Ten Years of Investigating Auklet‐Rat Interactions at Kiska Island, Alaska: Summary of Monitoring from 2001‐2010 Research camp at Tangerine Cove, and the auklet colony on the 1960’s lava dome, June 2010 © ALB Alexander L. Bond*, Erin E. Penney, and Ian L. Jones Department of Biology Memorial University of Newfoundland St. John’s, Newfoundland and Labrador, A1B 3X9, Canada Tel: (709) 864‐8141 Fax: (709) 864‐3018 *E‐mail: [email protected] November 2010 Table of Contents TABLE OF CONTENTS 1 EXECUTIVE SUMMARY 2 INTRODUCTION 3 METHODS 5 AUKLET PRODUCTIVITY 5 TIMING OF BREEDING 6 AUKLET SURVIVAL 7 NORWAY RAT ABUNDANCE AND DISTRIBUTION 9 ADDITIONAL OBSERVATIONS 10 RESULTS 10 LEAST AUKLET PRODUCTIVITY & PHENOLOGY 10 CRESTED AUKLET PRODUCTIVITY & PHENOLOGY 11 LEAST AUKLET SURVIVAL 11 CRESTED AUKLET SURVIVAL 12 NORWAY RAT ABUNDANCE AND DISTRIBUTION 12 DISCUSSION 13 LEAST AUKLET PRODUCTIVITY & PHENOLOGY 13 CRESTED AUKLET PRODUCTIVITY 14 LEAST AUKLET SURVIVAL 16 CRESTED AUKLET SURVIVAL 16 NORWAY RAT ABUNDANCE AND DISTRIBUTION 17 ADDITIONAL OBSERVATIONS 19 CONCLUSIONS AND RECOMMENDATIONS 20 ACKNOWLEDGEMENTS 20 LITERATURE CITED 22 TABLES 26 FIGURES 32 APPENDICES 36 APPENDIX I 36 APPENDIX II 39 1 Executive Summary We quantified productivity and survival of Least and Crested Auklets, and indexed the relative abundance and distribution of Norway Rats, at Sirius Point, Kiska Island, Alaska from May‐August 2010. Overall, Least Auklet productivity (0.66) was high, typical of rat‐ free colonies, and no different than productivity on nearby, rat‐free Buldir Island (0.64). Crested Auklet productivity (0.61) was also similar to Buldir (0.69) in 2009. Survival of Least Auklets from 2008‐2009 (the most recent estimate) was 0.81, an increase on the previous period. Rat abundance, based on our indexing method and general observations, was very low, similar to conditions observed in 2007. Continued monitoring of auklet demography at Kiska is necessary to further quantify natural variability at this large auklet colony and to further understand the effects of rats on Crested Auklets’ breeding biology and demography. Under present conditions and in the absence of immigration from other colonies, the Least Auklet population at Sirius Point is expected to decline rapidly over the next two decades. 2 Introduction The large auklet (Aethia spp.) colony at Sirius Point, Kiska Island, Aleutian Islands, Alaska (52°08’N, 177°37’E), has over a million Least (Aethia pusilla) and Crested Auklets (A. cristatella) and covers more than 1.8 km2 in area (Jones et al. 2001; Byrd et al. 2005). Due to the enormous numbers present, and spatial extent of the colony, estimating, or even observing, population‐level effects of introduced predators is a difficult proposition. Norway rats (Rattus norvegicus) were introduced to Kiska during the military occupations of 1942‐1946 (Murie 1959), have extirpated several bird species from the island, and likely present a long‐term threat to the remaining breeding seabirds on the island, including auklets (Major et al. 2006; Major et al. submitted). This was our tenth year of monitoring auklet demography, and our fifth year of monitoring rat abundance and distribution at Kiska. Our cumulative observations have shown that when rat abundance is high, auklet productivity is low (e.g., the years 2001‐2002), but rat abundance has been, for some unknown reason, highly variable and unpredictable among years, and very low for the last few years. A quantitative method of indexing rat abundance was devised (Eggleston et al. in prep) and implemented at Sirius Point in 2006 (Eggleston and Jones 2006), refining our ability to correlate rat activity with auklet population parameters. Nevertheless, only long‐term demographic monitoring and modelling will indicate whether auklets and rats are in stable coexistence at Kiska. Sirius Point is a critical breeding site for auklets because it contains the largest patch of available auklet breeding habitat in the Aleutians in the form of a 45‐year‐old 3 lava dome (Coats et al. 1961; Simkin et al. 1981). It is also home to about 5% of the global Least Auklet and Crested Auklet populations (Gaston and Jones 1998) and is perhaps the largest Least Auklet colony in the Aleutian Islands (Byrd et al. 2005). Understanding the population dynamics of auklets in relation to rats is therefore critical to their successful management and conservation in Alaska. The objectives of our overall study were to: 1) Quantify Least and Crested Auklet productivity from representative areas of the Sirius Point colony for the 2010 breeding season, 2) Identify causes of auklet breeding failure (especially if involving rats), 3) Quantify Least Auklet annual adult survival at one representative study plot for 2001‐2009 from resightings of previously colour‐marked birds in 2010 (again assessing possible effects of rats), and 4) Redeploy a rat monitoring transect protocol to quantify inter‐year variation in relative abundance of rats at Sirius Point. In addition, we are also conducting detailed analysis of diet, moult and general biology of auklets as well as diet of rats, although these analyses are ongoing and will be presented elsewhere. 