Effects of Olfactory Cues on Artificial-Nest Experiments

Abstract

We examined the effects of two potential olfactory cues on the outcome of experiments using artificial nests to assay predation on open-cup nesting songbirds. In two experiments lasting 15 days each and replicated two times at three sites, bamboo nests baited with Japanese Quail (Corturnix japonica) eggs were placed on the ground in a 5 x 4 grid array with 50 m between adjacent nests. Egg survivorship was monitored every five days, and remote cameras were used to take photographs of animals removing bait eggs from nests. One experiment consisted of four treatments that varied the type and amount of olfactory information provided by the investigator: (1) human (2) no scent; (3) scent; and (4) perfume. Artificial scents were applied to shoes, clothing, and skin during the ex- periment set-up and monitoring. For the first experiment, rates of nest loss were greater for the human-scent treatment than deer-scent and/or no-scent treatments in one-half of the spatial/temporal replicates. Rain appears to have complicated the effects of the scent treat- ments in some of the spatial/temporal replicates. Final levels of nest loss, however, were greater for perfume and human-scent treatments than deer-scent and no-scent treatments regardless of spatial/temporal replicate. The second experiment consisted of two treatments, one in which eggs were replaced periodically, and the other in which eggs were not replaced for the duration of the experiment. Both treatments had similar rates and final levels of nest loss. Approximately 90% of 51 photographs were of olfactory-searching, predominantly noc- turnal mammals. We conclude that olfactory-searching predators can cue on human odors left in the area of artificial nests, but that either rain or scents (e.g. the deer scent) can be used to decrease this potential bias. In contrast, changing egg qualities over the time scale