Predation of Artificial and Real Arctic Loon Nests in Sweden

Abstract

We examined whether artificial arctic loon (Gavia arctica) nests could be used to estimate predation rates on real unattended nests. In 1983 and 1984, only 3 (9%) of 34 artificial nests were preyed upon within 4 hours after they were laid out. However, if predators memorized the location of real nests and returned to prey upon unattended nests, use of artificial nests could be misleading because predators would not be aware of them. Nevertheless, only 1 of 20 nesting loon pairs was exposed to such a specialist predator (hooded crow, Corvus corone). Predation rates of artificial and unattended real nests appeared to be similar; only 2 (3%) of 77 incubation interruptions of ?<1 hour led to nest predation. Thus, short disturbances of incubating arctic loons rarely led to nest failure, and protection of nest sites may be necessary only at a high frequency of disturbance. J. WILDL. MANAGE. 54(3):429-432 Several species of loons (Gavia spp.) are susceptible to human disturbance (Andersson et al. 1980, Titus and VanDruff 1981, McIntyre 1988). Loons seem to avoid nesting on shores near human activity (Heimberger et al. 1983). Moreover, if they are disturbed during incubation, they may leave the nest for considerable periods (G6tmark et al. 1989), exposing eggs to predators or extreme temperatures. Fifty percent or more of loon nests may be depredated (Titus and VanDruff 1981, Enquist 1983, G6tmark et al. 1989). Because predation is rarely observed, it is difficult to determine the importance of human disturbance. In Sweden, the arctic loon is considered susceptible to human disturbance and in need of protection. However, the choice of management alternatives (e.g., appeals on signboards, sanctuaries comprising single islands or whole lakes) requires information on the timing of predation on nests from which adults are flushed. Artificial nests are often used to study predation rates (Sullivan and Dinsmore 1990). One problem with the technique is that nest preda ors may be aware of the location of real nests but not artificial nests (McIntyre 1988:24, 174). If the target species is larger or more aggressive than the nest predator, it will usually be able to deter the predator (Morse 1974, Sedinger 1990). However, the predator could memorize the nest site and return to it when the adult is off the nest (Enquist 1983). If predators behave this way, use of artificial nests to estimate predation on real, unattended nests may be misleading. On the other hand, if predators find nests by random or systematic search, artificial nests and unattended real nests should be equally vulnerable. In our study, we examined whether artif cial nests could be used to estimate predation rates of unattended arctic loon nests. In addition, we watched real, unattended nests to study the search behavior of nest predators. Our study was funded by the provincial conservation authorities in Viinersborg, Sweden, the University of Gothenburg, and the Swedish Natural Science Research Council; S. A. Rohwer This content downloaded from 157.55.39.35 on Mon, 29 Aug 2016 05:06:45 UTC All use subject to http://about.jstor.org/terms 430 PREDATION OF LOON NESTS * Gotmark et al. J. Wildl. Manage. 54(3):1990 and the Burke Museum, University of Washington, provided office space. We thank R. Alvo, R. D. Elliot, M. Enquist, W. M. Jackson, B. Young, and P. I. Strong for suggesting improvements in the manuscript.