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B.3-2: Assessment of Predator Reduction on Nest Success of Over-water Nesting Ducks

Presented by Michael K. Johnson - Email: joh07575@umn.edu

Although numerous studies have demonstrated that lethal predator management improves nesting success of upland nesting waterfowl, less is known about its potential effect on over-water nesting species. We assessed daily nest survival rates of over-water nesting ducks in the Prairie-Parkland region of southwestern Manitoba during 2015-2017. Professional trappers removed known waterfowl nest predators in addition to focused efforts targeting raccoon (Procyon lotor), American mink (Neovison vison), and corvids (Corvus corax, Corvus brachyrhynchos, Pica hudsonia), between the months of March and July when local breeding occurs. Three 65-km2 study sites were subjected to intensive trapping whereas three equally-sized but untrapped sites served as controls. We located and monitored 504 canvasback (Aythya valiseneria), 422 American redhead (Aythya americana) nests, and 747 over-water nests of other species, including lesser scaup (Aythya affinnis), ring-necked duck (Aythya collaris), ruddy duck (Oxyura jamaicensis), and mallard (Anas platyrhynchos). We compared daily survival rates, estimated using Shaffers logistic-exposure method, between treatment and control sites to assess the effect of predator reduction on nest success. We found no biologically significant effect of trapping when nest success was compared between treatment and control sites. Temporal effects such as initiation date and nest age were important predictors of daily survival rates, and the installment of infrared trail-cameras at nest-sites to identify predators had a positive effect on daily survival rates, which waned as nest age increased. Failure to document a treatment effect on nest success was unexpected and indicates that in comparison to upland systems, targeted trapping efforts were ineffective at removing the most detrimental predator species for the over-water nesting guild.
Session: Threat Mitigation (Tuesday, August 27, 13:20 to 15:00)