Using GPS data loggers to characterize habitat use of Rhinoceros Auklets (Cerorhinca monocerata) at the Farallon Islands during 2014

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1 Using GPS data loggers to characterize habitat use of Rhinoceros Auklets (Cerorhinca monocerata) at the Farallon Islands during 2014 Report to the U.S. Fish and Wildlife Service Farallon National Wildlife Refuge December 2014 P. Warzybok and R.W. Bradley California Current Group Point Blue Conservation Science 2014 Point Blue Conservation Science

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3 2014 SEFI RHAU GPS Report P a g e 2 Using GPS data loggers to characterize habitat use of Rhinoceros Auklets (Cerorhinca monocerata) at the Farallon Islands during 2014 December 2014 Point Blue Conservation Science Pete Warzybok and Russell W. Bradley Acknowledgements We would like to thank Dr. Scott Shaffer for supplying the GPS loggers, training staff and providing technical support on this pilot study. We are also indebted to Point Blue volunteer research assistants Julie Howar, Kiah Walker, Katherine Jackson and Robert Snowden, who assisted with checking nest boxes at all hours of the night. Suggested Citation Warzybok, P. and R.W. Bradley Using GPS data loggers to characterize habitat use of Rhinoceros Auklets (Cerorhinca monocerata) at the Farallon Islands during Unpublished report to the U.S. Fish and Wildlife Service. Point Blue Conservation Science, Petaluma, California. Point Blue Conservation Science Contribution Number Point Blue Conservation Science Point Blue s 140 staff and seasonal scientists conserve birds, other wildlife and their ecosystems through scientific research and outreach. At the core of our work is ecosystem science, studying birds and other indicators of nature s health. Visit Point Blue on the web Cover photo credit/caption: Rhinoceros auklet in nest box by P. Warzybok

4 2014 SEFI RHAU GPS Report P a g e 3 Table of Contents LIMITED RIGHTS DISCLOSURE... 4 INTRODUCTION... 5 METHODS... 6 RESULTS... 7 CITATIONS FIGURES... 12

5 2014 SEFI RHAU GPS Report P a g e 4 LIMITED RIGHTS DISCLOSURE All data contained in this 2014 Rhinoceros Auklet GPS Study Report ( report ) is the copyright of Point Blue Conservation Science (formerly PRBO) and collected in coordination with the USFWS, Farallon National Wildlife Refuge under the terms of Cooperative Agreement # 81640AJ008. The Government's rights to use, modify, reproduce, release, perform, display, or disclose the data set forth in this report are restricted by section 36(a) of OMB Circular A-110 Uniform Administrative Requirements for Grants and Agreements With Institutions of Higher Education, Hospitals, and Other Non-Profit Organizations as incorporated in the above identified contract. Any reproduction of data or portions thereof, in this report must also reproduce this Limited Rights Disclosure and all copyright markings. Requests to distribute, use, modify, reproduce, release, perform, display, or disclose data, or portions thereof, in this report beyond the scope of the government s license, must be submitted to Point Blue Conservation Science at the referenced address. Any reference to or use of this report, or any portion thereof, within the scope of the government s license, shall include the following citation: Warzybok, P. and R.W. Bradley Using GPS data loggers to characterize habitat use and foraging behavior of Rhinoceros Auklets (Cerorhinca monocerata) at the Farallon Islands during Unpublished report to the U.S. Fish and Wildlife Service. Point Blue Conservation Science, Petaluma, California. Point Blue Conservation Science Contribution Number Outside the scope of the government s license, this report shall not be used without written permission from the director of the California Current Group at marinedirector@pointblue.org or Point Blue Conservation Science, 3820 Cypress Drive #11, Petaluma, CA,

