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USGS2007

Arthropod prey of Wilson's Warblers in the understory of Douglas-fir forests

Availability of food resources is an important factor in avian habitat selection. Food resources for terrestrial birds often are closely related to vegetation structure and composition. Identification of plant species important in supporting food resources may facilitate vegetation management to achieve objectives for providing bird habitat. We used fecal analysis to describe the diet of adult Wilson's Warblers ( Wilsonia pusilla ) that foraged in the understory of Douglas-fir ( Pseudotsuga menziesii ) forests in western Oregon during the breeding season. We sampled arthropods at the same sites where diet data were collected, and compared abundance and biomass of prey among seven common shrub species. Wilson's Warblers ate more caterpillars (Lepidoptera larvae), flies (Diptera), beetles (Coleoptera), and Homoptera than expected based on availability. Deciduous shrubs supported higher abundances of arthropod taxa and size classes used as prey by Wilson's Warblers than did evergreen shrubs. The development and maintenance of deciduous understory vegetation in conifer forests of the Pacific Northwest may be fundamental for conservation of food webs that support breeding Wilson's Warblers and other shrub-associated, insectivorous songbirds.

Oregon↗

USGS1994

Bioaccumulation of selenium from natural geologic sources in western states and its potential consequences

Ecological impacts of water-quality problems have developed in the western United States resulting from the disposal of seleniferous agricultural wastewater in wetland areas. Overt effects of selenium toxicosis occurred at five areas where deformities of wild aquatic birds were similar to those first observed at Kesterson National Wildlife Refuge in the west-central San Joaquin Valley of California. These areas are: Tulare Lake Bed Area, California, Middle Green River Basin, Utah, Kandrick Reclamation Project Area, Wyoming, Sun River Basin, Montana, and Stillwater Wildlife Management Area, Nevada. Potential for ecological damage is indicated at six more sites in Oregon, Colorado, the Colorado/Kansas border, and South Dakota out of 16 areas in 11 states where biological tissue data were collected. This conclusion is based on the fact that selenium bioaccumulated in bird livers to median levels that had exceeded or were in the range associated with adverse reproductive effects. Selenium concentrations in samples of fish and bird eggs support these conclusions at a majority of these areas. Reason for concern is also given for the lower Colorado River Valley, although this is not exclusively a conclusion from these reconnaissance data. Biogeochemical conditions and the extent of selenium contamination of water, bottom sediment, and biota from which this assessment was made are given here. In a companion paper, the biogeochemical pathway postulated for selenium contamination to take place from natural geologic sources to aquatic wildlife is defined.

Environmental Management↗

USGS1995

Population size, trends, and conservation problems of the Double-Crested Cormorant on the Pacific Coast of North America

Population size, trends and conservation problems of the Double-crested Cormorant ( Phalacrocorax auritus ) were collated for the Pacific coast of North America using available data up to 1992. About 54,942 birds currently breed there, including roughly 5,848 (5,622 at 90 coastal colonies and at least 226 at 5 interior colonies) and 49,094 (43,358 at 126 coastal colonies and at least 5,736 at 22 interior colonies) for subspecies P. a. cincinatus in Alaska and P. a. albociliatus , from British Columbia to Sinaloa (Mexico), respectively. In addition, 51 and 22 inactive colonies have been documented in coastal and interior regions, respectively. Major historical declines (in the 1800s and early 1900s) occurred in much of Alaska, California, and Mexico, followed by increases in British Columbia, Washington, Oregon and California from the 1920s to 1980s. Recent declines are occurring in British Columbia, Washington, and Baja California. Trends are affected by apparent movements of nesting birds during El Niño oceanographic conditions and due to habitat loss at interior colonies, as well as recent use of artificial nesting habitats in some areas. Conservation problems have included various forms of human disturbance and persecution, marine pollutants, and high levels of predation owing to introduced and natural predators.

