Waterbird and raptor use of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California, 1984-1986

Graduation Date

1989

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Wildlife Management, 1989

Committee Chair Name

Stanley Harris

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Birds of prey, Marsh ecology, Humboldt County, Water birds, Humboldt State University -- Theses -- Wildlife Management, California, Arcata Marsh and Wildlife Sanctuary

Abstract

Waterbird use and aquatic vegetation structure of the Arcata Marsh and Wildlife Sanctuary, Humboldt County, California was studied from 9 May 1984 to 21 August 1986. Diurnal waterbird use of each marsh unit was determined by direct counts of all birds on each unit. An average of 2.4 surveys was conducted at high and also at low tide each week. Percent cover of the marsh units was determined by preparing cover maps from low altitude aerial photographs and standing crop biomass was calculated by harvesting samples from random plots. In Gearheart Marsh the coverage of common cattail alpha latifolia) nearly doubled between April 1985 and September 1987 while marsh pennywort (Hydrocotyle ranunculoides) nearly tripled. In September 198 sago pondweed (Potamogeton pectinatus) covered 77.2 percent of Gearheart Marsh. The peak sago pondweed standing crop present in Gearheart Marsh was measured in June 1985 (187.94 grams per square meter ± 113.08 g) and in June 1986 (132.77 grams per square meter ± 88.73 g). Sago pondweed was not present in Hauser Marsh in 1985 because the unit was dry during the growing season but in September 1986, there were 93.03 (± 47.66) grams per square meter. One hundred and seventy four species of birds were observed at the Marsh Project during this study. Of these, 98 species were observed on the water areas and are treated in this report. The total waterbird use-days in 1984-85 was 1,434,633 and 1,429,873 in 1985-86. Shorebirds represented 87.9 percent of all bird use-days and waterfowl, coots and rails accounted for 8.8 percent. Peak waterbird use occurred during winter, early and late spring in both years with 63.1 and 61.0 percent of the annual total bird use-days represented in those three seasons in 1984-85 and 1985-86 respectively. The lowest waterbird use occurred in summer with 0.48 and 0.42 percent of the total annual bird use-days in 1984-85 and 1985-86 respectively. Most waterbird species using the Marsh Project either had no significant difference in use rates between tide levels or were found in significantly greater numbers at high tide (p0.05). Klopp Lake had the highest percent of the total bird use-days per five hectares in both years because of large and small shorebird use. Gearheart Marsh was second and Hauser Marsh was third in percent of total bird use-days per five hectares in both years because of puddle ducks, coots and diving ducks in Gearheart and coots and small shorebirds in Hauser Marsh. Four bird groups were found in significantly different (p0.05) numbers between years on a marsh-wide basis. The fish-eating diver group occurred in significantly lower numbers in 1985-86 compared to 1984-85 mostly because of reduced numbers of double-crested cormorants and "other" fish-eating divers in Klopp Lake. Puddle ducks doubled in numbers on a marsh-wide basis because of a 72 percent increase in Gearheart Marsh principally, by green-winged teal (Ana' crecca) and mallards (A. platyrhynchos). Large shorebirds significantly decreased (p0.05) between 1984-85 and 1985-86 mostly because of a reduction of marbled godwits (Limosa fedoa) and willets (Catoptrophorus semipalmatus) in Klopp Lake. Gulls and terns significantly decreased (p0.05) marsh wide between 1984-85 and 1985-86, mainly because of a reduction of more than 50 percent in gull and tern use-days at Klopp Lake.

https://scholarworks.calstate.edu/concern/theses/n296x142x

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