Inflatable Dam Proposal Comments
R. L. Wasilewski, Vice President, Greater Wyoming Valley Audubon Society
Potential Impacts of an Inflatable Dam
If an inflatable dam is installed in the Susquehanna River in Wilkes-Barre, the impoundment created, and the increased active recreation that the impoundment may support, are likely to have negative impacts on the wildlife within the River corridor. Inundation of islands and shorelines would at least severely limit the amount of, and possibly eliminate, foraging areas for wading birds such as great egrets, great blue herons, and black-crowned night herons. Since many of these areas are also used by waterfowl, breeding ducks would suffer from a lack of slowly-moving water in which young ducklings can safely forage. Furthermore, since the resident peregrine falcons may prey on waterfowl (A common name of the peregrine is "duck hawk."), reductions in waterfowl numbers could affect the peregrines' food supply. Although the falcons have successfully preyed upon rock doves in the downtown Wilkes-Barre area, it may be a mistake to assume, without sufficient data regarding prey items taken by the peregrines, that the falcons can survive and successfully raise young by relying solely on the availability of urban prey species. Moreover, while the islands and shorelines help to support resident and migrant species of wading birds and waterfowl, thereby supporting potential prey for the peregrines, I have observed the peregrine falcons using these areas as well. One particular cobble bar near the North Cross Valley Expressway bridge is exposed during low-water episodes, and is used by the peregrines for bathing and loafing. Recently when the COE was presented with the option of excavating this cobble bar for incorporation as stabilization material in the levee, COE officials chose to avoid disturbing the cobble bar based upon the peregrines having been documented as using it. (J. Griff, pers. comm.).
In addition to inundating valuable island and shoreline habitats, the impoundment created by the inflatable dam would submerge snags that are used for perching by double-crested cormorants. The pool may also threaten riparian forests via submersion of root systems by infiltrating ground water, as suggested by Smith and others (1995). Damage to these forest areas would reduce or eliminate nesting habitat for a variety of songbirds and raptors, and would degrade or eliminate valuable stopover habitat for migrating songbirds. This latter type of habitat is receiving increasing attention for its value to migrants, most notably to immature songbirds, which may congregate in such areas during their first autumn migrations (Yong and others 1998). The 1998 North American Fall Migration Count documented a number of such species in the River corridor (Personal observation), including cedar waxwing (Bombycilla cedrorum), blue-headed (solitary) vireo (Vireo solitarius), Nashville warbler (Vermivora ruficapilla), northern parula warbler (Parula americana), yellow warbler (Dendroica petechia), chestnut-sided warbler (D. pensylvanica), magnolia warbler (D. magnolia), Cape May warbler (D. tigrina), yellow-rumped warbler (D. coronata), black-throated green warbler (D. virens), bay-breasted warbler (D. castanea), American redstart (Setophaga ruticilla), scarlet tanager (Piranga olivacea), rose-breasted grosbeak (Pheucticus ludovicianus), and indigo bunting (Passerina cyanea). Hence, loss of, or damage to, the Susquehanna's riparian forests could have severe consequences for the River corridor's avian diversity.
While the pool created by an inflatable dam would have its own negative consequences for the area's avifauna, the increased recreation that may result could have additional adverse impacts. Jahn and Hunt (1964) have noted that "activities of shoreline residents, fishermen, and boaters discourage breeders [waterfowl] from using otherwise adequate habitat" on Wisconsin lakes, and they cite similar evidence from Mendall (1958), who suggested that brood survival among ring-necked ducks (Aythya collaris) in Maine increased when fishing and boating were prohibited. Jahn and Hunt (1964) further suggested that the American black duck (Anas rubripes), which is found in the Susquehanna River in the Wilkes-Barre area, is among the species that are least tolerant of human disturbance. This could represent a significant management concern given the apparent decline of this species locally as evidenced by National Audubon Society Christmas Bird Count data (E. Johnson, pers. comm.), especially if the species is experiencing similar declines in other parts of its range.
