Parasites may, at times, cause some waterfowl losses, but their overall effect 

 is difficult to assess. The acanthocephalan, Polymorphus botulis, is common 

 in the intestines of many Maine eiders and has caused local mortality 

 (Grenquist 1970). Blood parasites in freshwater breeding areas are commonly 

 transmitted to ducks by biting flies (Diptera). These include protozoan 

 malaria-like parasites of the genera Leucocytozoon , Haemoproteus , and 

 Plasmodium. O'Meara (1954) found an abundance of blood parasites in samples 

 of central Maine waterfowl. Infections of Haemoproteus nettionis and 

 Leucocytozoon simondi were found in more than 80% of a sample of Maine wood 

 ducks collected on the Penobscot River between Old Town and Lincoln (Thul 

 1977); <1% were infected with Plasmodium circumf lexum . Although these 

 parasites are common among waterfowl, no evidence has been found that it 

 leads to mortality. The debilitating effects of parasites probably reduce the 

 resilience of waterfowl to disease or predation. 



Predation is another natural mortality factor whose effects are difficult to 

 measure. Predation alone is not known to materially reduce waterfowl 

 populations in coastal Maine. The most serious predation affects nests, 

 nesting adults, and/or young. Mammals that prey on eggs and ducks are 

 raccoon, skunk, red fox, mink, weasels, bobcat, and perhaps coyotes. 

 Significant avian predators are gulls, crows, and great-horned owls. Owls 

 usually take adult and young ducks, whereas crows and gulls are essentially 

 nest predators. Both the herring gull and the great black-backed gull 

 regularly take ducklings. In some instances gull predation on a nesting 

 colony of eider ducks may reduce breeding success and potential. The raccoon 

 is the most serious predator on nest boxes. The snapping turtle is sometimes 

 a significant predator on young ducks in freshwater habitats. 



The distribution, size, and quality of aquatic habitats have a great influence 

 on the abundance of coastal waterfowl. Waterfowl habitat was discussed 

 earlier and is mentioned here only to recall some of the factors that may 

 influence breeding or wintering populations. 



Cavity-nesting waterfowl have the most specific nesting habitat requirements. 

 Accordiing to Spencer and Corr (1977), wood ducks, hooded mergansers, and 

 goldeneyes utilize a high proportion of artificial nest boxes in the central 

 coastal area (regions 2 and 4, particularly). Populations of these species 

 appear to have increased by well designed nest box programs. Whether this 

 reflects a lack of adequate natural sites, a preference for boxes, or greater 

 success in boxes, is unknown. It is probably safe to assume the artificial 

 boxes are less subject to predation than natural sites. 



The status of beaver populations also has a direct effect on the amount and 

 quality of waterfowl breeding habitat. In fact, beaver impoundments may be 

 the optimum habitat for black ducks, wood ducks, and hooded mergansers. 

 Depending upon the nature of the individual flowage, blue-winged teal, green- 

 winged teal, and ring-necked ducks also often utilize beaver ponds for nesting 

 and brood rearing. Optimum beaver management is also good waterfowl 

 management in Maine. 



Tidal habitat for wintering and migrating birds is highly diverse and variable 

 throughout coastal Maine. Winter-inventory data (MDIFW files) indicate 

 drastic declines in the number of waterfowl (particularly black ducks) 

 utilizing major tidal areas. Winter populations in the Kennebec River and the 



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