Effects of investigator disturbance on hatching success and nest-site fidelity in a long-lived seabird, Leach’s storm-petrel Alexis L. Blackmer a, *, Joshua T. Ackerman b , Gabrielle A. Nevitt a a Department of Neurobiology, Physiology, and Behavior, University of California, Davis, CA 95616, USA b Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, CA 95616, USA Received 3 September 2002; received in revised form 26 March 2003; accepted 21 April 2003 Abstract Long-lived animals are expected to reduce reproductive effort when breeding conditions are unfavorable, therefore seabirds may be especially sensitive to investigator disturbance. In a non-threatened procellariiform, Leach’s storm-petrel Oceanodroma leu- corhoa, we examined whether the frequency and the time of day of investigator disturbance influenced hatching success, and if disturbance affected hatching success and nest-site fidelity in the subsequent breeding season. Birds used in this study had received little or no investigator disturbance during the prior decade. Hatching success was significantly influenced by the frequency, but not the time of day, of disturbance. Weekly and daily handling of parents reduced hatching success by 50 and 56% compared to the control group. Most failures (91%) were caused by egg desertion, and all the deserted eggs belonged to pairs in the weekly and daily groups. During the subsequent breeding season, the hatching success of disturbed pairs that continued to breed together returned to normal levels. However, 37% more disturbed pairs than control pairs deserted the nesting burrows they had used in the previous year. Since most changes in nest site also result in mate change, investigator disturbance may have had long-term negative effects on reproductive success as well. Our results demonstrate that both weekly and daily investigator disturbance during incubation greatly reduced the hatching success and subsequent nest-site fidelity of naı¨ve Leach’s storm-petrels. # 2003 Elsevier Ltd. All rights reserved. Keywords: Investigator disturbance; Leach’s storm-petrel; Long-lived birds; Egg desertion; Hatching success 1. Introduction Avian taxa are differentially sensitive to investigator disturbance, and these differences likely relate to their life history strategies (Go¨tmark, 1992). Because repro- duction is costly, parents are expected to adjust their level of current investment such that the probability of success justifies the cost to survival and future repro- duction (Williams, 1966; Stearns, 1992). Long-lived iteroparous animals have many opportunities to breed in a lifetime and therefore should take less risk during the current breeding attempt than shorter-lived animals that have a lower potential for future reproduction (Stearns, 1976). Consequently, individuals of long-lived species are more likely to reduce parental effort when breeding conditions are unfavorable and thus may be particularly vulnerable to disturbances caused by researchers. Investigators studying long-lived birds should understand how their research procedures affect their study animals and take precautions to mitigate adverse effects, especially when threatened species are involved. Procellariiforms (e.g., albatrosses, shearwaters, and petrels) are particularly long-lived seabirds, many of whose populations are in decline (Warham, 1990). Many populations are declining because their island breeding habitat is being lost or degraded as a result of human development and the introduction of mamma- lian predators (Warham, 1990). Procellariiforms are further threatened by high levels of mortality incurred in long-line fisheries (Cooper, 2000; Tuck et al., 2001). Investigator disturbance that reduces reproductive suc- cess could exacerbate these population declines and interfere with the accurate assessment of demographic parameters and appropriate allocation of management resources (Croxall and Rothery, 1991; Rodway et al., 0006-3207/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0006-3207(03)00185-X Biological Conservation 116 (2004) 141–148 www.elsevier.com/locate/biocon * Corresponding author. Tel.: +1-530-754-9500; fax: +1-530-752- 5582. E-mail address: alblackmer@ucdavis.edu (A.L. Blackmer).