1994-1997 Lake Powell Winter Aquatic Bird Surveys, Glen Canyon National Recreation Area, Utah and Arizona

Spence, John

This report presents the results of a three-year survey of aquatic birds on Lake Powell, Glen Canyon National Recreation Area. Aquatic birds were defined as members of all families from Gaviidae through Anatidae and all families from Rallidae through Laridae (1998 AOU sequence). Surveys were conducted monthly between September and April from 1994 through 1997. Each survey was three days long, and covered standardized routes in seven deSignated survey areas on the 150-mile long reservoir. Over the course of the study 72,893 individuals of 54 species were detected. This represents 70% of all aquatic species documented on Lake Powell. The most common species were, in order of abundance, American Coot, Western Grebe, Gadwall, Green-winged Teal, Ring-billed Gull, Common Goldeneye, and Redhead. The first two accounted for 80% of all detections, and the seven most common species accounted for 89% of all detections. Diving species were most abundant, accounting for 90% of all detections. Several rare or new species were documented for Glen Canyon NRA and Lake Powell, including Yellowbilled Loon, Red-necked Grebe, Greater Scaup, Surf Scoter, White-winged Scoter, Barrow's Goldeneye, Oldsquaw, and Herring Gull. Numbers of birds generally peaked in November, although significant numbers were also found on December and January surveys. Species richness and diversity were greatest in spring. The most commonly utilized habitats on Lake Powell were shallow-water bays «100 foot depth) and shorelines with drowned tamarisk scrub. Principal components analysis indicated that species assemblages were fairly consistent over fall migration and winter, but were much more unpredictable during spring migration. Changes in assemblages also reflected differences in reservoir water levels and the abundance of small fish. At higher water levels birds were generally more common, and a Significant positive relationship was found in some survey areas between Western Grebe abundance and Threadfin Shad abundance. Survey data from January 1988 indicate that few if any Significant changes appear to have taken place in over-wintering assemblages in the last 9 years. Comparisons with other reservoirs along the Colorado River are made, as are recommendations for future surveys.

1994-1997 Lake Powell Winter Aquatic Bird Surveys, Glen Canyon National Recreation Area, Utah and Arizona

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