Alaska, California, Oregon, Washington↗

USGS1983

Pacific Coast Caspian Terns: Dynamics of an expanding population

Nesting distribution, age-related seasonal movements, survivorship, and mechanisms of population expansion in Pacific Coast Caspian Terns (Sterna caspia) were examined primarily through analysis of 412 recoveries of birds banded as juveniles between 1935 and 1980. Since the beginning of this century, the population has shifted from nesting in numerous small colonies associated with freshwater marshes in interior California and southern Oregon to nesting primarily in large colonies on human-created habitats along the coast. Colonies at Grays Harbor, Washington and San Francisco and San Diego bays, California account for 77% of the current Pacific Coast population (6,000 pairs), which has breeding and wintering areas separate from those of populations east of the continental divide. There also appears to be some segregation on the wintering grounds by birds from the three major colonies within the Pacific population. Age-related seasonal movements in the Pacific population are characterized by (1) a brief period of northward dispersal by newly fledged birds before migrating to the wintering grounds, (2) a residency on the wintering grounds through their second winter, (3) a return to the breeding grounds the third summer, when most birds are thought to prospect breeding sites and some may breed, and (4) attainment of adulthood the fourth summer, with subsequent annual movements between wintering and breeding grounds. The Pacific population has increased 70% since 1960, apparently all by intrinsic growth. Over half (57%) of the fledglings reach their fourth year, and they have a subsequent annual survival rate of 89% and a mean breeding life expectancy of 8.6 yr. An average annual fledging rate of 0.64 young per pair was calculated as necessary to have provided the observed growth of the population during its recent expansion. Growth of some of the individual colonies, however, particularly those in Washington, could only have resulted from extensive recruitment of birds from other Pacific Coast colonies. Philopatry is low in this population, and the growth of the northern colonies involved recruitment primarily of first-time breeders but also of some older adults. Factors promoting both first-time breeders and older adults to join new and often distant colonies are discussed.

California, Washington↗

USGS2014

Interspecific nest parasitism by chukar on greater sage-grouse

Nest parasitism occurs when a female bird lays eggs in the nest of another and the host incubates the eggs and may provide some form of parental care for the offspring (Lyon and Eadie 1991). Precocial birds (e.g., Galliformes and Anseriformes) are typically facultative nest parasites of both their own and other species (Lyon and Eadie 1991). This behavior increases a female’s reproductive success when she parasitizes other nests while simultaneously raising her own offspring. Both interspecific and conspecific nest parasitism have been well documented in several families of the order Galliformes, particularly the Phasianidae (Lyon and Eadie 1991, Geffen and Yom-Tov 2001, Krakauer and Kimball 2009). The Chukar (Alectoris chukar) has been widely introduced as a game bird to western North America from Eurasia and is now well established within the Great Basin from northeastern California east to Utah and north to Idaho and Oregon (Christensen 1996). Over much of this range the Chukar occurs with other phasianids, including the native Greater Sage-Grouse (Centrocercus urophasianus), within sagebrush (Artemisia spp.) steppe (Christensen 1996, Schroeder et al. 1999, Connelly et al. 2000). Chukar typically exploit a broader range of habitats than do sage-grouse, but both species use the same species of sagebrush and other shrubs for nesting cover (Christensen 1996, Schroeder et al. 1999). Chukar are known to parasitize nests of other individuals of their own species (Geffen and Yom-Tov 2001), but we are unaware of reported evidence that Chukar may parasitize nests of sage-grouse. Here we describe a case of a Chukar parasitizing a sage-grouse nest in the sagebrush steppe of western Nevada.

Western Birds↗

USGS2001

Biology and conservation of the common murre in California, Oregon, Washington, and British Columbia: Vol. 1, Natural history and population trends

