Description and Ecology: On the Great Plains, shore and bank habitats historically were restricted largely to rivers (Licht 1997). Descriptions of a very wide South Platte River flood plain bordered by only a few trees and laced with sandbars are common (Knopf and Scott 1990, Kingery 1998). The flood plain geomorphology of the Arkansas River suggests that, although not as wide as the South Platte, it also was marked with numerous sandbars. This habitat is formed by two ecological processes, erosion and flooding (Busch and Scott 1995). The former continues today while the latter is highly altered. Islands, beaches, and sandbars are greatly diminished in number and extent, resulting in declines of birds that utilize these habitats (Andrews and Righter 1992). Simply put, these land forms are not being created as large or as often as historical records indicate they once were.

The current extent of beaches and shorelines is greatly diminished along rivers, but man has created a new source of these habitats--reservoirs. The excavation and water management of reservoirs creates shoreline and beach. Such beaches are now the key remaining breeding sites for two priority bird species. The persistence of these habitats depends upon water levels remaining below capacity during the breeding season and/or upon adequate windblown deposits, usually from reservoir bottoms, creating active beach and dune ecosystems.

Bank habitat results from erosion. The habitat generally occurs along stream or valley corridors, but can occur in other areas where slope is excessive relative to the soils it is supporting. Banks are also a common feature of man-made habitats, e.g., mines, highway embankments, and borrow pits. There is likely a decrease in the natural bank formations along many stream courses; however, there is also an increase in the same due to manmade features.

Although shore/bank habitats support some vegetative growth, they are most notable for their lack of vegetation. The actions of inundation, waves, and wind greatly inhibit vegetative growth. In fact, relatively small increases in plant density and height make the habitat unsuitable for most shore/bank bird species.

In addition to providing breeding habitat for a few species, the shore/bank habitat provides foraging habitat for many other species. Even in the winter, these habitats are often occupied by Horned Larks, pipits, and various sparrows.

Importance and Conservation Status: Thirteen of Colorado's breeding bird species are dependent on shore/bank habitats. This is 5% of the breeding species on less than 1% of the state's surface area. Shore/bank obligates have specialized adaptations necessary to achieve breeding success in these harsh habitats. As so often happens in nature, these specialized adaptations, combined with the small areas that the birds occupy, make shore/bank species highly susceptible to human-caused changes in the environment. Such changes are almost certain because these habitats are associated with water; in the arid West, the association of an important habitat type with water is reason for concern.

Two of the three high priority species, Piping Plover and Least Tern, no longer breed in native habitat in Colorado; all of their reproduction takes place on the shores and islands of reservoirs. The third, the Snowy Plover, has its largest populations associated with reservoirs. It is ironic that the sources that altered the native habitats to water management have also created the last nesting areas for these birds. Reservoir management has become the key to successfully conserving these birds in Colorado (Nelson 1998a,b).

Although people have created an abundance of shore and beach around reservoirs, only a few reservoir sites meet the requirements of these specialized birds. Key threats to birds in this habitat include flooding, trampling by livestock, predation, overheating of eggs and young, off-road vehicle traffic, and vegetation encroachment (Gaines and Ryan 1988; Haig et al. 1992; Nelson 1998a,b). The rarity of existing breeding sites necessitates a site-specific approach to management, and raising the numbers of sites and birds should be a key strategy.

Least Terns and Piping Plovers are critically imperiled in Colorado. Each species has fewer than 25 pairs breeding in Colorado. Where they occur on state-managed land, the sites receive intensive management. But the control of water levels is critical to success and dependent upon private water users.

Shore and bank habitat suitable for reproduction of the high priority species has always been rare, and natural occurrences of these habitats have all but disappeared. The development and maintenance of reservoirs has created surrogate patches of habitat, however, and these are now the only sites used by these species. Treating water as a property and managing it for a variety of purposes has presented significant challenges to conservation success and has resulted in urgent conservation needs for the high priority species.

Priority Species Accounts: Three species are identified as high priority in shore/bank habitats in Physiographic Area 36: Snowy Plover, Piping Plover, and Least Tern.