Livestock grazing in intermountain depessional wetlands : effects on breeding waterfowl / R.B. Harrison, W.M. Jones, D. Clark, B.A. Heise, and L.H. Fraser.

Includes bibliographical references (pages 482-484).

Livestock grazing is a prevalent land use
in western North American intermountain wetlands,
and physical and biotic changes related to grazingrelated
disturbance can potentially limit wetland
habitat value for waterfowl. We evaluated breeding
waterfowl use in 34 wetlands in relation to water
retention, amount of wetlands on the landscape, and
livestock grazing intensity. The study was conducted
over 2 years in the southern intermountain region of
British Columbia, Canada. For a subset of 17
wetlands, we measured aquatic invertebrate abundance
over 1 year. Waterfowl breeding pairs and
broods were classified into three functional groups:
dabbling ducks, and two types of diving ducks,
overwater and cavity nesters. We evaluated candidate
models with variables considered singly and in
combination using the Akaike Information Criterion.
When selected, bare ground (an indicator of grazing
intensity) and wetland density were negatively associated
with breeding use while wetland fullness and
invertebrate density were positively associated. Each
factor was a significant predictor in at least one of the
models, but unexpectedly, grazing intensity was the
most consistent predictor of waterfowl wetland use
(e.g., it was present in more ‘best models’ than
wetland fullness). Grazing was associated with declines
in the number of waterfowl pairs and broods, likely
mediated through effects on wetland vegetation and
aquatic macroinvertebrates. Models with site- and
landscape-scale variables generally performed better
than simpler models. Waterfowl breeding use of
wetlands can be improved by reduced livestock
grazing intensity adjacent to wetlands and by grazing
later in the season. Wetland water retention is also an
important constraint on waterfowl use of wetlands and
may become more limiting with a shifting climate.