cribed a behavior in which birds arose from the rear of a flock on the surface 

 of the water, pattered through or flew over the birds in front of them, and then 

 dove into the water, evidently to seize fish. The mergansers that found them- 

 selves at the rear of the flock then did likewise. An editorial note pointed 

 out that this may not have been feeding behavior but may have been a form of 

 "diving-play." 



Palmer (1976b) and Cramp et al. (1977) provided extensive summaries of 

 foods eaten by Red-breasted Mergansers, and can be consulted for detailed lists 

 of specific organisms eaten. Most of our brief summary of food habits is de- 

 rived from these two sources. 



Red-breasted Mergansers largely feed on fish; one study dealing with food 

 habits in North America indicated that about 87% of the diet was fish, the re- 

 mainder consisting primarily of crayfish and shrimp. The fish eaten are small, 

 usually less than 8-10 cm in length. Fish making up a significant part of the 

 diet in one part of range or another include Salmon ( Salmo salar ) , sculpins 

 ( Cottus asper , C . gobio ) , blueback herring ( Alosa aestivalis ) , herring ( Clupea 

 pallasii ) , sticklebacks ( Gasterosteus spp., especially G. aculeatus ) , and min- 

 nows ( Phoxinus ) . Shrimps eaten include Pandalus and Crago . Other foods taken 

 to a lesser extent include fish eggs, frogs ( Rana ) , annelids, (nereids, Lubri- 

 cidae) , insects (nymphs of dragonflies [Anisoptera] , mayflies [Ephemerida] , 

 aquatic Coleoptera [e.g., Dytiscus ] , and larval craneflies [Tipulidae] and 

 caddisflies [Trichoptera] ) , amphipods ( Gammarus ) , crabs ( Carcinus , Lophopano - 

 peus ) , prawns (Palaemonidae) , and molluscs (Hydrobira, Mytilus , Littorina , 

 Cardium , Mya) . 



Exceedingly little is known of food habits in the southeastern United 

 States. A wintering bird collected in South Carolina contained only top min- 

 nows (Gambusia) (Sprunt and Chamberlain 1949). 



IMPORTANT BIOLOGICAL PARAMETERS 



Egg Laying In North America, nests may be initiated in late May, but the 

 season more frequently begins in mid June. Nests may be started as late as mid- 

 July (Bellrose 1976). The peak of laying in Britain is in May and early June, 

 and in Iceland occurs during the first three weeks of June (authors cited ^n 

 Cramp et al. 1977 ). 



Mean Clutch Size In North America, nests hold 5-11 eggs, with an average 

 of 7.8 per nest; clutches in Europe average slightly larger (Bellrose 1976). 

 Palmer (1976b) indicated that first clutches usually contain 7-11 eggs. Re- 

 placement clutches in Finland averaged 6.2 eggs. Eggs are sometimes laid in 

 dump nests, or in nests of other birds of this or other species (Palmer 1976b). 



Incubation Period Bellrose (1976) cited a figure of 30 days for confined 

 birds in England. Palmer (1976b) cited studies of clutches in the wild, with 

 incubation periods from 29 to 35 days, usually 32 days. 



Hatching Success Little exact information is available. Many nests are 

 abandoned, and not all eggs hatch in nests that produce young (Palmer 1976b). 



429 