6 2014 SEFI RHAU GPS Report P a g e 5 INTRODUCTION Knowledge of the interactions between marine birds and their environment can be critical for understanding trends in their populations, determining potential stressors, understanding ecosystem health and for informing effective management, including the establishment and evaluation of Marine Protected Areas (Maxwell et al. 2013). Marine birds are top predators and as such integrate the effects of changes in the system at all trophic levels below them. Rhinoceros auklets are wide ranging top predators and as such may be exposed to varying environmental risk factors due to differences in foraging locations, prey selection and behaviors. Much is known about the breeding biology of these birds when they are at the colony but far less is known about their lives at sea, and there is a need to establish the mechanistic relationships linking these predators to their environment. Rhinoceros auklets are piscivorous diving predators that feed on rockfish (Sebastes spp.), saury (Cololabis saira), anchovies (Engraulis mordax) and other small forage fishes in central California (Thayer and Sydeman 2007, Warzybok et al. 2013); prey species that are typically found both nearshore (anchovies; MacCall 1990) and offshore (saury; Hughes 1973). These studies enable researchers to infer broad scale foraging locations based on the ecology of the prey species captured and to estimate the effects of prey availability and climate conditions on reproductive success (e.g. Hedd et al. 2006; Thayer and Sydeman 2007; Deguchi et al. 2010). However the spatial resolution obtained from this method is poor and current information on prey species distribution is often lacking, thereby presenting an incomplete picture of the foraging ecology of the auklets. Foraging locations and concomitant habitat characteristics determined by GPS-tracking would enable researchers to gain a more complete understanding of the complex foraging ecology of rhinoceros auklets during the breeding season. Previous tracking studies have revealed inter-individual variation in foraging strategies and habitat use among chick-rearing seabirds (e.g. Sooty Shearwater, Puffinus griseus, Shaffer et al. 2009; Great Frigatebirds, Fregata minor, Gilmour et al. 2012). The same may hold true for rhinoceros auklets. Furthermore, foraging strategies may be influenced by morphological size differences between individuals or between the sexes (Mancini et al. 2013). Male auklets are slightly larger than females (Gaston and Dechesne 1996) and a recent study has demonstrated that prey selection may differ between male and female auklets with females appearing to forage on prey species typically found farther offshore (Carle et al. 2014). This suggests at least that males and females may be subjected to different environmental stressors related to their foraging preferences but more detailed studied could potentially confirm this. Although this population of rhinoceros auklets breeds within a Marine Protected Area, it is possible that they forage outside this management area, and thus do not benefit from the full protection that Marine Protected Areas and the Farallon National Wildlife Refuge provide (e.g. Maxwell and Morgan 2013).

7 2014 SEFI RHAU GPS Report P a g e 6 During 2013, we began collaborating with Dr. Scott Shaffer at San Jose State University to examine the foraging behavior of breeding Western Gulls (Larus occidentalis) at the Farallon National Wildlife Refuge using GPS data loggers (see Shaffer and Warzybok 2014 for details). In 2014, we initiated a pilot study to test the efficacy of using the same GPS loggers to examine Rhinoceros Auklet foraging. The objective of this pilot study was to explore linkages between auklet foraging, prey abundance and ocean conditions during the chick rearing period. Our goal was to assess foraging range, habitat use and diet of marked birds while testing our ability to employ these GPS loggers for data collection. Our study was conducted under Special Use Permit from the Farallon National Wildlife Refuge. METHODS We captured adult Rhinoceros Auklets which were brooding young chicks from 4 nest boxes on the Farallon National Wildlife Refuge in order to outfit them with GPS loggers. The original captures were conducted on July 17 (3 birds) and July 18 (1 bird). We only captured birds from boxes which had appropriately aged chicks and which were not part of any other studies. We ended up with a total of 2 males and 2 females this season. For all birds captured, we measured weight and bill depth (to determine sex), recorded their band number and attached the GPS. The GPS loggers (IgotU GT-120, MobileAction Technology, Taiwan), were approximately 44mm x 28 mm in size and weigh 15 grams (less than 3% of auklet body mass). In order to make them smaller and to ensure they would be waterproof, we removed the GPS and battery from its plastic case and encapsulated them in adhesive-lined heat shrink tubing. They were programmed to record GPS coordinates every 30 seconds and were expected to record location data for approximately 6 days. The instruments were attached to the feathers on the bird s back using three strips of Tesa tape (Tesa corp., Charlotte, NC) layered around the base of multiple feathers. Tesa tape is strong, waterproof, and easily removed from feathers upon recovery and has been used successfully in similar applications on many different marine birds. Once the loggers were securely attached the bird was released back into the nest box. We returned to the boxes beginning three nights later and made between 3 and 6 visits each night for 10 days in an attempt to retrieve the loggers. Nest site visits were made between 2145 (shortly after dusk) and 0500 (just before sunrise) at 1-2 hour intervals. One-way flaps, which allowed the adult to enter the box but not get back out, were constructed using heavy cardboard. These were installed on the inside of the nest box entrance tunnels after 3 days of unsuccessful capture attempts in order to decrease the chance of missing a bird that had visited the box to feed the chick and subsequently left again between our site visits.

