Wildlife & Habitat


If you were teaching a class in ecology, Cold Springs National Wildlife Refuge would be the perfect example of "juxtaposition" and "edge effect." (To find out what these are, read on.)



A mix of several distinct habitat types—open water, riparian, shrub-steppe upland and seasonal wetlands—attracts a variety of wildlife to the refuge. The open water habitat of the reservoir provides isolation for the resting needs of migrating waterfowl. Large numbers of waterfowl, primarily Canada geese and mallards, can be seen on the open water in winter. They move between the reservoir and the river daily, looking for food or quiet space.

Dense, wide stands of cottonwoods and willows represent the riparian zones on the Cold Springs National Wildlife Refuge. The area where water meets the land is especially important because it offers wildlife many food and shelter choices. The thick underbrush provides excellent habitat for many species of songbirds. It is also a good place to look for deer, elk and other animals feeding or resting.

The shrub-steppe upland consists of sagebrush, bitterbrush, rabbitbrush and native bunchgrasses. Mule deer, coyotes, badger, ring-necked pheasant, California quail and the small resident elk herd can be seen using the uplands throughout the year. Look for Swainson's, Coopers and red-tailed hawks and American kestrels soaring over the uplands.

The shrub-steppe, representative of plant communities once very common in this part of the country, is threatened by invasive exotic plants, such as cheatgrass, false indigo and Russian olive. The native plants cannot compete for water and nutrients as well as these exotics, which thrive in stressed or disturbed conditions. Wildlife, having been sustained for ages by native plants, start to decline because exotic plants do not typically provide the needed food nor shelter.


Birds flying along the Pacific Flyway, the migration route linking Alaska, Canada, the western states, Mexico and South America, use the Cold Springs National Wildlife Refuge as a stopover during their journeys. Thousands of songbirds find food and shelter here during the winter months. Large numbers of waterfowl can be seen as they spend a part of their day resting on the refuge. Bald eagles can be seen during these months, watching the waterfowl, waiting for a possible meal.

As winter fades to spring, most of the waterfowl and songbirds depart for northern nesting grounds. Some mallards, teal, wood ducks and many songbirds stay to nest and raise their families. When water levels recede in the summer months, look for shorebirds such as least sandpipers, killdeer, western sandpipers, long-billed dowitchers and American avocets probing the exposed mudflats for food. Colonial nesting birds, like great blue herons and double-crested cormorants, can also be seen then.

Although migration times provide spectacular wildlife scenes, animal can be seen using the refuge year-round. California and ring-billed gulls are year-round residents, as are California quail and ring-necked pheasants. Look for signs of beaver in riparian areas. Deer can be seen browsing or resting in both the riparian and upland areas. Also look for upland birds, such as the long-billed curlew and burrowing owl.

Okay, long enough. What are juxtaposition and edge effect? Turn the page . . .


In ecology, juxtaposition refers to the amount of interspersion of different habitat types. It's related to the edge effect described below in that the more juxtaposition, or interspersion, of habitat, the more edge is created.


Edge Effect

In ecology, edge effect refers to the changes in the population or community structure that occurs at the point where two habitat types meet. Edge effects are especially pronounced in small habitat fragments (i.e., more juxtaposition of habitats), where the edge effects may extend throughout the patch. Increasing edge effects allows more habitat structure, which generally increases biodiversity within the area.

Differing environmental conditions enable certain species of plants and animals to colonize on the borders of habitats. Plants that colonize these areas tend to be shade-intolerant and tolerable of dry conditions, such as shrubs and vines. Animals that colonize tend to be those that require two or more habitats, such as mule deer, elk and bluebirds. Some animals may travel between habitats, while those that are restricted only to the edge are known as edge species. Larger patches include more individuals and therefore have increased biodiversity.

These areas offer unique habitats with easy access to adjacent communities and therefore can support more plants and animals from these adjacent communities. These species can adapt and increase the area's biodiversity. The easy flow of animals to adjacent areas creates travel lanes along borders.

There is an increased availability of light to plants along the borders that promotes primary production. For example, the increased availability of light can allow more plants to be supported, which increases herbivorous insects and then nesting birds, and nest predators are attracted.

However, while many species benefit from juxtaposition and edge effect, and biodiversity is generally higher, many other species suffer. For example, some species require large areas of similar habitat to survive, such as wolverines and spotted owls.