Resources

Gulf of Maine Library Collection

Identification of Important Habitats in the Lower Casco Bay (Maine) Watershed

Chapter 8. Canada Goose Habitats

GENERAL: The Canada goose, Branta canadensis, is a large and abundant waterbird of the Atlantic coastal flyway, and one of the species from the Gulf of Maine Council's Species List for Identifying Regionally Significant Habitats. Although resident populations have been increasing in the Northeast, habitat use in the Casco Bay study area still is dominated by migratory birds of the Atlantic flyway. The analysis identifies aquatic (foraging and probably resting) habitats and some upland foraging areas for Canada geese, and sensitivity zones in which development may degrade adjacent habitats. These coverages are not intended to depict the limits of areas being managed or under regulatory control.

SOURCES OF BIOLOGICAL AND SPATIAL DATA: Biological data included the CWCA's (MDIF&W), eelgrass (DMR), and wetlands (NWI). We also utilized MDIF&W MHVW's for assigning habitat scores. Landcover was developed as part of this study (Chapter 3). Additional spatial information included the coastal shoreline (OGIS) and bathymetry (MGS).

HABITAT CONSIDERATIONS

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).

Resident populations (those breeding south of 47 degrees latitude) have been increasing as migratory flocks decline, leading to management concerns over damage to crops and nuisance conditions (Foss 1994). In New Hampshire and Massachusetts resident Canada goose populations readily adapt to suburban situations, nesting around artificial ponds or reservoirs and grazing on adjacent lawns. Preferred habitats include beaver ponds and ponds near pastures, preferably having small islands. Resident birds overwinter on open water near the coast. There is not a large breeding population in Maine (Sheaffer and Malecki, ms.).

In addition to the geographic shift, Canada geese now feed more commonly on uplands than occurred historically (Malecki et al. 1988). Previous to the 1960's Canada geese were known to feed 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). They eat farmland grasses/grains (leaves, roots, seeds), sedge tubers, or marsh grass seeds and roost on flooded grasslands, marshes, or open water. Migrating Canada geese are common in Maine in winter; they use ice-free fresh water and coastal marshes for resting and feeding, and agricultural land for grazing (grasses, corn stubble). Canada geese also feed heavily on eelgrass in shallow offshore waters (Thayer et al. 1984), and on marine algae (Whitlatch 1982).

MAPPING OF HABITATS

We developed a coverage of Canada goose foraging habitats in the Casco Bay study area, and sensitivity zones in which development may degrade adjacent habitats (Figure 8c). Suitable conditions included shallow waters with an abundance of plant foods, or agricultural fields suitable for gleaning or grazing. We selected the following cover types: mud flats, grain fields, salt marshes, and shallow protected waters.

In lieu of information on minimum distances between foraging sites and development we used the MDIF&W disturbance buffers for wetlands (Jones et al. 1988). These were applied as a 30 m sensitivity zone for "low value" foraging habitats, and a 90 m zone for "moderate" or "high" value foraging habitats. Upland habitats were not assigned a sensitivity zone.

The steps in mapping habitats were:

1) select polygons from the MDIF&W CWCA's hosting =>1% of the Casco Bay total Canada goose count, for any one of the seasons surveyed. The 1% criterion reduces the scope of the analysis to habitats likely to be significant from a population standpoint.

a) select areas within these polygons that are <= 1 m deep. Assign these a relative score of 4. The scores are used when combining coverages for various species.

b) select areas within the polygons from step (2) having eelgrass beds, estuarine emergent vegetation, or other aquatic vegetation. Assign these a relative score of 8.

2) select polygons from the MDIF&W CWCA's that were used by 1% or more of the Casco Bay total Canada goose count for more than one season. Select areas within these polygons that are <= 1 m deep and; score these as 8.

3) select all other estuarine/marine aquatic beds or estuarine emergent vegetation <= 1 m deep, freshwater aquatic beds and palustrine emergent; score these as 4.

4) select the agriculture class from the satellite landcover (this is based largely on signatures from corn fields) that are =>5 acres; score these 4.

5) select MDIF&W inland MHVW rated 2 or 3; where these overlay palustrine emergent or aquatic beds assign these a score of 8, otherwise score as 4.

6) select estuarine, riverine, lacustrine, palustrine open water within 90 m of wetlands of step (4) above, score as 4.

7) identify sensitivity zones for above (except agriculture fields); use a distance of 30 m for areas scored 4 and 90 m for areas scored 8. Assign habitats within the sensitivity zone distance of existing development one-half the score of pristine habitats.

To menu for file download

<RETURN TO TABLE OF CONTENTS>