Demographics of Breeding Female Mallards in Southern Ontario, Canada

Abstract

Reliable estimates of breeding-ground demographic rates are needed to develop effective conservation strategies for mallard (Anas platyrhynchos) breeding habitat in eastern North America. We radiomarked 224 female mallards in an agricultural landscape in southern Ontario, Canada, during 1997–2000. At each of 4 sites, 1 during each year, we estimated survival of adult females, breeding incidence, nesting effort, clutch size, nesting habitat use, nest survival, and hen success. We also examined the influence of nest age, date, and habitat on nest survival and the influence of date and female age on survival of adult females. Almost all females remaining on site were observed to initiate ≥1 nest (x̄ = 0.97, range = 0.95–0.98), we detected a mean of 2.07 (1.80–2.36) nests per female each season, and full clutch size averaged 9.56 (9.1–10.0). For most sites, females nested in grassland and hay land more than expected relative to habitat abundance, nested in wetlands and woody habitats in proportion to abundance, and avoided cropland and developed areas. Survival of adult females from 25 March to 15 July averaged 0.75 (0.65–0.84). Estimates from our best model showed relatively uniform survival across the breeding season, with the exception of large decreases for 2 sites during the peak of the onset of hay cutting. Nest survival averaged 0.13 (0.11–0.15). Our best model supported increasing survival with nest age but did not include variation relative to habitat or date, except in hay land. Nest survival in hay land was high relative to other habitats early in the nesting season, but declined sharply with the onset of hay cutting. Hen success averaged 0.37 (0.25–0.46). Because estimated nest survival varied little among sites and habitats and because suitable nesting habitat appeared abundant, we suggest that upland habitat conservation will accrue only limited demographic benefits. Incentives to alter hay-cutting practices may decrease mortality of nests and nesting females, but we believe such incentives are unlikely to be cost efficient and that experiments would be needed to reliably assess benefits.