Over the past 30 years, the common murre ( Uria aalge californica ) has been recognized as a prominent indicator of marine conservation issues in California, Oregon, Washington, and British Columbia, especially regarding oil pollution, certain fisheries, and human disturbance. To assist the effective management of the common murre and the marine environments in which they live, this summary of available information on the biology and regional status of the common murre has been sponsored by the U.S. Fish and Wildlife Service (Division of Migratory Bird Management). In Volume 1 (Chapter 1), the natural history of the common murre is summarized, drawing heavily on breeding studies from the South Farallon Islands, California, plus a host of detailed breeding studies from the North Atlantic Ocean. Population trends of the common murre are summarized in Volume 1 (Chapter 2), focusing on changes in whole-colony counts determined from aerial photographs between the late 1970s and 1995 in California, Oregon and Washington. Historical data and human impacts to murre colonies since the early nineteenth century are also summarized. Volume 2 will summarize population threats, conservation, and management. Information presented in Volume 1 has been obtained and recorded by a large number of researchers and natural historians over two centuries. From the 1960s to 1995, most work in California, Oregon, and Washington was sponsored by the U.S. Fish and Wildlife Service, Minerals Management Service, and California Department of Fish and Game. Important breeding biology studies were conducted at the South Farallon Islands (Farallon National Wildlife Refuge) by the Point Reyes Bird Observatory, in coordination with the U.S. Fish and Wildlife Service (San Francisco Bay National Wildlife Refuge). Colony surveys in California were conducted mainly by the U.S. Fish and Wildlife Service (San Francisco Bay National Wildlife Refuge), U.S. Geological Survey (Western Ecological Research Center, Dixon Field Station), Humboldt State University, and University of California (Santa Cruz). Colony surveys in Oregon and Washington were conducted mainly by the U.S. Fish and Wildlife Service (Oregon Coast National Wildlife Refuge and Washington Maritime National Wildlife Refuges). In British Columbia, most work from the 1960s to 1995 was sponsored and conducted by the Canadian Wildlife Service and Royal British Columbia Museum.

British Columbia, California, Oregon, Washington↗

USGS2025

Delayed incubation leads to hatching failure of a Burrowing Owl ( Athene cunicularia ) nest

Birds face strong selective pressures to complete individual nesting attempts as quickly as possible to minimize exposure of nests to predators and weather, maximize renesting potential, and maximize hatching success. As a result, the duration of developmental periods and of overall nest periods are often relatively constant within species. However, birds may sometimes be subject to acute energetic constraints that may preclude them from initiating incubation at the optimal time. We report an extraordinary case of delayed incubation by a female Burrowing Owl ( Athene cunicularia ) in Oregon, USA, which contrasted sharply with a large sample of nests monitored by motion-activated video cameras in western North America from 2015 to 2018. The focal female delayed incubation by 11 d following clutch completion and subsequently experienced near total hatching failure of her clutch. This observation corroborates previous experimental studies regarding the limits to egg viability and trade-offs between the timing of incubation onset and hatching success. These findings illustrate the acute trade-offs faced by nesting birds, and the cost of delayed incubation that we observed in this owl could help explain the cause of asynchronous hatching.

Oregon↗

USGS2019

Synopsis of research programs that can provide baseline and monitoring information for offshore energy activities in the Pacific region: Seabird and marine mammal surveys in the Pacific region

We assembled and tabulated information about marine bird and mammal research and monitoring programs that could provide data needed to support environmental risk assessments. This included identifying ongoing or completed research programs that contain information on species and habitats sensitive to offshore energy activities and that could provide baseline and monitoring data to understand and mitigate potential impacts of offshore energy development in the Southern California Planning Area, Washington-Oregon Planning Area, and the Hawaiian OCS of the Bureau of Ocean Energy Management (BOEM). When available, we also included information regarding programs in Alaska, but the catalog for Alaska is not comprehensive. We included programs that assessed the distribution, abundance, or biology of marine birds (seabirds, waterbirds, or sea ducks) and marine mammals (cetaceans, pinnipeds, and sea otters), some of which are protected species under the Endangered Species Act (ESA of 1973) or the Marine Mammal Protection Act (MMPA of 1972). We canvassed data providers with spreadsheet or web-based survey forms. The marine bird survey returned information on research and monitoring efforts for 28 parameters across 46 species from 36 entities. The marine mammal survey returned information on research and monitoring efforts for 24 parameters across 22 marine mammal species from 22 entities. We tabulated the parameters by species to show which parameters are most commonly measured and where there might be information gaps. Both marine bird and marine mammal research and monitoring are widespread throughout the Pacific, with 535 entries for marine mammals and 1,911 entries for marine birds. Although we provide summaries of key aspects within research and monitoring programs, the associated database can be further queried in several ways. Versioning of this database format essentially creates a “living database” that can be updated in the future as new information becomes available.

