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California's Central Valley wintering waterfowl: Concerns and challenges
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Tracking white-fronted geese from Bristol Bay, Alaska, to Mexico
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Hard times for nesting ducks on Grizzly Island
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Farm bill conservation programs can help meet the needs of spring-migrating waterfowl in southern Oregon-northeastern California
The Southern Oregon-Northeastern California (SONEC) region is an important migration and breeding area for Pacific Flyway waterfowl. Through a Conservation Effects Assessment Project (CEAP) partnership, the Intermountain West Joint Venture conducted a preliminary analysis of the contribution of SONEC Wetlands Reserve Program (WRP) enrollments in meeting recently established spring migrating waterfowl habitat objectives. Results suggest that WRP wetlands may meet up to 21 percent of the energetic needs for spring-migrating dabbling ducks in SONEC at North American Waterfowl Management Plan goal levels.
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.
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.
Waterfowl ecology and avian influenza in california: Do host traits inform us about viral occurrence?
We examined whether host traits influenced the occurrence of avian influenza virus (AIV) in Anatidae (ducks, geese, swans) at wintering sites in California's Central Valley. In total, 3487 individuals were sampled at Sacramento National Wildlife Refuge and Conaway Ranch Duck Club during the hunting season of 2007-08. Of the 19 Anatidae species sampled, prevalence was highest in the northern shoveler (5.09%), followed by the ring-necked duck (2.63%), American wigeon (2.57%), bufflehead (2.50%), greater white-fronted goose (2.44%), and cinnamon teal (1.72%). Among host traits, density of lamellae (filtering plates) of dabbling ducks was significantly associated with AIV prevalence and the number of subtypes shed by the host, suggesting that feeding methods may influence exposure to viral particles. ?? 2010 American Association of Avian Pathologists.
Feeding ecology of waterfowl wintering on evaporation ponds in California
We examined the feeding ecology of Northern Pintails (Anas acuta), Northern Shovelers (A. clypeata), and Ruddy Ducks (Oxyura jamaicensis) wintering on drainwater evaporation ponds in California from 1982 through 1984. Pintails primarily consumed midges (Chironomidae) (39.3%) and widegeongrass (Ruppia maritima) nutlets (34.6%). Shovelers and Ruddy Ducks consumed 92.5% and 90.1% animal matter, respectively. Water boatmen (Corixidae) (51.6%), rotifers (Rotatoria) (20.4%), and copepods (Copepoda) (15.2%) were the most important Shoveler foods, and midges (49.7%) and water boatmen (36.0%) were the most important foods of Ruddy Ducks. All three species were opportunistic foragers, shifting their diets seasonally to the most abundant foods given their behavioral and morphological attributes.
Increased body mass of ducks wintering in California's Central Valley
Waterfowl managers lack the information needed to fully evaluate the biological effects of their habitat conservation programs. We studied body condition of dabbling ducks shot by hunters at public hunting areas throughout the Central Valley of California during 2006–2008 compared with condition of ducks from 1979 to 1993. These time periods coincide with habitat increases due to Central Valley Joint Venture conservation programs and changing agricultural practices; we modeled to ascertain whether body condition differed among waterfowl during these periods. Three dataset comparisons indicate that dabbling duck body mass was greater in 2006–2008 than earlier years and the increase was greater in the Sacramento Valley and Suisun Marsh than in the San Joaquin Valley, differed among species (mallard [ Anas platyrhynchos ], northern pintail [ Anas acuta ], America wigeon [ Anas americana ], green-winged teal [ Anas crecca ], and northern shoveler [ Anas clypeata ]), and was greater in ducks harvested late in the season. Change in body mass also varied by age–sex cohort and month for all 5 species and by September–January rainfall for all except green-winged teal. The random effect of year nested in period, and sometimes interacting with other factors, improved models in many cases. Results indicate that improved habitat conditions in the Central Valley have resulted in increased winter body mass of dabbling ducks, especially those that feed primarily on seeds, and this increase was greater in regions where area of post-harvest flooding of rice and other crops, and wetland area, has increased. Conservation programs that continue to promote post-harvest flooding and other agricultural practices that benefit wintering waterfowl and continue to restore and conserve wetlands would likely help maintain body condition of wintering dabbling ducks in the Central Valley of California.
An agent-based model to quantify energetics, movement and habitat selection of mid-continent mallards in the Mississippi Alluvial Valley
The dynamics of wintering waterfowl populations at the landscape scale are the result of complex interactions of environmental, behavioral and energetic drivers. Agent-based models provide a method to directly link these factors in a spatially explicit framework and allow the emergence of patterns from the aggregation of individual agent actions. We adapted the Spatially-explicit Waterbird Agent-based Model Program (SWAMP), originally developed for waterfowl in central California, to simulate a basin-scale population of mallards ( A. platyrhynchos ) wintering in the Mississippi Alluvial Valley over a four-month period (November–February). Simulated agents move within the landscape, foraging on areas made available based on a probabilistic inundation status, and converting food resources to endogenous energy. The model uses a high-resolution map of eastern Arkansas waterfowl habitats and incorporates a hierarchical habitat selection system that enables mallards to relocate at increasing scales in response to changing food availability. We validated the performance of modeled mallard body condition and behavioral metrics under a range of environmental conditions against expected outcomes derived from empirical data and found that the simulation produced realistic representations of changes in flight distances, energy expenditure, lipid storage, and foraging habitat use in response to depleting food resources over time. We discuss the model's applicability as a tool to quantify waterfowl response to a range of environmental conditions and to evaluate scenarios of landscape composition and configuration in the context of waterfowl population management.
