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.
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).
Due to extremely low numbers of EUWI relative to AMWI, we employed different survey techniques for monitoring each species through time.
EUWI were censused through complete searches of each unit.
We quantified numbers of each wigeon species biweekly, and by management unit, as the average number of wigeon per transect (AMWI) or per unit census (EUWI).
We tested for differences in the temporal pattern of wetland use between species and by management unit using Kolmogorov-Smirnov one-sample goodness-of-fit tests, with the null hypothesis being that the biweekly pattern of wetland use for AMWI and EUWI are the same for each management unit.
Initial use of T13.3 by AMWI was documented during the 29 August-12 September 2007 biweekly period, whereas our earliest record for EUWI occurred during the 12-25 October 2006 period (Appendix).
Initial use of T12 by AMWI and EUWI occurred immediately following flood-up in early November (Appendix).
Although no comparative EUWI data exist for the Pacific Flyway, our EUWI arrival dates in early October are consistent with fall records of migrating EUWI on both the Aleutian and Bering Sea (for example, St.
We therefore suggest that differences in the temporal pattern of wetland use by AMWI and EUWI that we found in our study are likely due to one or more of these environmental factors.