California, Oregon, Washington↗

USGS2019

Synopsis of research programs that can provide baseline and monitoring information for offshore energy activities in the Pacific region: Seabird and marine mammal surveys in the Pacific region

Alaska, California, Hawaii, Oregon, Washington↗

USGS2003

Status assessment and conservation plan for the Western Burrowing Owl in the United States

The Western Burrowing Owl ( Athene cunicularia hypugaea ) is a grassland specialist distributed throughout w. North America, primarily in open areas with short vegetation and bare ground in desert, grassland, and shrub-steppe environments. Burrowing Owls are dependent on the presence of fossorial mammals (primarily prairie dogs and ground squirrels), whose burrows are used for nesting and roosting. Burrowing Owls are protected by the Migratory Bird Treaty Act in the United States and Mexico. They are listed as Endangered in Canada and Threatened in Mexico. They are considered by the U.S. Fish and Wildlife Service (USFWS) to be a Bird of Conservation Concern at the national level, in three USFWS regions, and in nine Bird Conservation Regions . At the state level, Burrowing Owls are listed as Endangered in Minnesota, Threatened in Colorado, and as a Species of Concern in California, Montana, Oklahoma, Oregon, Utah, Washington, and Wyoming.

Biological Technical Publication↗

USGS2014

Sea Level Affecting Marshes Model (SLAMM) ‐ New functionality for predicting changes in distribution of submerged aquatic vegetation in response to sea level rise

Introduction Submerged aquatic vegetation (SAV) is an ecologically important habitat world‐wide. In Pacific Northwest (PNW) estuaries, SAV in the lower intertidal and shallow subtidal habitats are dominated by the native seagrass, Zostera marina Linnaeus, 1753. Within this report, SAV and seagrass refer to Z. marina seagrass beds in PNW estuaries. Z. marina provides important habitat for juvenile salmon, dungeness crabs, migratory shore birds, and benthic assemblages (e.g., Philips, 1984; Williamson, 2006; Ferraro and Cole, 2007; Shaughnessy et al., 2012). Z. marina typically occurs in a narrow depth range. For example, in Oregon estuaries Zostera marina primarily occurs within the depth range of ‐1 to +1 m relative to Mean Lower Low Water (MLLW) (Young et al. 2012). Because of their narrow depth range, the distribution of these seagrass beds are potentially vulnerable to sea level rise (SLR) through increased water depths and associated reductions in underwater light levels, alterations in tidal variations, altered water movement and wave action, and increased seawater intrusion (Short and Neckles, 1999). The “Sea‐Level Affecting Marshes Model” (SLAMM) is a moderate resolution model used to predict the effects of sea level rise on marsh habitats (Craft et al. 2009). SLAMM has been used extensively on both the west coast (e.g., Glick et al., 2007) and east coast (e.g., Geselbracht et al., 2011) of the United States to evaluate potential changes in the distribution and extent of tidal marsh habitats. However, a limitation of the current version of SLAMM, (Version 6.2) is that it lacks the ability to model distribution changes in seagrass habitat resulting from sea level rise. Because of the ecological importance of SAV habitats, U.S. EPA, USGS, and USDA partnered with Warren Pinnacle Consulting to enhance the SLAMM modeling software to include new functionality in order to predict changes in Zostera marina distribution within Pacific Northwest estuaries in response to sea level rise. Specifically, the objective was to develop a SAV model that used generally available GIS data and parameters that were predictive and that could be customized for other estuaries that have GIS layers of existing SAV distribution. This report describes the procedure used to develop the SAV model for the Yaquina Bay Estuary, Oregon, appends a statistical script based on the open source R software to generate a similar SAV model for other estuaries that have data layers of existing SAV, and describes how to incorporate the model coefficients from the site‐specific SAV model into SLAMM to predict the effects of sea level rise on Zostera marina distributions. To demonstrate the applicability of the R tools, we utilize them to develop model coefficients for Willapa Bay, Washington using site‐specific SAV data.

Oregon↗

USGS2007

Relationship of Caspian tern foraging ecology to nesting success in the Columbia River estuary, Oregon, USA

