditions in Alaska driving the movement of juvenile sharp -tailed sandpipers ?

Making a detour can be advantageous to a migrating bird if fuel-deposition rates at stopover sites along the detour are considerably higher than at stopover sites along a more direct route. One example of an extensive migratory detour is that of the Sharp-tailed Sandpiper ( Calidris acuminata ), of which large numbers of juveniles are found during fall migration in western Alaska. These birds take a detour of 1500–3400 km from the most direct route between their natal range in northeastern Siberia and nonbreeding areas in Australia. We studied the autumnal fueling rates and fuel loads of 357 Sharp-tailed Sandpipers captured in western Alaska. In early September the birds increased in mass at a rate of only 0.5% of lean body mass day -1 . Later in September, the rate of mass increase was about 6% of lean body mass day -1 , among the highest values found among similar-sized shorebirds around the world. Some individuals more than doubled their body mass because of fuel deposition, allowing nonstop flight of between 7100 and 9800 km, presumably including a trans-oceanic flight to the southern hemisphere. Our observations indicated that predator attacks were rare in our study area, adding another potential benefit of the detour. We conclude that the most likely reason for the Alaskan detour is that it allows juvenile Sharp-tailed Sandpipers to put on large fuel stores at exceptionally high rates.

Alaska↗
USGS2008

Organochlorine pollutants and stable isotopes in resident and migrant passerine birds from northwest Michoacán, Mexico

Although concentrations of organochlorine compounds (OCs) in birds from most of the United States and Canada have decreased over the last 30 years, there is still concern that migrant birds might be exposed to elevated concentrations of OCs during migration in Latin America. The Lerma-Chapala Basin in west-central Mexico is an important migration corridor and wintering area for many species. The objectives of this study were to assess if resident and migrant birds wintering in western Michoacán, Mexico accumulated elevated concentrations of OCs during fall and spring and to determine if the stable isotopes δ 15 N, δ 13 C, and δD could be used to predict burdens and origins of DDE accumulation. Resident and migrant passerine insectivorous birds were collected during fall and spring (2001–2002) in northwest Michoacán, near Chapala Lake, Mexico. The carcasses were analyzed for OCs and tail feathers were analyzed for stable isotopes δ 15 N, δ 13 C, and δD. The OCs detected in more than 50% of the samples were: oxychlordane (79%), p,p ’-DDE (100%), p ,p′-DDT (57%), and total PCBs (100%). p,p ′-DDE was the OC detected at the highest concentrations, whereas residues of other OCs were near or below detection limits. Overall, there were no significant differences in concentrations of OCs between seasons or between resident and migrant birds. Concentrations of DDE and oxychlordane were somewhat higher in migrant and resident birds during spring than in fall; however, concentrations were significantly different only for oxychlordane. Two resident birds collected in fall and spring had DDE residues >10 μg/g wet weight in carcass. There were no significant differences in δ 13 C and δ 15 N values among species, between seasons, or between migrant and resident birds. However, δD values were clearly different between species and helped differentiate migrant from resident birds. δD values also were negatively and significantly correlated with DDE concentrations in carcass. Birds with more depleted δD values in feathers tended to have higher DDE concentrations than those with less depleted δD values, suggesting a potential latitudinal accumulation of DDE. Overall, our results suggest that during fall and spring, there is not a significant buildup of persistent OCs in migrant and resident passerine insectivorous birds in northwest Michoacán, Mexico.

Michoacán↗
USGS2002

Space use, migratory connectivity, and population segregation among Willets breeding in the western Great Basin

Western Willets ( Catoptrophorus semipalmatus inornatus ) were banded (n = 146 breeding adults and chicks) and radio-marked (n = 68 adults) at three western Great Basin wetland complexes to determine inter- and intraseasonal space use and movement patterns (primarily in 1998 and 1999). Birds were then tracked to overwintering sites where migratory connectivity and local movements were documented. Willets arrived synchronously at breeding sites during mid-April and spent less than 12 weeks in the Great Basin. There were no movements to other sites in the Great Basin during the breeding or postbreeding season. However, most breeding birds moved locally on a daily basis from upland nest sites to wetland foraging sites. The mean distance breeding birds were detected from nests did not differ between sexes or between members of a pair, although these distances were greater among postbreeding than breeding birds. Home-range estimates did not differ significantly between paired males and females during breeding or postbreeding. However, female home ranges were larger following breeding than during breeding. Shortly after chicks fledged, adult Willets left the Great Basin for locations primarily at coastal and estuarine sites in the San Francisco Bay area. Limited data revealed little among-site movements once Willets arrived at the coast, and birds appeared to be site faithful in subsequent winters. Winter sites of western Great Basin Willets differed from those used by birds from other areas in the subspecies' range, suggesting another subspecies or distinct population segment may exist. This study illustrates the importance of understanding movements and space use throughout the annual cycle in conservation planning.

