Oitr Uviiiii Resouixcs — Birds 



.?.5 



Mexico at regular intervals. Results from these 

 surveys are the basis for this article. 



The Breeding Population and Habitat 

 Survey is conducted during May and June when 

 most species occupy their breeding ranges. 

 Pilot-biologists and observers in airplanes iden- 

 tify and count ducks on a sample of transects. 

 Not all ducks are visible from the air. so some 

 transects are resurveyed more thoroughly with a 

 helicopter or from the ground to obtain com- 

 plete counts. These data are used to correct the 

 air counts and obtain unbiased estimates of 

 duck densities in these areas. Estimates of num- 

 ber of pairs of ducks are expanded to provide 

 population estimates for the entire surveyed 

 area. This survey, conducted by the Canadian 

 Wildlife Service and the U.S. Fish and Wildlife 

 Service (USFWS), is among the most extensive 

 and comprehensive surveys conducted annually 

 for any group of animals anywhere in the world. 

 Survey estimates are the major determinant 

 governing the regulation-setting process for the 

 sport harvesting of ducks by both Canadian and 

 United States provincial, state, and federal gov- 

 ernments. 



The Breeding Population and Habitat 

 Survey is most reliable for mallards (Anas 

 platyrhynchos), gadwall {A. strepera). 

 American wigeon (A. americaua). green- 

 winged teal (A. cvecca). blue-winged teal (A. 

 discors). northern shoveler {A. clypeata). red- 

 head (Aythya americana). canvasback (A. val- 

 isiiieria), and scaup {A. affinis and A. marila). 

 Researchers and managers are trying to expand 

 the geographic range of this survey in the 

 Pacific Flyway. eastern Canada, and the north- 

 western United States. 



The breeding survey, however, poorly moni- 

 tors species such as whistling ducks 

 (Deiidrocygihi spp. ). mottled ducks {Anas fid- 

 vigida). American black ducks (A. ruhhpes). 

 most sea ducks and mergansers (Lophodytes 

 ciicuUaliis. Mergiis merganser. M. serrator). 

 and wood ducks (Aix sponsa). 



The Midwinter Survey has been conducted 

 annually in early January since the mid-1940"s. 

 It is not as reHable as the breeding survey 

 because of methodological shortcomings and 

 because winter is a poor time to survey popula- 

 tion abundance (Eggeman and Johnson 1989). 

 Despite its limitations, this survey does provide 

 useful information on such species as the black 

 duck that are not well surveyed by the breeding 

 survey (Conroy et al. 1988). 



Status and Trends 



Population estimates of all ducks from the 

 breeding survey have varied from 26.5 to 42.8 

 million since 1955 (Fig. 2). Generally, breeding 

 populations were high in the I950's and 70"s 



and low in the 60"s, 80"s, and 90"s. The 1993 

 estimate of 28.0 million was 20% below the 

 195.5-92 average. 



Estimates of ducks from the Midwinter 

 Survey also have varied since 1955 (Fig. 2). The 

 1993 estimate of 10.3 million ducks was the 

 lowest recorded, and 44% below the 1955-92 

 average. 



The Breeding Population and Habitat 

 Survey provides reliable estimates for seven 

 species of dabbling ducks, while the Midwinter 

 Survey provides estimates for eight. The breed- 

 ing population of total dabbling ducks in 1993 

 was 20% below the 1955-92 average. 

 Compared with the 1955-92 average, 1993 

 breeding population estimates suggest popula- 

 tion declines for mallards. American wigeon. 

 blue-winged teal, and northern pintail. 

 Population estimates were unchanged for 

 green-winged teal and increased for gadwall 

 and northern shoveler (Figs. 3-5). During the 

 most recent 10-year period, the breeding popu- 

 lation of northern pintail decreased, gadwall 

 populations increased, and populations of six 

 other species were stable (Table). Midwinter 

 estimates of all species of dabbling ducks were 

 stable or increased during 1984-93 (Table). 



Midwinter estimates are the only long-term 

 data available for black ducks. Apparent differ- 

 ences in population trends between the breeding 

 and midwinter surveys (Table) are a function of 

 differences in the quality of the surveys and in 

 the populations monitored by the surveys. For 

 example, breeding mallards have increased in 

 recent years in the Atlantic Flyway. which is 

 outside the breeding survey area. The breeding 

 survey indicates a stable trend for mallards 

 while the winter survey indicates an increasing 

 trend; the two surveys monitor different portions 

 of the total continental population. 



Five species of diving ducks are monitored 

 by breeding and winter surveys. Because lesser 

 scaup are not distinguished from greater .scaup 

 in the surveys, these species have been com- 

 bined. Breeding populations of diving ducks in 

 1993 were 18% below the 1955-92 average. 

 Redhead and scaup breeding populations were 

 lower than average, whereas the canvasback 

 population was near average, and the ring- 

 necked duck (Aythya collaris) population was 

 above average (Figs. 4, 6). From 1984 to 1993, 

 the breeding population of scaup declined while 

 the breeding population of ring-necked ducks 

 increased (Table). The Midwinter Survey also 

 indicated an increasing population of ring- 

 necks during this period (Table). 



Fourteen species of sea ducks, mergansers, 

 and their allies were monitored by the breeding 

 survey. These 14 species plus the harlequin 

 duck (Histrioniciis histrionicus) were moni- 

 tored during the Midwinter Survey. Because 



10, 



Midwinter Survey 



54 57606366 6972 757881848790 93 

 Year 



Fig. 2. Duck populations in Norlli 

 America. l95.'i-9_^. from ttie 

 Breeding Population and Habitat 

 Survey and the Midwinter .Survey. 



54 57 60 63 66 69 72 75 78 81 84 87 90 93 

 Year 



Fig. 3. Mallard, northern pintail, 

 and green-winged teal breeding 

 population estimates, 1955-93. 



54 57 60 63 66 69 72 75 78 81 84 87 90 9; 

 Year 



Fig. 4. Scaup, blue-winged leal, 

 and gadwall breeding population 

 estimates, 1955-93. 



54 57 60 63 66 69 72 75 78 81 84 87 90 93 

 Year 



Fig. 5. American wigeon and 

 northern shoveler breeding popula- 

 tion estimates, 1955-93. 