Further evidence of adverse impacts to breeding waterfowl was offered by Reichholf (1976), who reported that within a single decade, the presence of anglers during the breeding season led to a 90% decrease in breeding stocks of waterfowl on several oxbows near the River Inn on the Bavarian-Austrian border. Robertson and Flood (1980) observed that human activities caused eastern kingbirds (Tyrannus tyrannus) and common loons (Gavia immer) to leave their nests during incubation, thereby possibly resulting in chilling of eggs or nestlings, and in increased vulnerability to predators. Although loons are not known to nest within the Susquehanna River corridor in the Wyoming Valley, other species of waterfowl are likely to exhibit similar reactions to human disturbance, with similarly detrimental consequences. Such adverse impacts of human disturbance were documented for double-crested cormorants by Ellison and Cleary (1978), who found that "adults were less protective of eggs and young and readily left their nests when [the researchers] approached." Cormorants have yet to be documented as breeding in the Wyoming Valley. However, the presence of adult cormorants throughout the summer months, and the presence of both adults and young cormorants during late summer, suggest that such documentation may be forthcoming. The cormorant's status as a breeding bird in the Wilkes-Barre area notwithstanding, a dramatic increase in active recreation within the River corridor, as has been suggested would occur in response to impounding the River behind an inflatable dam, may exceed the levels to which local populations of avian species have become tolerant. The repercussions that have been documented for the above-noted species therefore could be expected to be the same for those species that currently breed, or that may soon begin to breed, within the River corridor in Wilkes-Barre.
Uncontrolled active recreation could also adversely affect waterfowl during post-breeding periods. Reichholf (1976) argued that undisturbed areas are "essential for survival" of molting waterfowl, and he described the molting season as "one of the most critical periods in the annual life cycles of ducks." The impoundment created by an inflatable dam could jeopardize molting waterfowl on the Susquehanna River by providing access to otherwise relatively inaccessible islands and shoreline areas, which are the types of areas in which molting ducks would normally find refuge from predators during this flightless period of their life cycles. Finally, Korschgen and others (1985) determined that boating disturbed migrating waterfowl on the upper Mississippi River from September through November. Since the inflatable dam would maintain a recreational pool during part of this time period, similar disturbances of migrating waterfowl could be expected on the Susquehanna River.
Negative impacts of increased recreation also could be felt by breeding and migrating wading birds, and by migrating raptors. Reichholf (1976) reported that human recreation caused black-crowned night herons to fail to breed on their traditional nesting grounds in an Austrian bay. In studies of the breeding success of black-crowned night herons that were intentionally subjected to disturbances by researchers, Tremblay and Ellison (1979) found that such disturbances "reduced nesting success by inhibiting laying, by increasing either nest abandonment or egg predation, and by increasing nestling mortality...." Parsons and Burger (1982) found that black-crowned night heron nestlings defecated and/or regurgitated in response to human disturbance. While this behavior may have "predator avoidance value," the researchers noted that such behavior "could also result in significant loss of food if disturbance is frequent" (Parsons and Burger 1982). Knight (1984) found that wintering bald eagles were intolerant of "high activity" levels, and that human activity caused eagles to be "displaced to marginal habitat...." Although bald eagles would not be affected if they were present in the impoundment area during the winter months when the dam would be deflated, the increasing number of bald eagles, and the presence of an immature eagle in the impoundment area during the 1998 breeding season, suggest that non-breeding and post-breeding eagles may find suitable foraging and resting habitat along the Susquehanna River in the Wyoming Valley. Thus, care should be taken to protect areas of suitable habitat, such as the riparian forests and large islands, and the relatively large expanses of undisturbed open water, from excessive traffic and human disturbance. Furthermore, since ospreys, another large raptor that is intimately associated with large bodies of water, and that is currently listed as endangered in Pennsylvania, use the Susquehanna River in the impoundment area during post-breeding dispersal and migration, limiting active human use of the River would benefit this species. Although the osprey has been proposed for downlisting to threatened (Brauning 1998), the species would still require special management consideration in areas in which it occurs.