Experimental evidence that nesting ducks use mammalian urine to assess predator abundance

Nest predation is a major cause of reproductive failure for many birds; as a consequence, birds that can assess the abundance of predators and avoid nesting where they perceive predation risk to be high should be favored. For dabbling ducks, mammals are important predators on nests and incubating females. Many mammals use urine for marking territories. Because ducks may be able to detect mammalian urine either by ultraviolet light reflectance or by odor, we hypothesized that ducks may be able to assess the abundance of mammalian predators from their urine and thereby avoid nesting where mammals are abundant. We simulated increased predator abundance on experimental plots by using Red Fox (Vulpes vulpes) urine to make artificial scent marks and used water in a similar fashion on control plots. On 16 pairs of plots over 2 years, fewer ducks nested on experimental plots than on control plots (97 vs. 143 nests). These results suggest that birds can assess predator abundance and use the information to choose where to nest. Received 10 March 2012, accepted 21 August 2012.