Temporal Pattern of Wetland Use by Eurasian and American Wigeon in the Northern Sacramento Valley, California

The Eurasian Wigeon (Anas penelope; hereafter EUWI), a close relative of the American Wigeon (Anas americana; hereafter AMWI) and Chiloé Wigeon (Anas silbatrix) of North and South America, breeds throughout Northern Eurasia and winters in portions of western Europe, Africa, and India (Johnsgard 1978; Madge and Burn 1988). The nearest known EUWI breeding habitats to North America occur within the Anadyr River basin in the Russian Far East near the Bering Sea (Vaurie 1965; Lehman 2005). The use of North American wetlands by wintering EUWI has been well documented (Hasbrouck 1944; Bellrose 1980), with most winter records coming from the Pacific and Atlantic Flyways; however, EUWI are more common throughout the Pacific Flyway (Dunn and Alderfer 2011). As most records of EUWI from the Aleutian (for example, Shemya Island; Gibson 1981) and Bering Sea islands, Alaska (for example, St. Lawrence Island; Lehman 2005) are documented during fall and spring, it seems likely that most if not all migratory movements between Asia and the Pacific Flyway are made using these insular corridors (Winker and others 2007). Christmas Bird Count data for the Pacific Flyway show an upward trend in EUWI numbers beginning in the 1960s and continuing today (National Audubon Society 2009), although reasons for this trend are unclear (Edgell 1984). Waterfowl Harvest and Parts-Survey data for the Pacific Flyway and Alaska show a similar upward trend for the period of 2005–2008 (USFWS 2014a), with the highest EUWI harvest recorded in 2006 (1712 birds) and 2007 (2232 birds). Although the ecology of EUWI has been studied extensively in the Old World (Lebret 1950; Donker 1959; Owen and Williams 1976; Rijnsdorp 1986; Jonsson and Gardarsson 2001), there have been no such studies in North America. As California wetlands provide winter habitat for between 4 and 5 million waterfowl, including 70 to 80% of Pacific Flyway wigeon (for example, 76% in 2008; USFWS 2014b), our study goal was to gain a better understanding of the migration chronology and temporal pattern of wetland use by EUWI in the Sacramento Valley, California. Additionally, as there appears to be a very close association between EUWI and AMWI on our study units, we collected comparative data for AMWI as an initial attempt to better understand the sympatric interactions of these 2 species throughout the fall and winter months. Migratory waterfowl, including EUWI, have been implicated as potential long-distance vectors for avian influenza viruses such as highly pathogenic (HPAI) Subtype H5N1 (Winker and others 2007; Keawcharoen and others 2008; Kim and others 2009; Pearce and others 2009). However, whether HPAI H5N1 is actually maintained in wild duck populations is currently unresolved (Krauss and others, 2007; Kim and others 2009; Takekawa and others 2010). In laboratory studies, ducks that illustrate immunity to HPAI H5N1 are known to shed the virus from their respiratory and digestive tracts (Kim and others 2009). Keawcharoen and others (2008) found the rate of HPAI H5N1 excretion by experimentally infected EUWI to be low relative to several Palearctic pochards (Aythyini) and Mallards (Anas platyrhynchos); of the 6 duck species used in their study, EUWI were considered among the least likely to serve as a longdistance vector for this virus. Nevertheless, their results showed that although EUWI manifest no clinical signs of the disease, they are susceptible to this virus. Also, Keawcharoen and others (2008) isolated HPAI H5N1 virus from 4 of 8 EUWI pharyngeal samples, and they detected productive viral infections in 7 of GENERAL NOTES