Pollet et al.: Migration of Leach’s Storm Petrels 53 MIGRATION ROUTES AND STOPOVER AREAS OF LEACH’S STORM PETRELS OCEANODROMA LEUCORHOA INGRID L. POLLET1,2*, ROBERT A. RONCONI1,3, MARTY L. LEONARD2 & DAVE SHUTLER1 1Department of Biology, Acadia University, Wolfville, NS B4P 2R6, Canada *([email protected]) 2Department of Biology, Dalhousie University, Halifax, NS B3H 4R2, Canada 3Environment Canada, Canadian Wildlife Service, 45 Alderney Dr., Dartmouth, NS B2Y 2N6, Canada Received 17 June 2003, accepted 04 November 2003 ABSTRACT POLLET, I.L., RONCONI, R.A., LEONARD, M.L. & SHUTLER, D. 2019. Migration routes and stopover areas of Leach’s Storm Petrels Oceanodroma leucorhoa. Marine Ornithology 47: 53–63. Little is known about the movements of small seabirds during migration, but such information is important for their conservation. Leach’s Storm Petrel Oceanodroma leucorhoa is the most abundant seabird in Atlantic Canada, but its population has declined in recent years. Here, we describe trans-equatorial and trans-Atlantic migration movements of 13 Leach’s Storm Petrels, which were tracked with geolocators from two breeding colonies in Nova Scotia, Canada: Bon Portage Island and Country Island. Our results indicate that Leach’s Storm Petrels have low migratory connectivity and that they use multiple stopover areas and overwintering destinations. Birds with stopover areas at higher latitudes overwintered in the North Atlantic Ocean, either in areas associated with the North Equatorial Current or in waters off Newfoundland and Labrador. Birds with lower-latitude stopover areas overwintered in the South Atlantic Ocean, in areas associated with the Benguela Current off southwestern Africa. We observed greater δ15N values (indicating higher trophic level) in feathers from birds that migrated south compared to birds that stayed in the Northern Hemisphere, but we observed no difference in δ13C (which may be interpreted in multiple ways). Species distribution modelling using remotely sensed oceanographic data indicated that high sea surface temperatures and high chlorophyll a concentrations were important predictors of habitat use in winter. Key words: geolocator, Leach’s Storm Petrel, migration, Oceanodroma leucorhoa, seabird tracking, species distribution modelling, stable- isotope analysis INTRODUCTION tracking devices were too large to be carried by these species. However, due to recent miniaturization of data loggers, it is now Seabirds are exposed to threats both in their terrestrial nesting and possible to track smaller species (van der Winden et al. 2014). marine foraging environments (Croxall et al. 2012). These threats Leach’s Storm Petrels Oceanodroma leucorhoa are small seabirds can lead to lower breeding success, mortality, and, ultimately, (~ 45 g) that breed throughout temperate zones in the Northern population declines. Terrestrial threats, including the introduction of Hemisphere. Populations at many colonies in the western North mammalian predators to remote breeding islands, habitat loss, and Atlantic have declined in the past 50 years, and some colonies extreme climatic conditions during the breeding season (Regehr et al. have been abandoned (Robertson et al. 2006, Wilhelm et al. 2015, 2007, Cadiou et al. 2010, Ratcliffe et al. 2010, Ropert-Coudert et al. BirdLife International 2016, Hedd et al. 2018). Despite extensive 2015), are relatively easy to identify and monitor. In contrast, seabirds knowledge of the breeding biology and dietary requirements can face many at-sea threats that are more difficult to ascertain. of Leach’s Storm Petrels (Ricklefs et al. 1987, Stenhouse & Some of these threats include a limitation of food resources due to Montevecchi 2000, Hedd et al. 2009), relatively little is known climate change (Jenouvrier et al. 2003, Grémillet & Boulinier 2009, about 1) their at-sea movements, either during the breeding season Borstad et al. 2011), bycatch from and competition with fisheries or during migration to and from wintering areas (Gaston et al. 2008, (Tasker et al. 2000, Tuck et al. 2011), pollution (Provencher et al. Bicknell et al. 2014, Pollet et al. 2014a, c) and 2) whether their 2015), and off-shore industries (Ronconi et al. 2015). Knowing diet varies with latitude and wintering area. This information is how seabirds use their marine environment is vital for identifying crucial for understanding how year-round conditions influence the important at-sea habitats and for understanding factors influencing population dynamics of this species. population dynamics. For example, stopover areas are important because birds presumably use these areas to replenish body reserves Banding recoveries of Leach’s Storm Petrels from Atlantic Canada after energetically demanding breeding seasons