The prevalence of juvenile salmonids (Oncorhynchus spp.) and marine forage fishes in the diet of Caspian terns (Hydroprogne caspia) nesting in the Columbia River estuary has been established, but the relationship between diet composition, foraging distribution, and productivity of these birds has received little attention. We used radio-telemetry and on-colony observations to relate changes in off-colony distribution to patterns of colony attendance, diet composition, and productivity of adult terns nesting on East Sand Island during two years of different river and prey conditions. Average distance from the East Sand Island colony (located in the marine zone of the estuary) was 38% (6.6 km) greater in 2000 compared to 2001, associated with lower availability of marine forage fish near East Sand Island and lower prevalence of marine prey in tern diets. Colony attendance was much lower (37.0% vs. 62.5% of daylight hours), average trip duration was 40% longer (38.9 min), and nesting success was much lower (0.57 young fledged pair-1 vs. 1.40 young fledged pair-1) in 2000 compared to 2001. Higher proportions of juvenile salmonids in the diet were associated with relatively high use of the freshwater zone of the estuary by radio-tagged terns, which occurred prior to chick-rearing and when out-migrating salmonid smolts were relatively abundant. Lower availability of marine prey in 2000 apparently limited Caspian tern nesting success by markedly reducing colony attendance and lengthening foraging trips by nesting terns, thereby increasing chick mortality rates from predation, exposure, and starvation. ?? 2007 Elsevier Ltd. All rights reserved.

Estuarine, Coastal and Shelf Science↗

USGS2014

Recent population size, trends, and limiting factors for the double-crested Cormorant in Western North America

The status of the double-crested cormorant ( Phalacrocorax auritus ) in western North America was last evaluated during 1987–2003. In the interim, concern has grown over the potential impact of predation by double-crested cormorants on juvenile salmonids ( Oncorhynchus spp.), particularly in the Columbia Basin and along the Pacific coast where some salmonids are listed for protection under the United States Endangered Species Act. Recent re-evaluations of double-crested cormorant management at the local, flyway, and federal level warrant further examination of the current population size and trends in western North America. We collected colony size data for the western population (British Columbia, Washington, Oregon, Idaho, California, Nevada, Utah, Arizona, and the portions of Montana, Wyoming, Colorado and New Mexico west of the Continental Divide) by conducting aircraft-, boat-, or ground-based surveys and by cooperating with government agencies, universities, and non-profit organizations. In 2009, we estimated approximately 31,200 breeding pairs in the western population. We estimated that cormorant numbers in the Pacific Region (British Columbia, Washington, Oregon, and California) increased 72% from 1987–1992 to circa 2009. Based on the best available data for this period, the average annual growth rate (λ) of the number of breeding birds in the Pacific Region was 1.03, versus 1.07 for the population east of the Continental Divide during recent decades. Most of the increase in the Pacific Region can be attributed to an increase in the size of the nesting colony on East Sand Island in the Columbia River estuary, which accounts for about 39% of all breeding pairs in the western population and is the largest known breeding colony for the species (12,087 breeding pairs estimated in 2009). In contrast, numbers of breeding pairs estimated in coastal British Columbia and Washington have declined by approximately 66% during this same period. Disturbance at breeding colonies by bald eagles ( Haliaeetus leucocephalus ) and humans are likely limiting factors on the growth of the western population at present. Because of differences in biology and management, the western population of double-crested cormorants warrants consideration as a separate management unit from the population east of the Continental Divide.

Journal of Wildlife Management↗

USGS2012

Evidence for population bottlenecks and subtle genetic structure in the yellow rail

The Yellow Rail (Coturnicops noveboracencis) is among the most enigmatic and least studied North American birds. Nesting exclusively in marshes and wetlands, it breeds largely east of the Rocky Mountains in the northern United States and Canada, but there is an isolated population in southern Oregon once believed extirpated. The degree of connectivity of the Oregon population with the main population is unknown. We used mitochondrial DNA sequences (mtDNA) and six microsatellite loci to characterize the Yellow Rail's genetic structure and diversity patterns in six areas. Our mtDNA-based analyses of genetic structure identified significant population differentiation, but pairwise comparison of regions identified no clear geographic trends. In contrast, microsatellites suggested subtle genetic structure differentiating the Oregon population from those in the five regions sampled in the Yellow Rail's main breeding range. The genetic diversity of the Oregon population was also the lowest of the six regions sampled, and Oregon was one of three regions that demonstrated evidence of recent population bottlenecks. Factors that produced population reductions may include loss of wetlands to development and agricultural conversion, drought, and wildfire. At this time, we are unable to determine if the high percentage (50%) of populations having experienced bottlenecks is representative of the Yellow Rail's entire range. Further genetic data from additional breeding populations will be required for this issue to be addressed.

