ResourcesIdentification of Important Habitats in Coastal New HampshireChapter 13. Canada GooseThe Canada goose, Branta canadensis, is a large and abundant
waterbird of the Atlantic coastal flyway. Although resident populations
have been increasing in the Northeast, migratory birds still are important
to hunters. The Atlantic coast migratory population of the Canada goose
breeds from Labrador and Newfoundland to Quebec. It now winters largely
in the mid-Atlantic states and the Carolinas; those migrating further
south have been reduced to 10% of the pre-1960's levels (Malecki et al.
1988). Changes in agricultural practices (larger fields, more corn fields),
milder winters, and creation of new wildlife refuges have encouraged the
altered migration patterns. The extreme form of this "shortstopping" behavior
is the development of resident (non-migratory) populations. In Canada's
St. Lawrence valley, goose numbers and length of stay during spring and
fall "staging" also has increased with the introduction of corn culture
and heavy spring flooding (Reed et al. 1977). In addition to the geographic shift, the birds now feed more commonly
on uplands than occurred historically (Malecki et al. 1988). Canada geese
classically fed on moist soil and aquatic plants; this now is supplemented
with corn and other upland grains, and pasture plants (Harvey et al. 1988).
Geese feed in marshes and fields up to 13 km from water, foraging first
in fields adjacent to water (Reed et al. 1977). There they eat farmland
grasses/grains (leaves, roots, seeds), sedge tubers, or marsh grass seeds
and roost on flooded grasslands, marshes, or open water. Canada geese
feed heavily on eelgrass (Zostera marina) in shallow offshore
waters (Thayer et al. 1984), and on marine algae (Whitlatch 1982). DATA SOURCES Since migratory Canada geese do not nest within the study area, we developed
simple habitat models to map just migration and wintering habitats. Habitat
maps were constructed by operating these models with digital base maps
including: bathymetry, NWI wetland types, eelgrass distribution, and landcover
(active agriculture). MIGRATION HABITAT Mapping of migration habitats was based on availability and types of
foraging areas during these seasons. Water depths > 2 feet prevent
access to food resources; deep marine and estuarine wetlands were assigned
a suitability of 0. We had no data from which to assign various scores
for the quality of migration habitat. Therefore, all wetland types potentially
used by foraging Canada geese during migration were given a "neutral"
value of 5 (0 - 10 scale) (Figure of Migration Habitat).
This included eelgrass beds and other coastal and interior wetland types
(Table 5) within the suitable depth range, and agricultural fields >=
5 acres. Table 5. Wetland Suitability as Canada Goose Migration Habitat.
WINTERING HABITAT During winter, ice and snow limit availability of freshwater wetlands
as foraging habitat, and Canada geese concentrate in Great Bay and Little
Bay, and in agricultural fields within 1 km of these tidal waters (pers.
comm. Ed Robinson, NHF&G). Although eelgrass beds are unavailable
to foraging Canada geese when ice develops on Great Bay, these beds are
of vital importance when clear. Therefore, eelgrass beds were given a
suitability score of 10 and active agricultural fields within 1 km of
Great Bay and Little Bay a score of 5 (Figure of Winter
Habitat). The migration and wintering habitat coverages were combined
using the maximum score for either function (Figure
of Combined Seasonal Habitat). |