Duck harvest on public hunting areas in California
We summarized hunter visits and success, and the magnitude and species composition of the duck harvest recorded on California public hunting areas (PHAs) during 1950-87. Hunter visits and harvest increased during 1950-74 as new PHAs were added, then declined concurrently with duck populations. Of six geographic regions, the Sacramento Valley, with numerous PHAs and the largest duck concentrations, accounted for the largest portion of PHA hunter visits (28%) and harvest (35%). Duck population levels, regulations, and hunter numbers affected PHA hunter success. Success was highest during 1955-59 but declined with no consistent trend after 1960. Species vulnerability, abundance, distribution, and hunter preference affected harvest composition. Northern pintails, Anas acuta, averaged 27% of the PHA harvest but declined in importance after 1974. Green-winged teal, A. crecca, the most important species in southern regions, averaged 21% of the PHA harvest. Mallards, A. platyrhynchos, averaged 16% of the PHA harvest but increased in importance after 1974 to become the most common duck bagged after 1983. PHA harvest comprised a small (4-16%) portion of the total state harvest. However, this portion increased from 1950-70 because of increased hunter visits to new PHAs and after 1970 because hunter success on PHAs did not decline as on other areas. PHA hunters tended to harvest fewer preferred species and more vulnerable species, as proportions of total bag, than did other hunters. The continued decline in numbers of waterfowl hunters presents important challenges for management of waterfowl areas in California.
Kidney lesions associated with mortality in chickens inoculated with waterfowl influenza viruses
Seventy-six type A influenza viruses recovered from waterfowl in Wisconsin, California, South Dakota, Florida, Texas, Alabama, and Nebraska were tested for virulence in chickens. The challenge to chickens was intravenous inoculation of first-, second-, or third-egg-passage virus. Each of the virus strains was tested separately in three or four chickens. Eighteen of the 76 viruses caused the death of one or more chickens following inoculation. Postmortem lesions were similar in all dead birds. In decreasing order of frequency, gross lesions included: swollen kidneys evident as accentuated lobular patterns, urates in the pericardial sac, and urates on the surface of the liver. Microscopic lesions present in kidneys were consistent with visceral gout. Mortality was associated with inoculations having higher concentrations of infectious virus. These results indicate that the influenza A viruses circulating in duck populations may include strains potentially pathogenic for chickens.
Rice available to waterfowl in harvested fields in the Sacramento Valley, California
Rice fields in the Sacramento Valley, California were sampled in 1985 and 1986 to determine the weight of rice seed remaining in the fields immediately after harvest and again after the fields were burned. No significant differences were found between years (P>0.05). The pooled mean was 388 kg/ha in harvested fields and 276 kg/ha in burned fields. These values are less than estimates previously available. The values for harvested fields both years were no different (P>0.05) than values obtained by the U.S. Department of Agriculture (USDA). Surveys of rice fields in December both years showed that most fields were left either harvested (26-32%) or burned (37-40%) through the winter. Fields flooded for duck hunting made up 15% of the total. The proportion of fields plowed by December increased from 14% in 1985 to 22% in 1986. Sixty-three percent of all fields that had been flooded for hunting were drained within two weeks after the end of the hunting season. Harvest yield field size levee type (contour, lasered), straw status (spread, windrowed), harvest date, and rice variety did not affect the quantity of seeds remaining after harvest (P>0.05). One harvester model, the Hardy Harvester, left more rice in fields than did others we tested (P<0.001). Specific management programs are recommended to mitigate annual variation in rice seed availability to waterfowl caused by differences in total hectares grown (15% less in 1986) and in the proportion of fields burned and plowed.
Rice available to waterfowl in harvested fields in the Sacramento Valley, California
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Effects of irrigation on seed production and vegetative characteristics of four moist-soil plants on impounded wetlands in California
We examined the effects of irrigation on 4 moist-soil plants commonly managed for waterfowl in the Sacramento Valley, California. Irrigation resulted in taller and heavier swamp timothy ( Heleochloa schoenoides ), pricklegrass ( Crypsis niliaca ), and sprangletop ( Leptochloa fasicularis ). Barnyardgrass ( Echinochloa crusgalli ) grew taller in irrigated wetlands, but no significant difference in weight was detected. Only sprangletop yielded larger seed masses in response to irrigation. Without irrigation, swamp timothy and pricklegrass assumed a typical prostrate growth form, but with irrigation, they assumed a vertical growth form. Irrigation did not significantly affect plant density. Because of rising water costs, wetland managers should consider wildlife management objectives and plant responses before implementing irrigation practices.