California, Oregon↗
USGS2009

Scrub-shrub bird habitat associations at multiple spatial scales in beaver meadows in Massachusetts

Most scrub-shrub bird species are declining in the northeastern United States, and these declines are largely attributed to regional declines in habitat availability. American Beaver ( Castor canadensis ; hereafter “beaver”) populations have been increasing in the Northeast in recent decades, and beavers create scrub-shrub habitat through their dam-building and foraging activities. Few systematic studies have been conducted on the value of beaver-modified habitats for scrub-shrub birds, and these data are important for understanding habitat selection of scrub-shrub birds as well as for assessing regional habitat availability for these species. We conducted surveys in 37 beaver meadows in a 2,800-km 2 study area in western Massachusetts during 2005 and 2006 to determine the extent to which these beaver-modified habitats are used by scrub-shrub birds, as well as the characteristics of beaver meadows most closely related to bird use. We modeled bird abundance in relation to microhabitat-, patch-, and landscape-context variables while adjusting for survey-specific covariates affecting detectability using N-mixture models. We found that scrub-shrub birds of regional conservation concern occupied these sites and that birds responded differently to microhabitat, patch, and landscape characteristics of beaver meadows. Generally, scrub-shrub birds increased in abundance along a gradient of increasing vegetation complexity, and three species were positively related to patch size. We conclude that these habitats can potentially play an important role in regional conservation of scrub-shrub birds and recommend that conservation priority be given to larger beaver meadows with diverse vegetation structure and composition.

Massachusetts↗
USGS2012

One year of migration data for a western yellow-billed cuckoo

In 2009, we studied the migration of the Western Yellow-billed Cuckoo by capturing 13 breeding birds on the middle Rio Grande, New Mexico, and attaching a 1.5-g Mk 14-S British Antarctic Survey geolocator to each bird. In 2010, we recaptured one of the cuckoos, enabling us to download its geolocation data. The cuckoo had flown approximately 9500 km during its southward migration, traveling through Central America to winter in portions of Bolivia, Brazil, Paraguay, and Argentina. The spring migration route differed somewhat from the fall route, with the cuckoo bypassing Central America to migrate through the Caribbean. Additionally, it moved between New Mexico and Mexico at the end of summer in 2009 and again in 2010 before being recaptured at its breeding site. Our results, albeit from one individual, hint at a dynamic migration strategy and have broad implications for the ecology and conservation of the Western Yellow-billed Cuckoo, a species of conservation concern.

Western Birds↗
USGS2004

Factors influencing occupancy of nest cavities in recently burned forests

Recently burned forests in western North America provide nesting habitat for many species of cavity-nesting birds. However, little is understood about the time frame and the variables affecting occupancy of postfire habitats by these birds. We studied factors influencing the occupancy and reuse of nest cavities from 1-7 years after fire in two burned sites of western Idaho during 1994-1999. Tree cavities were used for nesting by 12 species of cavity nesters that were classified by the original occupant (strong excavator, weak excavator, or nonexcavator) of 385 nest cavities. We used logistic regression to model cavity occupancy by strong excavators (n = 575 trials) and weak excavators (n = 206 trials). Year after fire had the greatest influence on occupancy of nest cavities for both groups, while site of the burn was secondarily important in predicting occupancy by strong excavators and less important for weak excavators. Predicted probability of cavity occupancy was highest during the early years (1-4) after fire, declined over time (5-7 years after fire), and varied by site, with a faster decline in the smaller burned site with a greater mosaic of unburned forest. Closer proximity and greater interspersion of unburned forest (15% unburned) may have allowed a quicker recolonization by nest predators into the smaller burn compared to the larger burn with few patches of unburned forest (4% unburned). In combination with time and space effects, the predicted probability of cavity occupancy was positively affected by tree and nest heights for strong and weak excavators, respectively.

