Our Llvliii^ Hi'Sdiira's — Bir(l.\ 



37 



During the driest periods, however, such as 

 those in the 1980"s. only the deepest and most 

 permanent wetlands retain water, causing popu- 

 hition declines in species such as pintails that 

 rely primarily on shallow wetlands. Population 

 numbers are more stable for species like the 

 canvasback. which rely on deeper marshes, and 

 are therefore less affected by annual changes in 

 wetland numbers because deeper marshes con- 

 sistently retain water, providing ample habitat 

 in most years (Stewart and Kantrud 1973). 



Nest success in the Prairie Pothole region 

 has declined in recent years largely because of 

 increased nest predation caused by the range 

 expansion of some predators and by reduced 

 nesting habitat (Sargeant and Raveling 1992). 

 Fewer and smaller areas of nesting habitat con- 

 centrate duck nests, enhancing the ability of 

 predators to find nests. Predators such as rac- 

 coons (Procyon lotor) have expanded their 

 range northward, probably because they can 

 den in buildings, rock piles, and other human- 

 made sites during winter. 



Although wetland drainage, urbanization, 

 and other human-caused changes have resulted 

 in wintering habitat losses, these losses have 

 been offset, at least for dabbling ducks, by 

 increased fall and winter food from waste grain 

 left in stubble fields. In addition, the national 

 wildlife refuge system has protected and man- 

 aged many staging and wintering areas for the 

 benefit of waterfowl. 



Modern duck-hunting regulations are 

 believed to keep recreational harvest at levels 

 compatible with the long-term welfare of duck 

 populations. The proportion of ducks harvested 

 varies regionally and by species, age. and sex. 

 In 1992. 2^-12% of the adult mallards from the 

 Prairie Pothole region were killed by hunters. 

 Harvest rates of other species were generally 

 lower. These conservative harvest rates are 

 unlikely to cause population declines (Blohm 

 1989). 



Conclusions 



Changes in duck populations reflect changes 

 in quality and quantity of waterfowl habitats. 

 Long-term declines in populations have been 

 caused by extensive habitat alterations. By con- 

 trast, short-term changes primarily reflect 

 weather and resultant availability of wetland 

 habitats. Maintenance of the cuirent monitoring 

 system and initiatives to improve our monitor- 

 ing capability are essential for effective duck 



management. 



Maintaining or increasing the quality and 

 quantity of waterfowl habitat is needed to stabi- 

 lize or increase duck populations. Agricultural 

 policies and practices can profoundly affect 

 habitat availability in Canada and the United 

 .States. For example, the Conservation Reserve 

 Prograiu. in which certain agricultural areas 

 were set aside and planted in grasses, has added 

 much-needed dabbling duck nesting habitat and 

 therefore has improved their productivity in the 

 U.S. portion of the Prairie Pothole region (R.E. 

 Reynolds. USFWS. personal communication). 

 The North American Waterfowl Management 

 Plan, through its regional joint ventures, is striv- 

 ing to increase the habitat available for water- 

 fowl and to improve monitoring of some popu- 

 lations. 



References 



Belliose. F.C. 1980. Duck.s. geese and swans of North 

 America. }n} ed. Stackpole Books. Harrisbiirg. PA, 540 



PP 

 Blohm. R.J. 1989. Introduction to harvest: understanding 



surveys and season setting. Pages 118-129 //; K.H. 



Seattle, ed. Sixth International Watertbvvl Symposium. 



Washington. DC. 

 Caithamer. D.F. J. A. Dubovsky. F.A. Johnson. J.R. Kelley. 



Jr.. and G.W. Smith. 1993. Waterfowl; status and fall 



night forecast. Administrative Rep.. U.S. Fish and 



Wildlife Service. Washington. DC. M pp. 

 Conroy M.J., J.R. Goldsberry. J.E. Hines. and D.B. Stotts. 



1988. Evaluation of aerial transect surveys for wintering 



American black ducks. Journal of Wildlife Management 



52:694-70-3. 

 Eggeman. D.R.. and FA. Johnson. 1989. Variation m effort 



and methodology for the midwinter waterfowl inventory 



in the Atlantic" Fly way. Wildlife Society Bull. 17:227- 



233. 

 Hochbaum. G.S.. and E.F. Bossenmaier. 1972. Response of 



pintail to improved breeding habitat in southern 



Manitoba. Canadian Field-Naturalist 86:79-81. 

 Johnson. D.H.. and J.W. Grier 1988. Detenninants of 



breeding distributions of ducks. Wildlife Monograph 



100:1-37. 

 Kaminski. R.M., and M.W. Weller. 1992. Breeding habitats 



of nearctic waterfowl. Pages 568-589 in B.J. Batt. A.D. 



Afton. M.G. Anderson. CD. Ankney. D.H. Johnson. J. A. 



Kadlec, and G.L. Krapu, eds. Ecology and management 



of breeding waterfowl. University of Minnesota Press. 



Minneapolis. 

 Sargeant. A.B.. and D.G. Raveling. 1992. Mortality during 



the breeding season. Pages 396-422 in B.J. Batt. A.D. 



Afton. M.G. Anderson. CD. Ankney. D.H. Johnson. J. A. 



Kadlec, and G.L. Krapu. eds. Ecology and management 



of breeding waterfowl. University of Minnesota Press, 



Minneapolis. 

 Smith. R.I. 1970. Response of pintail breeding populations 



to drought. Journal of Wildlife Management 34:943-946. 

 Stewai-t. R.E., and H.A. Kantrud. 1973. Ecological distribu- 

 tion of breeding waterfowl populations in North Dakota. 



Journal of Wildlife Management 37:39-50. 



For further information: 



David F Caithamer 



U.S. Fish and Wildlife Service 



Office of Migratory Bird 



Management 



Henshaw Laboratory 



11500 American Holly Dr. 



Laurel. MD 20708 