4 Methods Auklet Productivity Least and Crested Auklet productivity was measured at Sirius Point, Kiska Island using established methods (Fraser et al. 1999; Major et al. 2006; Bond et al. submitted) that have been employed consistently since 2001. In short, we visited breeding sites every 4‐7 days, and determined their status (empty, egg, chick, adult, unknown). We considered sites active when we found an adult on two consecutive visits, or we saw an egg. We scored sites as successful in fledging a chick if the chick disappeared after 25 days (Least Auklets, Roby and Brink 1986) or 26 days (Crested Auklets, Fraser et al. 1999). We defined reproductive success as the proportion of active nests from which chicks fledged. We used apparent estimates of reproductive parameters (chicks fledged per pair) rather than a Mayfield‐corrected estimate since we were interested in the relative measures of reproductive performance, not absolute estimates (Johnson 2007). We also assumed that any biases created by using apparent estimators were consistent across all years. Furthermore, Major et al. (2006) found that Mayfield estimates for Least Auklet productivity at Kiska Island from 2001‐2003 did not differ from uncorrected estimates as presented here. We began searching for active nests within 3‐4 days in any given year, and so effects of left truncation, or the inability to detect nests that failed prior to the first visit (Johnson 2007), would be uniform across the study. Similarly, a single criterion was used to infer successful fledging, meaning that differences in reproductive success reported here were not due to methodological differences. 5 Any failed crevice was examined closely to determine the cause of failure, including whether rat predation was responsible. These data were compared to similar data collected at the auklet colony at Main Talus, Buldir Island (52°23’N, 175°55’E) using the same protocol. Buldir has no rats, its colony is only about 100 km from the colony at Sirius Point, and thus provides a useful comparison to Sirius Point in determining the effect of rats on auklet productivity. Previously (2001‐2007), our auklet productivity data were compared to those from Kasatochi Island (52°11’N, 175°31’W), but the volcanic eruption at Kasatochi in August 2008 ended auklet monitoring there (Smith et al. 2010; Williams et al. 2010). At Kiska, we used three plots to estimate productivity at Sirius Point (New Lava, Old Lava Low and Old Lava High), and these are believed to be representative of the auklet colony at present (Jones et al. 2001, Major et al. 2006). IN 2010, we also established a new plot on the old lava flow above camp to monitor Crested Auklet nests; these data have been included in the Old Lava High plot. We used a binomial generalized linear model with a logit link in SPSS 16 (SPSS Inc., Chicago, IL, USA) to examine differences among plots and between islands (Bond et al. submitted). Values were considered significant when p < 0.05. Timing of Breeding We estimated date of hatching for a sample of Least Auklet nests. We included only nests that we scored as an egg on one visit, and as a chick on the very next (4‐7 days later), and we assumed hatching date to have occurred at the midpoint between 6 the two visits. Again, these data were compared to both long‐term data from Kiska and Buldir islands. Analysis of variance (ANOVA) was used to test for differences among plots on Kiska, and between Buldir and Kiska islands. Auklet Survival A population of marked Least and Crested Auklets of unknown age was established on a single plot on the 1964 lava dome in 2001 (Jones et al. 2001) A capture‐mark‐resighting protocol to measure annual survival on this study plot has been employed each year (2001‐2010). Birds were captured on the 50 m2 plot using noose carpets and adults and were marked with a uniquely‐numbered metal band and combination of Darvik colour bands (Jones et al. 2002; Jones et al. 2004). We did not colour‐band subadults (two‐year‐old individuals, identified using criteria in Bédard and Sealy (1984) as having worn, brown flight feathers and foreheads), and they were not included in the analysis. We resighted colour‐marked auklets during their main activity periods (0900‐1500 and 2200‐0030 Hawaii‐Aleutian Standard Time) from late May to early August each year, encompassing the entire breeding cycle. Using procedures described in Lebreton et al. (1992), annual probabilities of survival (φ) and resighting (p) were generated using Program MARK (White and Burnham 1999). Because our capture technique captures both breeding and non‐breeding individuals, some individuals are never seen again after marking (Jones et al.