EFFECTS OF NASAL DISCS ON NESTING BY MALLARDS

Nasal markers (saddles and discs) are used commonly to identify indivi duals in studies of waterfowl ecology. The potential effects that thes e markers have on the study animals has been poorly tested for free-ra nging birds. We examined the effects of nasal discs on several indices of nesting effort for wild Mallards in the prairie pothole region of south-central Canada. Nasal discs did nor significantly influence the proportion of birds that remained on the study area, the proportion of birds that nested, the number of nests initiated per bird, the total number of days a given bird devoted to laying or incubating eggs, or t he proportion of birds that successfully hatched a nest. Compared to u nmarked birds, however, nasal-marked birds did significantly delay the ir first nest by 2-6 days. Investigators should carefully examine stud y objectives before deciding to nasal-mark individuals.