of mussels and clams, has caused considerable public concern in Maine. A very 

 limited collection of eiders (<20 birds) feeding in an area where mussels were 

 highly toxic, revealed the birds had been feeding largely on nontoxic crabs 

 and eider tissues contained very low concentrations of the toxin (personal 

 communication from G. G. Donovan, Maine Department of Inland Fisheries and 

 Wildlife, Augusta, ME.; August, 1977). The relation of the red tide organisms 

 to waterfowl needs further investigation. 



The mergansers, with the possible exception of the hooded merganser, are 

 primarily fish eaters. Although not abundant breeders in coastal Maine, the 

 common merganser may be a troublesome predator on juvenile salmonids in rivers 

 and ponds (Munro and Clemens 1937; and Elson 1962). 



A winter food relationship among eels, common mergansers, and bald eagles has 

 been established in the rivers and estuaries of coastal Maine. According to 

 studies by R. B. Owens, Jr. (personal communication, School of Forest 

 Resource, University of Maine, Orono , ME.; February, 1979), the mergansers 

 feed heavily on small eels, some of which might be heavily contaminated with 

 heavy metals or pesticides. The contaminated mergansers are fed on by bald 

 eagles which assimilate the contaminants in their body tissues. It is not 

 known how serious this problem is in Maine (although heavy metal and pesticide 

 residues are high in nonproductive eagle eggs), or how the contaminants affect 

 mortality rates of wildlife or threaten human health. 



Another interaction that has management implications is the competition for 

 nest boxes. Erected for nesting wood ducks, goldeneys, and hooded mergansers, 

 MDIFW studies (Spencer and Corr 1977) indicate as many as 10% of these 

 occupied boxes may contain mixed clutches with two of the three species. In 

 addition, American kestrels, tree swallows, starlings, bees, and hornets 

 frequently use nest boxes, reducing the value of the boxes for tree-nesting 

 ducks. Carefully selected sites, proven installation techniques, and regular 

 maintenance greatly enhance their use by nesting ducks. 



FACTORS AFFECTING DISTRIBUTION AND ABUNDANCE 



The many factors affecting the distribution and abundance of a species or 

 group of species at various times and places are difficult to measure. 

 Natural and human-made factors known to influence coastal waterfowl are 

 described below. 



Natural Factors 



Natural factors influencing population size and distribution are disease, 

 parasites, predation, quantity and quality of habitat, food supplies, and 

 weather. The only disease troublesome to coastal Maine, primarily in the 

 Penobscot Bay area, is fowl cholera ( Pasteurella multocida ) which afflicts 

 nesting eider ducks (Gershman et al. 1964). Since its discovery in 1963 near 

 Camden, it has reoccurred in several years but has not been widespread. Fowl 

 cholera can cause the loss of nearly all adult females in a specific island 

 nesting colony, but islands only a few miles away may escape the disease 

 entirely. The disease does not appear to measurably reduce the breeding 

 population coastwide. Annual monitoring of the disease's occurrence and 

 sanitation operations, when necessary, is a continuing need. 



15-35 



10-80 



