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Nest Searches

Where possible, 2-person teams searched vegetation in upland habitats with chain drags (8-9-mm-diam. by <=80-m-long) towed by vehicles, using procedures similar to those described by Higgins et al. (1969). Where chain drags could not be used effectively, persons walked and pulled rope drags or used switches to beat the vegetation and flush nesting females. We searched most habitat suitable for nesting on prairie study areas where there were few trees. In parkland, trees and shrubs prevented use of chain drags in many places. There, to distribute the search effort throughout the study area, we searched completely all nesting habitat in individual quarter-sections or portions of quarter-sections scattered along both sides of the center road. We augmented scanty samples of nests in habitats (mostly Wetland, Right-of-way, and Odd area) on some study areas (n = 20 area-years) by searching a few sites (mean = 8/area-year) of the same class within 0.8 km of the study area.

We marked each nest with an individually-numbered willow stick (1-1.5 m) flagged with a small piece of pink plastic tape, or noted the nest location in relation to a natural feature (e.g., prominent rock or fence post). Marker sticks were placed upright 4 m from the nest. Nest locations were plotted on aerial photographs. Nests were revisited about every 7-10 days until >=1 egg hatched or the nest was abandoned or totally destroyed. Data recorded upon finding each nest were duck species, date, location, habitat class, type of vegetation within 1 m, number of eggs, and incubation stage (Weller 1956, Klett et al. 1986).

On each revisit to a nest, we verified species identity and recorded date, number of eggs, and completed clutch size (if known). On the last visit we recorded fate and, if the nest failed to hatch, suspected cause of failure. A nest was deemed successful if >=1 egg hatched, as determined by presence of shell membranes (Klett et al. 1986) or ducklings in the nest bowl, and unsuccessful if all eggs were destroyed or missing. If >=1 whole egg remained and the nest was no longer tended (eggs cold and additional eggs not being deposited daily), we classified the nest as abandoned; such nests also were deemed unsuccessful. For nests that appeared to have been abandoned on the day of discovery, we attributed abandonment to investigator influence. For nests that were abandoned after some eggs were destroyed, we attributed abandonment to predator influence. Nest fate was classified as unknown if the nest could not be relocated.

We assigned cause of all nest failures to predation, agricultural equipment, weather, or other (e.g., flooding, fire, trampling); nests that failed because of abandonment (except investigator-influenced) were included in the appropriate category of failure. Cause of nest failure was called unknown if we suspected >1 agent was involved, or if the cause was ambiguous (e.g., nest that appeared to have been destroyed by tillage might have been destroyed by a predator before tillage).

Adult Mortality