small animals: aquatic insects, shrimps, snails, etc. (total 70%-90%), to a much 

 lesser extent on seeds and other portions of aquatic plants." The primary foods 

 taken on fresh water in spring and summer are insects; in autumn, insects, gas- 

 tropods, and plants; and in winter, molluscs, the latter mostly snails. Birds 

 on salt water from fall through spring feed chiefly on crustaceans and molluscs 

 and to a limited extent on insects (Palmer 1976b). Erskine (1972) summarized 

 the food habits of Buffleheads by stating that in all seasons they feed primar- 

 ily on arthropods and only secondarily on molluscs; they feed chiefly on insects 

 while on fresh water and on crustaceans on salt water. The most important food 

 in marine situations are decapods, including both shrimp and crabs; isopods are 

 also frequently eaten. Minor items of diet include marine worms, bryozoans, 

 water mites ( Hydrachnida ) , and small fishes (mostly sculpins [Cottidae] ) (Erskine 

 1972). Erskine' s summary should be consulted for further details of the food 

 habits of the Bufflehead. 



Although little is known of the food habits of Buffleheads in southeastern 

 waters, presumably the foods eaten there are similar to those consumed elsewhere. 

 Quay and Critcher (1965) gave the sole report of stomach contents taken entire- 

 ly within southeastern waters. They reported that five Buffleheads wintering on 

 Currituck Sound, North Carolina, had eaten 54.6% (by volume) plant material. 

 The most important foods were pondweeds ( Potamogeton spp. - 28.6%) and widgeon- 

 grass ( Ruppia maritima - 12.6%); southern naiad ( Na jas guadalupensis - 2.0%) 

 was considerably less important. Quay and Critcher did not indicate what kind 

 of animals were eaten. 



IMPORTANT BIOLOGICAL PARAMETERS 



Egg Laying Egg-laying begins in late April in the southern parts of the 

 range but occurs later farther north. The most northern populations begin lay- 

 ing about mid-May. The period of peak laying ranges from early May to mid-May 

 from southern to northern parts of the range. Almost all laying is completed 

 by mid-June throughout the range (Bellrose 1976). 



Mean Clutch Size In studies summarized by Erskine (1972) of 263 nests, 

 the mean clutch size was 8.75 eggs; 9 eggs is the most common size. Mean 

 clutch size was smallest (7.00, n = 5 ) in southern localities (California, Ore- 

 gon), and largest (9.00, n = 18) in northern localities (Alaska). 



Incubation Period Incubation periods ranged from 28 to 33 days in British 

 Columbia (Erskine 1972). 



Hatching Success In Erskine' s (1972) study in British Columbia, some eggs 

 hatched in 75-80% of all nests; in these successful nests, about 90% of the 

 eggs laid were hatched. The average production from successful nests was 8 

 chicks, which represented a loss of less than one egg per nest. 



Fledging Success "Probably only about one-half of hatched young survive 

 to flight" (Erskine 1972). 



Age at Fledging Young Buffleheads are capable of flight at 50-55 days in 

 British Columbia (Erskine 1972). 



412 