Conference Paper↗
USGS1983

Impacts of forest herbicides on wildlife: Toxicity and habitat alteration

This paper begins with a review of both laboratory and field studies on tbe possible direct toxic effects of herbicides on terrestrial vertebrates, primarily birds and mammals. Alteration of the palatability of forage and changes in reproductive success are also discussed. Emphasis is placed on the use of herbicides in forestry; studies dealing with agricultural systems are referenced where appropriate. The indirect effects of herbicides on wildlife-habitat are then conceptualized and quantified using data from a 3-year study on effects of phenoxy and glyphosate herbicides on bird and small mammal communities in western Oregon. Data on density and habitat use are presented and compared with data available from other geographic regions.

Transactions of the North American Wildlife and Na↗
USGS2014

Associations of wintering birds with habitat in semidesert and plains grasslands in Arizona

We studied associations with winter habitat for seven species of birds, one species-group (eastern and western meadowlarks combined), and total sparrows at seven sites in the semidesert and plains grasslands of southeastern Arizona from 1999–2001, sampling with mist-nets and survey-transects. We measured structure and composition of vegetation, assessing vegetative differences among sites, and modeled associations between indices of avian abundance and six vegetative variables using generalized linear models. For all vegetative variables, there were significant differences among sites. Numbers of northern harriers ( Circus cyaneus ) were positively associated with total number of sparrows. Indices of abundance for individual species of birds were statistically correlated with various measures of structure and composition of vegetation. In particular, grasshopper ( Ammodramus savannarum ) and vesper ( Pooecetes gramineus ) sparrows were negatively associated with amount of bare ground; horned larks ( Eremophila alpestris ) were negatively associated with vertical grass density; Baird's sparrows ( A. bairdii ) were negatively associated with shrub density; meadowlarks ( Sturnella magna and S. neglecta combined) were positively associated with native grass. Our results suggest that these species would benefit from management of habitat that affects the vegetative characteristics associated with their abundance.

Arizona↗
USGS2008

Low prevalence of avian influenza virus in shorebirds on the Pacific coast of North America

The emergence of highly pathogenic avian influenza (HPAI) H5N1 has elevated concerns about wild birds as virus hosts; however, little is known about the ecological and epidemiological factors of transmission by shorebirds. Here we summarize results for 2,773 shorebirds that were live-trapped on the Pacific coast of the United States during 2006-2007 and tested for avian influenza virus using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and virus isolation. As was the case throughout North America, HPAI H5N1 was not detected in shorebirds during this interval. Contrary to other wild bird groups, most notably waterfowl, the prevalence of even low pathogenicity virus among shorebirds in our study areas in California, Washington, and Alaska was extremely low (0.5%). Virus was detected by RT-PCR from four different species, including, Dunlin (Calidris alpina; N = 3), Western Sandpiper (C. mauri; N = 8), Long-billed Dowitcher (Limnodromus scolopaceus; N = 1), and American Avocet (Recurvirostra americana; N = 1), with the detections in the latter three constituting the first published records for these birds. Based on studies in the eastern United States, we expected, but did not detect (H 1 = 1.6, P = 0.21) elevated avian influenza prevalence among shorebirds during spring migration. Diagnostic tests, which were designed to evaluate testing and sampling methods, indicated poor functioning of traditional virus isolation methods and no improvement in detection likelihood by collecting oropharyngeal swabs in addition to cloacal swab samples for low pathogenicity viruses (Z 1 = 0.7, P = 0.48).

