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.