. The Canadian field-naturalist. 2000 Wright, Bruner, Li, Jarvis, and Dowlan: Harlequin Ducks 191 Table 1. Spring and summer census of Harlequin Ducks on Quartzville Creek, Oregon, 1994—1997. Surveys were conducted along 15 km of stream; observations included 4 km sur- veys and mist-netting attempts. Totals included all pairs, individuals, and ducklings. Year Spring Surveys Pairs Total Summer Surveys Broods Total Summer Observations Broods 1994 9 35 1995 12 32 1996 7 19 1997 6 15 20 6 25 7 11 2 51 8. 0 20 40 60 80 Percent of Bedrock per Site Figure 2. Relationship between the number of Harlequ
. The Canadian field-naturalist. 2000 Wright, Bruner, Li, Jarvis, and Dowlan: Harlequin Ducks 191 Table 1. Spring and summer census of Harlequin Ducks on Quartzville Creek, Oregon, 1994—1997. Surveys were conducted along 15 km of stream; observations included 4 km sur- veys and mist-netting attempts. Totals included all pairs, individuals, and ducklings. Year Spring Surveys Pairs Total Summer Surveys Broods Total Summer Observations Broods 1994 9 35 1995 12 32 1996 7 19 1997 6 15 20 6 25 7 11 2 51 8. 0 20 40 60 80 Percent of Bedrock per Site Figure 2. Relationship between the number of Harlequin Duck observations and the percent of bedrock at each site in 1995 and 1996 in Quartzville Creek, Oregon. nificantly different between 1995 and 1996 (Table 4). Though densities of total benthic invertebrates in May and June 1996 were substantially lower than in 1995, abundances reached comparable levels by July (Figure 5). Total annual densities of EPT taxa were significantly lower in 1996 than in 1995 (Table 4). Harlequin Ducks and Macroinvertebrates Numbers of duck observations, within each study site, were compared to mean densities of D. gilvipes, total benthic invertebrate taxa and EPT (Ephe- meroptera, Plecoptera, and Trichoptera) taxa (see Wright 1997). These inter-site comparisons revealed no significant relationships between annual numbers of harlequins and either annual estimated means of D. gilvipes, total benthic invertebrates, or EPT taxa densities (p = , and , r2 =, and respectively) at each site. However, both ducks and caddisflies frequented areas with high proportions of bedrock (Figure 2, Table 3) Temporal overlaps between harlequins and D. gilvipes were established by qualitatively comparing harlequin arrival at Quartzville Creek, presence of males, and brood development to D. gilvipes instar maturation. Ducks arrived, paired, and copulated throughout May when D. gilvipes were developing from second to third instars (Figures 1
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