The California Current Marine Bird Conservation Plan (original) (raw)

The coastal and offshore areas of the California Current region provide a variety of feeding, roosting, and nesting habitat for seabirds. The abundant food in the California Current, resulting from high ocean primary productivity, attracts millions of seabirds that breed and/or migrate throughout this region annually, with the non-breeders outnumbering the breeders year-round (1, 2). Marine habitat characteristics and "quality" vary spatially and temporally, within and between seasons, years, and decades. Naturally occurring climate cycles in the world's oceans and atmosphere operate at several scales and strongly influence the CCS and, therefore, the ocean habitats that seabirds depend on for their survival, including habitat-specific productivity and predator-prey relationships. While the mechanisms of climate change are not well understood, it seems clear that climate cycles and change in ocean habitats, prey availability, and prey quality are critically linked to changes in seabird demography. In this section we summarize both terrestrial and marine habitat used by seabirds for breeding, roosting, and feeding in the CCS region. Oceanographic and atmospheric processes leading to marine climate variability on multiple temporal scales, and the response of seabirds to this variability, are discussed in detail in Chapter 5. 3.1 TERRESTRIAL HABITAT (A1). General Habitat Description The coastal and offshore areas of the West Coast provide a variety of roosting and nesting habitat, including islands, rocks, cliffs, headlands, beaches, estuaries, and even humanmade structures such as bridges, dikes, dredge spoil islands, jetties, and breakwaters. Islands, however, are disproportionately important sites for roosting and nesting. There are numerous islands off the west coast of North America, several of which contain seabird colonies exceeding 100,000 breeding birds. Numerous bays and estuaries along the mainland coast also provide critical habitat for many seabird species. The largest of these are Puget Sound in northern Washington, the Columbia River estuary on the border between Oregon and Washington, and San Francisco Bay in California. These protected coastal areas provide important breeding habitat, especially for coastal terns and gulls. East Sand Island in the Columbia River estuary supports the largest Caspian Tern colony in the world and the largest Doublecrested Cormorant colony in the Pacific. a. Islands-Islands, by their very nature, are isolated and typically provide seabirds with a protected habitat where they can breed and roost with little danger and few disturbances. The largest seabird colonies and the vast majority of breeding seabirds are found on islands, especially on those that are small to medium-sized. Islands are quite variable and have defining features that affect the species and number of seabirds that utilize them, such as size, shape, height, geological composition, micro-habitat characteristics, distance from shore, distance to feeding areas, presence or absence of soil, extent and depth of soil, plant communities, animal communities, and history of bird use. The smaller islets and rocks often support larger numbers of seabirds. Smaller islands are often uninhabited and free of mammalian predators such as rats, cats, dogs, foxes, and coyotes, although this is not always the case. Included in the island category, but unique, are the low islands found in bays and estuaries. These islands form naturally when sediments fall out of suspension in the slower moving waters of the estuary. They are much more dynamic in shape, size, and composition than the rocky, marine islands and in a natural system islands appear, disappear, and continually change shape. Scoured by 1. Only the eastern 24% of Santa Cruz Island is included in the National Park, the western 76% is owned and managed by The Nature Conservancy