Waterbirds↗
USGS2007

Status review of the Marbled Murrelet (Brachyramphus marmoratus) in Alaska and British Columbia

The Marbled Murrelet ( Brachyramphus marmoratus ) is a small, diving seabird inhabiting inshore waters of the Northeastern Pacific Ocean. This species feeds on small, schooling fishes and zooplankton, and nests primarily on the moss-covered branches of large, old-growth conifers, and also, in some parts of its range, on the ground. We reviewed existing information on this species to evaluate its current status in the northern part of its range—Alaska (U.S.) and British Columbia (Canada). Within the southern part of its range (Washington, Oregon, and California, U.S.), the Marbled Murrelet was listed as a threatened species under the Endangered Species Act (ESA) in 1993, and the U.S. Fish and Wildlife Service (USFWS) needed information on the species throughout its range for ESA deliberations. We compiled published information on the conservation status, population biology, foraging ecology, population genetics, population status and trends, demography, marine and nesting habitat characteristics, threats, and ongoing conservation efforts for Marbled Murrelets in Alaska and British Columbia. We conducted a new genetic study using samples from a segment of the range that had not been included in previous studies (Washington, Oregon) and additional nuclear intron and microsatellite markers. We also analyzed available at-sea survey data from several locations for trend. To understand the reasonableness of the empirical trend data, we developed demographic models incorporating stochasticity to discern what population trends were possible by chance. The genetic studies substantially confirmed previous findings on population structure in the Marbled Murrelet. Our present work finds three populations: (1) one comprising birds in the central and western Aleutian Islands; (2) one comprising birds in central California; and (3) one comprising birds within the center of the range from the eastern Aleutians to northern California. Our knowledge of genetic structure within this central population is limited and it requires additional study. Compiling available abundance information, we estimated that in the recent past, Marbled Murrelets in Alaska numbered on the order of 1 million birds. We were unable to generate a similar estimate for historical population size in British Columbia. Using trend information from at-sea surveys spanning a wide geographic range in Alaska, murrelet numbers declined significantly at five of eight trend sites at annual rates of -5.4 to -12.7 percent since the early 1990s. Applying these rates of decline to the historical population estimate, the current murrelet population in Alaska is projected to be on the order of 270,000 birds. This represents an overall population decline of about 70 percent during the past 25 years. In British Columbia, available trend data indicate that murrelet populations there have experienced similar declines. We updated a recent (2002) population estimate for British Columbia, concluding that there are now between 54,000 and 92,000 murrelets in British Columbia. The rates of decline we observed are within, but at the high end of, a range of rates expected by chance. Given that declines were estimated for sites over essentially the entire northern range of the species, there is cause for concern about the species’ status. In their marine habitats, Marbled Murrelets overlap with salmon (Oncorhynchus sp.) gillnetting operations in British Columbia and in Alaska (especially in Prince William Sound and Southeast Alaska), and annual bycatch mortality is likely in the low thousands per year, although bycatch rates are difficult to measure. The species’ inshore distribution coincides with high levels of vessel traffic and makes them especially vulnerable to both chronic oil pollution and to catastrophic spills (e.g., the 1989 Exxon Valdez oil spill [EVOS] in south-central Alaska, which is estimated to have killed 12,000 to 15,000 murrelets). In their forested nesting habitats, Marbled Murrelets have lost about 15 percent of their suitable nesting habitat in Southeast Alaska, and 33 to 49 percent in British Columbia, from industrial-scale logging within the past half century. Increased predation also may be a threat to murrelet populations, related to fragmentation and edge effects from logging and development, and recent population increases observed for some important murrelet predators, including Bald Eagles ( Haliaeetus leucocephalus ), Common Ravens ( Corvus corax ), and Steller’s Jays ( Cyanocitta stelleri ). Nesting habitat losses cannot explain the declines observed in areas where industrial logging has not occurred on a large scale (e.g., Prince William Sound) or at all (Glacier Bay). The apparent change in population size and rates of decline reported for the Marbled Murrelet are large, and we therefore considered alternative explanations and precedents for changes of similar magnitude in other marine wildlife populations in the Northeastern Pacific Ocean. The declines are likely real, and related to combined and cumulative effects from climate-related changes in the marine ecosystem (most likely the 1977 regime shift) and human activities (logging, gillnet bycatch, oil pollution). Much uncertainty about the decline could be alleviated by continuing to repeat boat surveys in Prince William Sound and lower Cook Inlet, and by repeating the boat survey of Southeast Alaska that was conducted in 1994. This survey used a statistically sound design and covered the region that has been and likely remains the center of the species’ abundance. Important questions remain to be addressed about methods for measuring population status and change, adult mortality (major sources, density dependence, seasonal concordance), and the movements of wintering populations.

Alaska, British Columbia↗