8 2014 SEFI RHAU GPS Report P a g e 7 RESULTS Recovery and effects of GPS: Retrieval of GPS loggers proved to be difficult and we were only able to recover 1 of the 4 devices deployed. Most birds did not return to the nest box for their expected incubation shifts and the chicks were often left alone. Of the four birds fitted with GPS, one bird returned to the nest box six days after the initial deployment still carrying the logger. Both the logger and the bird were in good condition at the time of the recovery. The Tesa tape was still holding securely to a group of feathers on the bird s back and was removed by gently peeling the tape away. A second bird returned to the nest box 8 days after the deployment but was no longer carrying the logger. The logger and tape had both come off between deployment and recapture. There were no obvious signs of missing feathers or abrasion from having carried the logger suggesting that it had slipped off or fallen off along with a few of the feathers to which it had been secured. The final two birds were not encountered after 10 consecutive nights of searching and are presumed to have abandoned. Due to the need to positively identify which mate was present during nest site visits, the mate of birds carrying the GPS logger were handled frequently. We attempted to mitigate the effects of repeated encounters by handling the mate as little as possible while ascertaining the bird s identity (i.e. quickly checking for logger presence and reading the band number), but this still resulted in individual birds being handled as many as 10 times during this period. Chick Growth As in previous studies using Time-Depth Recorders on Cassin s auklets, we compared chick growth curves between boxes where one adult was fitted with a GPS and control sites where neither adult carried a device. Comparisons were made to chicks of the same approximate age and growth rates were calculated between the ages of 10 and 45 to 50 days using weights obtained at 5 day intervals. We selected this age range because those were the ages for which we had mass measurements from both GPS and control sites (Figure 1). Chicks from the control sites (adults not fitted with GPS) grew at an average of 4.97 grams per day (s.e. = 0.41, n=6) while chicks from GPS logger sites grew at an average of 3.48 grams per day (s.e. = 0.38, n=3; Fig. 2). While chicks fledged from 3 of the 4 GPS, they took longer to fledge and had a lower mean fledging weight. Fledging weights of chicks from GPS sites were lower on average and chicks took longer to fledge than chicks from control sites. The mean fledging weight for chicks from GPS sites was 185g (s.e. = 61.61, n=3) whereas control sites had a mean of 283g (s.e. = 20.06, n=6). Foraging Behavior We were only able to recover one GPS logger. The logger functioned well and collected data points for 6 days over three distinct foraging trips. The GPS tracks indicated that the adult made