The Condor↗

USGS1984

Effects of heptachlor- and lindane-treated seed on Canada geese

A study of Canada geese (B. canadensis) was conducted in the Pacific Northwest from 1978 through 1981. Lowered reproductive success, mortality of adults, and a population decline of resident western Canada geese (B. c. moffitti) at the Umatilla National Wildlife Refuge (Umatilla NWR) Oregon and Washington [USA] were associated with the use of heptachlor-treated wheat. Analyses of eggs and tissues from dead geese provided strong evidence that heptachlor was responsible for the mortality and decreased production. Residues of heptachlor epoxide (HE) in brains of B. c. moffitti found dead in 1978 and 1979 equalled or exceeded the lethal hazard zone of 8-9 .mu.g/g in experimental passerine birds; HE residues of > 10 .mu.g/g in sample eggs were associated with low nest success. The breeding population of Canada geese at Umatilla decreased from 129 pairs in 1974 to about 100 pairs in 1979. The heptachlor problem was restricted to the Umatilla area; HE residues were low in tissues and eggs collected at other sites in Oregon, Washington and Idaho. In Sept., 1979, the use of heptachlor-treated seed was banned in a 1700-km2 area that encompassed both sides of the Columbia River near Umatilla. Lindane was substituted for heptachlor in the restricted area in 1979, and its use was extended to much of the Columbia Basin in 1981. Concurrently, reproductive success of geese increased, mortality decreased, and the nesting population increased to 170 pairs by 1983. There was no evidence for either biomagnification of lindance residues from treated seed to goose tissues or eggs or for induction of adverse effects by this compound.

Oregon, Washington↗

USGS2004

Site fidelity, territory fidelity, and natal philopatry in Willow Flycatchers ( Empidonax traillii )

I investigated the causes and consequences of adult breeding-site fidelity, territory fidelity, and natal philopatry in Willow Flycatchers ( Empidonax traillii ) in southeastern Oregon over a 10-year period, testing the general hypothesis that fidelity and dispersal distances are influenced by previous breeding performance. Willow Flycatchers adhered to the generally observed tendencies of passerine birds for low natal philopatry and high breedingsite fidelity. Site fidelity (return to the study area) of adult males (52.0%) and females (51.3%), and median dispersal distances between seasons (16 m vs. 19 m) were similar. Previous breeding performance and residency (age-experience), but not study-site quality, explained site fidelity in females. Site fidelity of females rearing 4–5 young (64.4%) exceeded that of unsuccessful females (40.0%), breeding dispersal was less (successful: 15 m; unsuccessful: 33 m), and novice residents were more site-faithful than former residents. Probability of site fidelity was higher for previously successful females (odds ratio = 4.76), those with greater seasonal fecundity (odds ratio = 1.58), novice residents (odds ratio = 1.41), and unparasitized females (odds ratio = 2.76). Male site fidelity was not related to residency, site quality, or previous breeding performance. Territory fidelity (return to the previous territory) in females was best explained by previous breeding performance, but not by site quality or residency. Previously successful females were more likely to return to their territory of the previous season than either unsuccessful (odds ratio = 14.35) or parasitized birds (odds ratio = 6.38). Male territory fidelity was not related to residency, site quality, or previous breeding performance. Natal philopatry was low (7.8%) and similar for males and females. Site quality appeared to influence philopatry, given that no birds reared at a low-quality study site returned there to breed, and birds reared there dispersed farther than birds reared at two other study sites. My results partially support the hypothesis that site fidelity is an adaptive response: (1) previously successful females that switched territories underperformed those that did not switch ( P = 0.01); and (2) previously unsuccessful females that switched territories outperformed those that did not switch, but not significantly ( P = 0.22).

