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TABLE 1. Reports of parasitic egg laying among No1•th American waterfowl. The area of observation and the authority follow each host. A. Species parasitized by the Redhead Coot (Fulica americana) American bittern (Botaurus lentiginosus) Pintail (Anas acuta

A two-summer, mark-recapture study of Laysan Ducks (Anus laysanensis) resulted in a population estimate of 5 10 birds with over 90% of the birds marked. Individuals seemed long-lived with the low reproductive rate common to K-selected species. Nesting occurred in spring and early summer in spite of the subtropical climatic regime. Nests were mainly in clumps of grass (Eragrostis) and hatching success was low. Duckling mortality due to exposure was common during rainstorms, but no direct predation was noted. Pair-bond behavior resembled that of continental populations of Mallards (Anus plutyrhynchos) but males tended to return to mates after brood-rearing or loss of brood or nest. Year-to-year mate switching occurred more than half the time, even when previous mates were alive. Males did not assist in care of the brood. During spring and summer, ducks of all ages fed heavily on invertebrates. Adult brine flies (Neoscutellu sexnotutu) on mud flats around the lake were the major food of ducks of all ages. Radio-marked pairs consistently used the same upland areas during the day. At night, most ducks moved to a lake on the island to feed, and to drink in communal areas at freshwater seeps. Feeding and drinking was dominantly crepuscular and nocturnal at the lake, but laying hens or hens with broods sometimes fed throughout the day as well. Conservation of the species requires monitoring of duck populations and habitat conditions, and surveillance for accidentally introduced predators such as rats. The lake is vital to the success of the species, and it is unlikely that a significant population could survive on terrestrial resources alone. Intensive management will be necessary only if blowing sands fill the lake, predators become established, or the vegetation is seriously damaged in some way.

/ Wetlands are attractive to vertebrates because of their abundant nutrient resources and habitat diversity. Because they are conspicuous, vertebrates commonly are used as indicators of changes in wetlands produced by environmental impacts. Such impacts take place at the landscape level where extensive areas are lost; at the wetland complex level where some (usually small) units of a closely spaced group of wetlands are drained or modified; or at the level of the individual wetland through modification or fragmentation that impacts its habitat value. Vertebrates utilize habitats differently according to age, sex, geographic location, and season, and habitat evaluations based on isolated observations can be biased. Current wetland evaluation systems incorporate wildlife habitat as a major feature, and the habitat evaluation procedure focuses only on habitat. Several approaches for estimating bird habitat losses are derived from population curves based on natural and experimentally induced population fluctuations. Additional research needs and experimental approaches are identified for addressing cumulative impacts on wildlife habitat values.Wetlands are attractive to many species of wildlife, often because of their great productivity, which provides nutrients and other resources used by diverse groups (Odum 1971, Tiner 1984. In addition, wetlands may be structurally diverse, providing unique habitats to which species have adapted. Certain groups of wildlife, notably birds, are among the most conspicuous of wetland animals, and because they often are tied to specific life forms of vegetation, assessment of habitat involves features such as vegetation structure that are also useful in classification of wetland types and in assessing other wetland values.Concerns over cumulative impacts of human actions on wetland habitats seem to have focused on two major types o~ perturbations: (1) cumulative losses of wetlands from multiple causes, resulting in reduced size, changes in pattern, fragmentation, reduced number, or reduced contiguity between wetlands; or (2) repeated perturbations such as contamination by single or multiple pollutants. In both cases, the effect of the impact is that the individual wetlands, wetland complexes, or wetland districts no longer function as habitat at their former levels--if at all. But there, are many other perturbations that affect wetlands in less conspicuous but significant ways, such as modification of water levels on a landscape or watershed scale, excessive grazing or repeated fires that modify detrital cycleg, increases in siltation that influence the nutrient base or turbidity and hence the nature and rate of plant succession, changes in salinity due to water , for a more complete list related to wildlife habitat issues). Moreover, many of these influences can operate at different levels; partial drainage is more serious in concert with heavy siltation, at the early seed germination and plant growth stages, when bird nesting is at its peak, or when it occurs regularly each...