Scaup Habitat Model
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Draft Date:
June 2001

Scaup; greater (Aythya marila), and lesser (Aythya affinis)

Use of Study Area Resources:
Wintering and migration. Greater scaup breed in Alaska and Canada (Terres 1980). Lesser scaup breed north of the U.S., and also in the mid-West. Both use coastal, riverine, and lacustrine open water and wetlands during migration. Lesser scaup are more prone to winter south of the Gulf of Maine and, more commonly, inland (Cottam 1939, Palmer 1975, Bellrose 1980).  Data from hunter surveys show about 60% of the scaup taken between Maine and Massachusetts are greater scaup (Bellrose 1980).

Habitat Requirements:
In migration lesser scaup seem to prefer smaller lakes, ponds, and coastal marshes (Cottam 1939, Bellrose 1980, Terres 1980), resting on flats, mudbars, ice, and other areas with little or no emergent vegetation (Mulholland 1985). Greater scaup frequent larger lakes (Palmer 1975), using both fresh and saltwater bodies depending on availability, time of year, and tide stage (Burger 1983). Wintering scaup often are found in mixed flocks on large saltwater bays, harbors, sounds and estuaries (Terres 1980, Mulholland 1985).

In coastal New England both scaup feed primarily on molluscs, commonly blue mussels, dwarf surf clams, and oysters (Cottam 1939, Cronan 1957, Bellrose 1980, Terres 1980). Those in tidal freshwater areas also ingest plant material (Cronan 1957, Bellrose 1980). Scaup have the capability to feed in water 6 to 7 m deep, but seem to prefer a depth of 1-3 m (Cottam 1939, Cronan 1957, Palmer 1975, Bellrose 1980, Terres 1980, Mulholland 1985).

Human activity in the forms of boating, hunting, and fishing may disturb scaup (Cronan 1957). Also, ice formation in bays and harbors redistribute scaup away from otherwise preferred areas (Bent 1923, Palmer 1949, Burger 1983).

Habitat mapping. We modeled inland and coastal marsh migratory habitat, and coastal wintering resources for both lesser and greater scaup.

Migration. Lakes and ponds over 1 ha in area, and regularly flooded coastal marshes both were scored as indicated in the first table (below). Portions of these within 180 m of development were given a score of 0.  The relatively low score (0.3 out of possible 1.0) reflects the lack information on specific use.

NWI Designations
(wetlands only)
Cover Types Cover Suitability
(0 - 1 scale)
Upland deciduous forest
Upland coniferous forest
Upland mixed forest
Upland shrub, regenerating forest
Bare ground
PEM_L2EM Lake/pond, emergent vegetation
PFOcon Palustrine forest, conifer
PFOdec Palustrine forest, deciduous
PSSdec Palustrine scrub shrub, deciduous
PSScon Palustrine scrub shrub, conifer
PAB_L2AB Lake/pond, aquatic vegetation
L1UB_PUB Lake/pond, unconsolidated bottom

0.3*, **

L2US Lake, unconsolidated shore
L2RS Lake, rocky shore
R1UB Riverine subtidal unconsolidated
Rper Riverine perennial
E1AB Estuarine subtidal vegetated
E1UB Estuarine subtidal unconsolidated bottom
E2AB Estuarine intertidal algae
E2EM Estuarine intertidal emergent 0.3*
E2RS_R1RS Estuarine, tidal river rocky shore
E2SS Estuarine intertidal shrub
E2US Estuarine intertidal unconsolidated shore
M1AB Marine subtidal vegetated
M1UB Marine subtidal unconsolidated bottom
M2AB Marine intertidal algae
M2RS Marine intertidal rocky shore
M2US Marine intertidal unconsolidated shore
NOTES * if at least 180 m from developed landcover
** if lake or pond 1ha or larger

Wintering.  Winter foraging habitat was identified as those estuarine and marine areas having both suitable depths (+1 to - 25 feet mean low water) and food resources for scaup (shellfish).

Beds of a variety of bivalve molluscs were identified using previously developed data for coastal New Hampshire (Banner and Hayes 1996), a Maine DMR shellfish coverage, and the NOAA 1995 National Shellfish Register coverage, characterizing shellfish growing areas by state. The latter described shellfish abundance within relatively large coastal segments, and so the information was of lower resolution and given less weight than the other sources.

The data from annual USFWS mid-winter waterfowl surveys were processed by taking the maximum counts per segment polygon (or sub-segment, where available), and calculating the number of birds per unit area. Maine's Coastal Wildlife Concentration Areas (Maine Department of Inland Fisheries and Wildlife) counts were similarly converted to birds per unit area. Potential foraging habitat (having suitable depth and shellfish) was scored 0.5 for higher resolution and 0.3 for lower resolution shellfish data. Where these potential foraging habitats coincided with the occurrence of one or more scaup per 10 ha, they were scored 1.0 and 0.6, respectively. Where water depth was suitable and scaup were present the area was scored 0.5 (see table, below).

COASTAL HABITAT SUITABILITY SCORING forage not documented apparent foraging habitat potential foraging habitat
scaup abundant 0.5 1.0 0.6
scaup uncommon 0 0.5 0.3

The migration and wintering maps then were combined, retaining the highest value per grid cell from the two maps.

Model Testing: The scaup occurrences from the Winter Waterfowl Surveys for 1999 and 2000 in Maine were used to test the wintering habitat map. We created a bounding polygon encompassing all waterfowl observations for those surveys, and created a randomly distributed set of 70 points within it. We then compared the presence of habitat near the random points to that for sites at which scaup were observed. Of the 19 sites with scaup, 17 had mapped habitat, while only 18 out of the 70 randomly distributed sites had habitat. The Chi-square was highly significant, indicating that the overall model does indicate localities useful to scaup.

Banner, A. and G. Hayes. 1996. Important Habitats of Coastal New Hampshire. USFWS Gulf of Maine Program, Falmouth, ME. 75 p.

Bent, A.C. 1923. Life Histories of North American Wildfowl. U.S. National Museum Bulletin 126. Smithsonian Institute, Washington, DC.

Bellrose, F.C. 1980. Ducks, geese and swans of North America. Wildlife Management Institute. 540 pp.

Burger, J. 1983. Jamaica Bay Studies IV. Factors affecting distribution of Greater Scaup Aythya marila in a coastal estuary in New York, USA. Ornis Scandinavica 14:309-316.

Cottam, C. 1939. Food habits of North American diving ducks. USDA Tech. Bull. 643.

Cronan, J.M. 1957. Food and feeding habits of the scaups in Connecticut waters. Auk 74(4):459-468.

Mulholland, R. 1985. Habitat suitability index model: lesser scaup (wintering). U.S. Fish Wildl. Serv. Biol. Rep. 82(10.91). 15 pp.

Palmer, R. 1949. Maine Birds. Bull. Compar. Zool. 102:99-101.

Palmer, R. 1975. Handbook of North American Birds. Yale University Press, New Haven, CT.

Terres, J.K. 1980. The Audubon Society Encyclopedia of North American Birds. Wings Books, Avenel, NJ.