dive that had been adequately documented. 



Little information is available on feeding techniques but these ducks prob- 

 ably employ a variety of methods to obtain food (Palmer 1976b). Submergence 

 times are long; Cramp et al. (1977) cited studies giving the range of time that 

 Oldsquaws remained below the surface as 30-40 sec, 30-60 sec, and 22-61 sec. 

 Birds in flocks may dive in synchrony (Palmer 1976b) or they may dive one after 

 the other in a long line (Cramp et al. 1977). Oldsquaws usually feed by day, 

 but they may also feed nocturnally (Millais 1913 iri Cramp et al. 1977). Winter- 

 ing birds move inshore to feed, then out to roost. The timing of such movements 

 varies widely with a number of environmental factors (Palmer 1976b). 



Peterson and Ellarson (1977) recently studied the food habits of the Old- 

 squaw on Lake Michigan and concluded that animal matter comprises most of the 

 diet. They also concluded that the Oldsquaw is an opportunistic feeder that 

 eats any food which is sufficiently numerous or readily available. Most of 

 this food is living animals, but Oldsquaws have also been known to dive for 

 discarded offal (Peterson and Ellarson 1977) and to feed on long-dead fish. 



Crustaceans and molluscs are often principal components of the diet. Old- 

 squaws collected on Lake Michigan from 1951 to 1954 had eaten 99% (by volume) 

 animal food. Most of it (52-96%, depending on the sample area) consisted of a 

 single amphipod ( Pontoporeia af finis ). This animal was also an important item 

 of diet in a large sample of Oldsquaws collected on Lake Michigan from 1969 to 

 1972. During the latter period this amphipod was present in 95% of all Old- 

 squaw gullets that contained any food (Peterson and Ellarson 1977). Rofritz 

 (1977) found that all the identifiable stomach contents from Oldsquaws collected 

 in the Milwaukee harbor consisted of oligochaete sludge worms ( Tubifex tubifex 

 and Limnodrilus hof fmeisteri ) . Studies cited in Palmer (1976b) and Bellrose 

 (1976) suggest a proportion of animal food ranging from 88 to 100% of the diet. 



Other animals eaten include a variety of molluscs (e.g., snails, cockles, 

 clams, chitons), crustaceans (e.g., isopods, amphipods, shrimp, crabs), various 

 insects (mostly aquatic forms), fish (e.g., gobies, cod, flatfish, minnows), 

 fish eggs (e.g., stickleback, herring), echinoderms, and annelids (e.g., earth- 

 worms, cutworms) (authors cited J^n Bellrose 1976, Palmer 1976b, Cramp et al. 

 1977, Peterson and Ellarson 1977). 



The small amount of plant material eaten includes such items as pondweeds, 

 various parts of sedges and grasses, filamentous algae, moss, berries, tubers, 

 roots, and leaves (Palmer 1976b, Cramp et al. 1977). 



We have found no reports of food habits of the Oldsquaw in southeastern 

 waters aside from an occasional anecdotal remark in the distributional litera- 

 ture. More extensive reviews of foods eaten by Oldsquaws are provided by Johns- 

 gard (1975), Bellrose (1976), Palmer (1976b), Cramp et al. (1977), and Peterson 

 and Ellarson (1977). 



SUSCEPTIBILITY TO OIL POLLUTION 



The Oldsquaw is a frequent victim of oil pollution and is known to have 



344 