The Auk↗

USGS2022

Postbreeding movements and molting ecology of female gadwalls and mallards

The wing molt is an important annual life-history event that occurs in waterfowl and molt site selection can play an important role in determining survival. We tracked postbreeding movements of gadwall ( Mareca strepera ) and mallard ( Anas platyrhynchos ) females that bred in the Suisun Marsh (Suisun) of California, USA, to determine molt site selection and wing molt chronology. We attached backpack transmitters with global positioning system and global system for mobile communications (GPS-GSM) technology to female gadwalls and mallards within Suisun and tracked the birds following the breeding season during 2015–2018. We determined molt locations for 52 female gadwalls and 112 female mallards. Thirty of the marked gadwall females selected 2 regions within southern Oregon-northeastern California (SONEC) to undergo molt; 16 molted in the Upper Klamath Basin (southern OR) and 14 in the Lower Klamath Basin (northeastern CA). A large portion of female mallards molted in Suisun ( n = 34) and the Sacramento Valley in California ( n = 31) but also used the Upper Klamath Basin ( n = 13), Lower Klamath Basin ( n = 12), and the Yolo–Delta region in California ( n = 12). On average, gadwalls departed Suisun on 30 July (±17.82 days [SD]), and mallards departed on 24 July (±22.69 days). Mean start date of molt for each species was similar: 27 August (±16.09 days) for gadwalls and 26 August (±21.03 days) for mallards. Molt end date was analogous for each species as well. Molt ended on average 1 October (±15.52 days) for gadwalls and on 5 October (±18.34 days) for mallards. Gadwalls and mallards showed intraspecific differences in average molt start and end date within the 3 main geographical zones: Suisun, Central Valley of California (Central Valley), and SONEC. Mean duration of wing molt for gadwalls was 34.72± 8.62 days and 41.09 ± 12.54 days for mallards. Both species primarily selected permanent marsh to undergo wing molt (gadwalls = 90.4%, mallards = 63.4%). Conservation and active management of these high-use molting areas used by California's primary breeding waterfowl species could enhance postbreeding survival, leading to increased breeding waterfowl populations.

California, Nevada, Oregon↗

USGS2007

Waterfowl distribution and abundance during spring migration in Southern Oregon and Northeastern California

We used aerial surveys to study abundance and distribution of waterfowl (ducks, geese, swans, and coots) during spring in southern Oregon and northeastern California (SONEC). Total waterfowl-use days in SONEC during the 119-day, 5 January-3 May, spring period was similar during 2002 (127,977,700) and 2003 (128,076,200) and averaged 1,075,900 birds per day (bpd); these estimates should be adjusted upward 4%-10% to account for areas not surveyed. Waterfowl abundance peaked in mid-March in both years: 2,095,700 in 2002 and 1,681,700 in 2003. Northern Pintail (Anas acuta) was the most abundant species in both years, accounting for 25.6% of the 2002 and 24.5% of the 2003 waterfowl-use days. Pintail abundance peaked during the 13 March survey at 689,300 in 2002 and 532,100 in 2003. All other dabbling ducks accounted for 27.6% and 28.6%, diving ducks for 13.5% and 9.2%, geese for 24.6% and 29.3%, swans for 2.8% and 1.0%, and coots for 5.8% and 6.4% of the spring waterfowl-use days in SONEC during 2002 and 2003, respectively. Although use days changed little for total waterfowl (+0.08%) and dabbling ducks (-0.1%), diving duck use was lower (-32%), and goose use days were greater (+19%) in 2003 than in 2002. Distribution was similar in both years, with the most waterfowl use in the Lower (66%) and Upper (14%) Klamath subregions; 2%-6% occurred in each of the other subregions. Although the Lower Klamath subregion received the greatest overall waterfowl use, distribution among subregions varied among species and surveys, and all subregions were important during some part of the spring for 1 or more species. Peak spring abundance in SONEC during 2002 and 2003 averaged 50.3% of the midwinter abundance in California (all survey regions) and southern Oregon (69-3 survey region) for all waterfowl, 46.1% for dabbling ducks, 62.4% for diving ducks, 68.8% for geese, 109.4% for swans, and 43.8% for coots. Each spring, 75% of all waterfowl use in SONEC occurred on federal, state, or Nature Conservancy lands (i.e., protected areas). On protected areas there was a higher percentage of dabbling ducks (80.5%), geese (70.5%), and coots (81.5%) than diving ducks (60.4%) and swans (49%). Waterfowl use of Klamath Basin National Wildlife Refuge (NWR) averaged 42% greater during spring 2002-2003 (568,500 bpd) than during 1998-2001 (Gilmer et al. 2004). Numerous factors likely impacted magnitude and distribution of waterfowl use of SONEC during spring, including weather, waterfowl populations, SONEC habitat, and species ecology. SONEC is a critical spring staging area for waterfowl that winter in the Central Valley of California and other Pacific Flyway regions and should be a major focus area for waterfowl-habitat conservation efforts.

Western North American Naturalist↗