9 2014 SEFI RHAU GPS Report P a g e 8 two foraging trips between the island and the shelf break southwest of the island and then one extend trip up in which it first flew in the same direction as the first two trips before continuing well beyond the shelf break and then turning north and flying all the way to Cordell Bank (Figure 2). During that extended trip, the bird spent two nights on the water without returning to the colony. Conclusions and Recommendations: The 2014 pilot study was generally not as successful as we had hoped. Despite a great deal of effort, we were only able to recover one of the GPS loggers we deployed. In addition, all of the birds that were equipped with the loggers demonstrated reduced site attendance, including two birds which appear to have abandoned. Although the sample size is too small to make a statistically meaningful comparison, chicks from sites where one adult was equipped with a logger had, on average, slower growth rates, longer time until fledging and lower fledging weights. This is all likely due to reduced site attendance and consequently fewer feedings from adults equipped with GPS loggers. Overall attendance at these sites was also low with the majority of site visits finding only the chick present, although we did not monitor attendance patterns of birds in non-gps boxes to determine if this was unusual or not. While it is likely that the disturbance caused by capturing birds at the nest box and carrying the GPS tag had some effect on attendance patterns, we believe that other factors may have also contributed to our poor recovery success. We did not attempt this pilot study until late in the breeding season due to permitting requirements and logistical challenges with obtaining the GPS loggers. Although we did not consider that to be an issue at the time of deployment, circumstances suggest it may have been a poor choice. Beginning around mid-july, just prior to logger deployment, ocean conditions around the Farallones changed rapidly. There was an incursion of very warm water into the region with Sea-surface temperature climbing approximately 2 C in about a week. This was accompanied by an overall reduction in prey resources and more importantly, the disappearance of juvenile rockfish which had accounted for 93% of chick diet up to that point in the season. This rapid change in local ocean productivity at the same time we conducted the pilot study likely caused the auklets to have to work harder to find food and consequently spend less time at the nest site. Chick weight data for the chicks in control boxes indicates that although they generally performed better than chicks from GPS boxes, they also lost weight or grew more slowly during this period. Another mitigating factor may have been the age of the chicks when the loggers were deployed. We had hoped to place loggers on birds with very young chicks when we expect both adults to still be taking turns brooding the chick. However, due to the late deployment, our options were limited. Many sites already had chicks that were close to fledging or in some cases had already fledged. Therefore we chose sites with the youngest chicks possible. Of the four boxes we selected for deployment, one had a 5 day old chick, one a 25 day old chick and 2 with

10 2014 SEFI RHAU GPS Report P a g e 9 35 day old chicks (though still relatively small and only partly feathered). The site with the 5 day old chick was the only one where we were able to recover the GPS logger and also the only one where the chick was consistently attended by an adult. Finally, the size and placement of the loggers on the birds may have had an impact. These loggers, while lightweight, are rather large and are not hydrodynamic. They have a square and when attached to the back feathers of a diving bird such as the Rhinoceros Auklet may present a significant drag. These same tags were extremely successful when attached to the tail on Western Gulls, but due to the short tail of the auklets and the need of the logger to be above waterline this attachment method was not practical. Substituting a smaller or differently shaped logger or moving the placement of the logger further down on the bird s back would alleviate some of this issue. Despite the difficulties encountered during this pilot study, we believe that the data returned could prove to be extremely valuable for furthering our understanding of Rhinoceros Auklet foraging behavior and habitat use. Data from the tag we were able to recover showed a very interesting and unexpected pattern and demonstrates that auklets may forage a considerable distance from the island. Given the important information the use of GPS loggers can provide and the environmental factors that contributed to the low recovery rate, we would like to follow up with a second trial study. The second trial would build on what we have learned during this study in an attempt to increase recovery success. We would carefully consider the timing of the deployment, age of chicks and oceanic conditions at the time to maximize success and would further evaluate the potential effects of tagging by monitoring the attendance patterns of non- GPS auklets to determine if environmental conditions or logger effect led to the low attendance observed during the pilot study.

