The Auk 111(4):945-952, 1994 EFFECTS OF OLFACTORY CUES ON ARTIFICIAL-NEST EXPERIMENTS CHRISTOPHER J. WHELAN, MICHAEL L. DILGER,DAVE RONSON, NATHALIE HALLYN, AND STEVEN DILGER The Morton Arboretum, Lisle, Illinois 60532, USA ABSTRACT.--We examined the effectsof two potential olfactory cueson the outcomeof experiments using artificial nests to assay predationon open-cup nestingsongbirds. In two experiments lasting15 days each and replicated two times at three sites, bamboo nests baited with Japanese Quail (Corturnixjaponica) eggs were placed on the groundin a 5 x 4 grid array with 50 m between adjacent nests. Egg survivorship was monitored every five days, and remotecameras were usedto take photographs of animalsremoving bait eggsfrom nests. One experiment consisted of four treatments that varied the type and amount of olfactory informationprovidedby the investigator: (1) human scent; (2) "no scent"; (3) "deer scent"; and (4) perfume. Artificial scents were applied to shoes, clothing,and skin during the ex- perimentset-up and monitoring.For the first experiment, rates of nestloss 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 treatmentsthan deer-scent and no-scenttreatments regardless of spatial/temporal replicate. The second experiment consisted of two treatments, one in which eggs were replaced periodically, and the otherin which eggs were not replaced for the duration of the experiment.Both treatments had similar ratesand 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 areaof artificialnests, but that either rain or scents (e.g. the deer scent) canbe used to decrease this potential bias.In contrast, changing egg qualities over the time scale of our experiments do notprovide additional cues to predators. Received 20April1992, accepted 25 November 1992. ALTHOUGH NEST PREDATION haslong been rec- ognized as a major sourceof reproductive fail- ure in bird species (e.g. Ricklefs 1969),only re- cently hasnestpredation been hypothesized to be an important determinant of bird commu- nity structure (Martin 1988a, b). Predation on eggsand nestlingsmay regulate bird popula- tions (George1987),influence habitat selection (Blancherand Robertson 1985), and affect pat- ternsof nestdispersion and species coexistence (Martin 1988a,b). Perhapsmore importantly, nest predation also may be important for the conservation of many bird species (Ambuel and Temple 1983, Wilcove 1985). In the increasingly fragmentedlandscapes of North America, nest predation may be an important contribution to population declines of many open-nesting bird species, particularly long-distance Neotropical migrants (e.g. Terborgh 1989). One major methodological problem in stud- ies of nest predation is finding enough nests of a given bird species to have meaningful sample sizes and to controlpossibly confoundingvari- ables (e.g. see Reitsmaet al. 1990). Largely be- causeof these methodologicaldifficulties, in- vestigators have been using artificial nests bait- ed with quail eggs and have measured egg sur- vivorship over someperiod of time simulating a normal incubation period (e.g.Andersson and Wiklund 1978, Loiselle and Hoppes 1983, Wil- cove 1985, Martin 1987, Yahner 1989, Reitsma et al. 1990). Despite the growing useof artificial nests and the admission that some results from using these nests do not mimic results from real nests (e.g.Reitsma et al. 1990, S.A. Temple pers. comm.), few studies have examined in detail methodological issues involving the use of ar- tificial nests. Martin (1987), for instance, re- ported that artificial wicker-basket nests had lower rates of nest predation than artificially baited real nests when both nest types were placed off the ground,but that artificial and real nests had similarrates of predation when placed on the ground. He concluded that the off-ground nests are found primarily by visual-searching predators andthatthese predators possibly avoid 945