or to await favourable indicate that they spend time in the North Atlantic Ocean during weather before moving to other locations (Murray et al. 2003, the non-breeding season (Gaston et al. 2008, Pollet et al. 2014b), Guilford et al. 2009, Egevang et al. 2010, Jessopp et al. 2013). but at-sea sightings also indicate movement to waters of the Therefore, it is essential to know a species’ key marine regions to Southern Hemisphere (Camphuysen 2007). These observations do understand phenological threats and stressors and to develop effective not, however, provide information on stopover locations, specific conservation and management strategies. wintering areas, migration routes, or provenance of birds observed at sea. A recent study using geolocators on two individuals provided Until recently, little was known about the at-sea habitat requirements preliminary information about Leach’s Storm Petrel locations of small seabirds (< 100 g) outside of the breeding season, because and habitat associations during migration (Pollet et al. 2014a). Marine Ornithology 47: 53–63 (2019) 54 Pollet et al.: Migration of Leach’s Storm Petrels This study confirmed the presence of Leach’s Storm Petrels in to detect a switch of partner without disturbing incubating adults the North Atlantic during the non-breeding season, over warm that had already been processed. Thus, incubating pairs were not and deep waters. However, the study was limited by the small disturbed more than twice (Blackmer et al. 2004). After hatch and sample size, and it did not provide information on stopover areas. until fledging, chicks were measured weekly for weight, tarsus The objectives of the current study were 1) to define stopover length, and wing chord. locations and refine information on both timing of migration and overwintering destinations, 2) to determine if stable-isotope On Country Island, we annually monitored 80 numbered burrows analysis can differentiate overwintering latitudes and trophic in a similar manner. Birds were banded, and we took morphometric niche separation among migration strategies, and 3) to describe measures as above. However, time constraints prevented us from habitat characteristics on the wintering grounds and the resulting measuring chicks on a regular basis, and second adults were distribution of the species. captured and identified less frequently. METHODS All animal handling procedures were approved by the Acadia University Animal Care Committee (Protocol #06-09). Study species and sites Geolocator attachment Leach’s Storm Petrel is a small, sexually monomorphic procellariiform that breeds in the Northern Hemisphere (Huntington et al. 1996). In To track year-round movements, we deployed geolocators (Global eastern North America, these birds arrive at breeding colonies in Location Sensors, GLS) on randomly selected adults within our early May, and females lay a single egg in a burrow in June or July. working plots during the late stages of incubation. Adults were of Incubation lasts approximately 45 days and is performed by both unknown sex and age, and we tagged only one adult per burrow. parents, alternating duties every three to six days. After several days We deployed a total of 65 GLS on Bon Portage Island over four of brooding, chicks are fed by both parents for 50–60 days and fledge breeding seasons and 15 GLS on Country Island during the 2013 at about 65 days post-hatch; the adults depart the colony by end of season (Table 1). September or early October (Huntington et al. 1996). Our study was conducted on Bon Portage Island, Nova Scotia (2012–2016) and We used GLS tags (MK5740, Biotrack, Cambridge, UK) that on Country Island, Nova Scotia (2013–2014). Bon Portage Island weighed 0.9 g and measured 21.9 × 7.9 × 3.8 mm. Each tag was (43°28′N, 065°44′W) is located off the southern tip of Nova Scotia attached to the back of a bird with two subcutaneous sutures, and is the largest Leach’s Storm Petrel colony in the province. The as described in Pollet et al. (2014a); attachment took less current estimate of 39 000 breeding pairs is based on a 2016 survey than 10 minutes per bird, and adults were returned to their burrows and represents a 20 % decline since the previous survey in 1998 immediately following attachment. The total mass of a tag with (Oxley 1999, Pollet & Shutler in press). Country Island (45°06′N, attaching material was 1.1 g, which is below the accepted 3 % 061°32′W) is located off the Eastern Shore region of Nova Scotia, rule (Phillips et al. 2003). The average mass (± standard deviation and a 2013 survey estimated the breeding population at around 11 900 (SD)) of adult Leach’s Storm Petrels in 2013 was 46.5 ± 3.4 g pairs (Environment and Climate Change Canada, unpubl. data). The (n = 22) and 46.7 ± 3.1 g (n