Feeding strategies and habitat use in four wading bird species

Double Crested Cormorant "are opportunistic, generalist feeders" (Wires, Cuthbert, Dale, & Joshi, 2001). They feed on slow moving fish species that range from 3 centimeters to 40 centimeters. These birds forage in shallow water and seem to be strict diurnal in the way they eat. They are quick to respond to areas with high fish concentration and flock where the fish can easily be caught.

The Double Crested Cormorant breeds in cold climatic conditions and has been living in Alaska for a long time (Wires, Cuthbert, Dale, & Joshi, 2001, p. 36). According to Siegel-Causey & Savinetskii (1991), the remains of the bird have been found on Amchitka Island dating back over 2000 years. These remains suggest that the there were plenty of the species in the central Aleutian Islands and climate changes have reduced their population in Alaska.

Great Blue Herons

Great Blue Herons are prey generalists, although they forage for fish. They catch their prey as they walk along the shores of water bodies such as oceans, lakes, marshes and even rivers. On the mainland, the bird preys on small animals such as rodents (Butler, 1992). The mainland foraging is done in the winter when the shores are frozen and fish is unavailable, or when the young ones are learning hunting skills (Butler, 1991). The Great Blue Herons also prey on amphibians, reptiles, invertebrates and birds. They catch their prey by a quick head and neck thrusts.

Great Blue Herons breed in various regions of the world, but in North America, the Ardea Herodias occidentalis are found in the warmer regions such as Florida. "The Herodias fannini are non-migratory found in the Pacific coast from Washington States to Alaska and Herodias found between south Canada to Galapagos" (Butler, 1992). The size of the colony on all these species depend on foraging area.

American Robin

The American Robins are generalist and feeds on invertebrates, such as beetles, caterpillars, grasshoppers, fruits and barriers (Dewey & Middleton, 2002). These birds forage on the ground for soft bodied invertebrates. They find their prey by sight not by sound, "pounce on them and pull them up" (Cornell Laboratory of Ornithology, 2007). Robins of the coastal regions feed on insects and mollusks found on the shores (Clement, Hathway, & Wilczur, 2000).

The American Robin is found throughout North America. It moves to northern parts of the United States over winter or south of Canada from Florida. According to BirdLife International (2004), the robin's range is quite extensive and estimated at over 15 million square kilometers with a large population of 320 million birds.