Snowy Plover Use of Coos bay North Spit, Oregon

Abstract

We studied occurrence and activities of Snowy Plovers (Charadrius alexandrinus) at Coos Bay North Spit, Oregon, from September 1981 through July 1982. We found an average of 30.0 adults at the ocean beach during winter months and an average of 20.5 adults primarily at the ocean beach and dredged-material disposal sites during the breeding season. Density of breeding adults at the southern disposal site was similar to density at the ocean beach, but significantly greater than density at the other disposal sites. Higher nest density, 0.36 nests/ha, and greater nest success, 56%, occurred at the southern disposal site. The only successful nests observed were at the southern disposal site. Adults fed more at the ocean beach than at disposal sites. We concluded that both the ocean beach and disposal sites, especially the southern site, were important Snowy Plover habitats, the beach for feeding and the disposal sites for nesting. We recommended management of these habitats for Snowy Plovers. Recent surveys along the Oregon coast have revealed only about 100 breeding adult Snowy Plovers distributed among 12 discrete beach segments (Wilson-Jacobs and Meslow 1984). Average nest success (percent nests hatching one or more eggs) at four coastal locations in Oregon during 1978 and 1979 was estimated as only 13% (Wilson-Jacobs and Meslow 1984), with a maximum of 6 of 21 chicks fledging from the 9 successful nests (Wilson 1980). These data suggest that low reproductive success is at least partially responsible for the low numbers of Snowy Plovers on the Oregon coast. However, the information on nest and fledging success was obtained from locations where abundance of breeding Snowy Plovers was low compared to their abundance at Coos Bay North Spit (hereafter, North Spit). North Spit was first recognized as an important area for Snowy Plovers in 1972, when 18% of all Snowy Plovers observed during an August survey of the Oregon coast were found there (39 of 216 plovers; W. Hoffman, unpubl. data). Only one other discrete beach segment contained more plovers (Sutton Creek, Lane County, with 47 plovers). During annual breeding season surveys of the Oregon coast conducted from 1978 to 1982, the greatest numbers of breeding adult Snowy Plovers were found at North Spit except for 1978 when dredged-material disposal sites on the spit were not surveyed (Oregon Dept. Fish and Wildl., unpubl. data; Wilson-Jacobs and Meslow 1984). Use of disposal sites at North Spit for nesting was first documented in 1979, with the observation of nests and unfledged young there (Wilson 1980). Furthermore, disposal sites seemingly provided important breeding habitat because 54% of all Snowy Plovers observed during breeding season surveys of North Spit from 1979 to 1982 were at disposal sites (Table 1). The purpose of this study was to examine use of beach and disposal site habitats at North Spit by Snowy Plovers, especially during the breeding season. Higher levels of use or greater nest success at disposal sites compared to beach habitat could explain the higher abundance of Snowy Plovers at North Spit. Specific objectives were to determine and compare for the two habitats 1) seasonal patterns of distribution and abundance, 2) numbers and densities of nests, 3) nest success, and 4) levels of feeding activity of Snowy Plovers.