FACTORS ASSOCIATED WITH DUCK NEST SUCCESS IN THE PRAIRIE POTHOLE REGION OF CANADA

Populations of some dabbling ducks have declined sharply in recent dec ades and information is needed to understand reasons for this. During 1982-85, we studied duck nesting for 1-4 years in 17 1.6 by 16.0-km, h igh-density duck areas in the Prairie Pothole Region (PPR) of Canada, 9 in parkland and 8 in prairie. We estimated nest-initiation dates, ha bitat perferences, nest success, and nest fates for mallards (Anas pla tyrhynchos), gadwalls (A. strepera), blue-winged teals (A. discors), n orthern shovelers (A. clypeata), and northern pintails (A. acuta). We also examined the relation of mallard production to geographic and tem poral variation in wetlands, breeding populations, nesting effort, and hatch rate. Average periods of nest initiation were similar for malla rds and northern pintails, and nearly twice as long as those of gadwal ls, blue-winged teals, and northern shovelers. Median date of nest ini tiation was related to presence of wet wetlands (contained visible sta nding water), spring precipitation, and May temperature. Length of ini tiation period was related to presence of wet wetlands and precipitati on in May, June temperature, and nest success; it was negatively relat ed overall to drought that prevailed over much of Prairie Canada durin g the study, especially in 1984. Mallards, gadwalls, and northern pint ails nested most often in brush in native grassland, blue-winged teals in road rights-of-way, and northern shovelers in hayfields and small (<2 ha) untilled tracts of upland habitat (hereafter called Odd area). Among 8 habitat classes that composed all suitable nesting habitat of each study area, nest success estimates averaged 25% in Woodland, 19% in Brush, 18% in Hayland, 16% in Wetland, 15% in Grass, 11% in Odd ar ea, 8% in Right-of-way, and 2% in Cropland. We detected no significant difference in nest success among species: mallard (11%), gadwall (14% ), blue-winged teal (15%), northern shoveler (12%), and northern pinta il (7%). Annual nest success (pooled by study area and averaged [unwei ghted] over all study areas) was 17% in 1982, 15% in 1983, 7% in 1984, and 14% in 1985. We estimated that predators destroyed 72% of mallard , gadwall, blue-winged teal, and northern shoveler nests and 65% of no rthern pintail nests. In prairie, average nest success decreased about 4 percentage points for every 10 percentage points increase in Cropla nd, suggesting that under conditions of 1982-85, local populations of these species probably were not stable when Cropland exceeded about 56 % of available habitat. We found recent remains of 573 dead ducks duri ng 1983-85; most were females (Anas spp.) apparently killed by predato rs. In some years, mallards and northern pintails were more numerous a mong dead ducks than we expected. More females than males were found d ead among mallards and northern shovelers, suggesting higher vulnerabi lity of females. Of factors we examined, nest-success rate appeared to be the most influential factor in determining mallard production. Nes t success varied both geographically and annually.