11 2014 SEFI RHAU GPS Report P a g e 10 CITATIONS Carle, R., J. Beck, D. Calleri and M. Hester Temporal and sex-specific variability in Rhinoceros Auklet diet in the central California Current system. J. Mar. Syst. (2014) Deguchi, T., A. Wada, Y. Watanuki, & Y. Osa Seasonal changes of the at-sea distribution and food provisioning in rhinoceros auklets. Ecological Research 25: Gaston, A. J. & S. B. Dechesne Rhinoceros Auklet (Cerorhinca monocerata), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: doi: /bna.212 Gilmour. M. E., E. A. Schreiber, & D. C. Dearborn Satellite telemetry of Great Frigatebirds Fregata minor rearing chicks on Tern Island, north central Pacific Ocean. Marine Ornithology 40: Hedd, A., D. F. Bertram, J. L. Ryder, & I. L. Jones. Effects of interdecadal climate variability on marine trophic interactions: rhinoceros auklets and their fish prey. Marine Ecology Progress Series 309: Hughes, S. E Stock composition, growth, mortality, and availability Pacific saury, Cololabis saira, of the northeastern Pacific Ocean. Fisheries Bulletin 72: MacCall, A. D Dynamic geography of marine fish populations. Washington Sea Grant Program, University of Washington Press, Seattle. 153 pp. Mancini, P. L., A. L. Bond, K. A. Hobson, L. S. Duarte, & L. Bugoni Foraging segregation in tropical and polar seabirds: Testing the Intersexual Competition Hypothesis. Journal of Experimental Marine Biology and Ecology 449: Maxwell, S. M., & L. E. Morgan Foraging of seabirds on pelagic fishes: implications for management of pelagic marine protected areas. Marine Ecology Progress Series 481: Maxwell, S.M., E.L. Hazen, S.J. Bograd, B.S. Halpern, G.A. Breed, B. Nickel, N.M. Teutschel, L.B. Crowder, S. Benson, P.H. Dutton, H. Bailey, M.A. Kappes, C.E. Kuhn, M.J. Weise, B. Mate, S.A. Shaffer, J.L. Hassrick, R.W. Henry, L. Irvine, B.I. McDonald, P.W. Robinson, B.A. Block & D.P. Costa Cumulative human impacts on marine predators. Nature Communications Vol. 4. Shaffer, S. A., H. Weimerskirch, D. Scott, D. Pinaud, D. R. Thompson, P. M. Sagar, H. Moller, G. A. Taylor, D. G. Foley, Y. Tremblay, & D. P. Costa Spatiotemporal habitat use by breeding sooty shearwaters Puffinus griseus. Marine Ecology Progress Series 391:

12 2014 SEFI RHAU GPS Report P a g e 11 Shaffer, S. A. and P. Warzybok Progress Report on Western Gull Foraging at the Farallon National Wildlife Refuge. Unpublished report to the U.S. Fish and Wildlife Service. San Jose State University, San Jose, CA. Thayer, J. A., & W. J. Sydeman Spatio-temporal variability in prey harvest and reproductive ecology of a piscivorous seabird, Cerorhinca monocerata, in an upwelling system. Marine Ecology Progress Series 329: Warzybok, P.M., R.W. Berger and R.W. Bradley Population Size and Reproductive Performance of Seabirds on Southeast Farallon Island, Unpublished report to the U.S. Fish and Wildlife Service. Point Blue Conservation Science, Petaluma, California. Point Blue Conservation Science Contribution Number 1957.

13 2014 SEFI RHAU GPS Report P a g e 12 FIGURES Mean chick weight (g) DAY5 DAY10 DAY15 DAY20 DAY25 DAY30 DAY35 DAY40 DAY45 DAY50 Chick Age Non-GPS GPS Figure 1. Rhinoceros Auklet chick growth rate comparison between GPS sites and control (Non- GPS) sites. The solid line represents the actual data values while the dotted line represents the modeled growth curve. Standard error estimates are also displayed for each point.

14 2014 SEFI RHAU GPS Report P a g e 13 Figure 2. GPS tracks from the Rhinoceros Auklet in box 58 on Southeast Farallon Island between July 17 and 23, 2014.