Ingrid L Pollet
email: ipollet@yahoo.com

Ariel K Lenske

Anne Ausems

Christophe Barbraud

Yuliana Bedolla-Guzmán

Anthony W J Bicknell

Mark Bolton

Alexander L Bond

Karine Delord

Antony W Diamond

A N M A Ausems

David A Fifield

Ca Gjerdrum

Luk R Halpin

Erpur S Hansen

April Hedd

R Hoeg

Heather L Major

Ro A Mauck

G Mcclelland

L Mcfarlane Tranquilla

William A Montevecchi

Mike Parker

An M A Ausems

Christop Barbra

Anton W Diamo

Gregory T W Mcclel

Laura Mcfarlane Tranq

Isabeau Pratte

J-François Rail

Greg J Robertson

Jennifer C Rock

Robert A Ronconi

Dave Shutler

Iain J Stenhouse

Akino Takahashi

Yukata Watanuki

Linda J Welch

Sabina I Wilhelm

Sarah N P Wong

Mark L Mallory

Experts' opinions on threats to Leach's Storm-Petrels ( Hydrobates leucorhous ) across their global range

Keywords: expert opinion, Hydrobates leucorhous, Leach's Storm-Petrel, seabird conservation, threats

établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Human activities have grown at unprecedented rates in recent decades, affecting all ecosystems [START_REF] Marques | Increasing impacts of land use on biodiversity and carbon sequestration driven by population and economic growth[END_REF][START_REF] Baud | Global acceleration of lake sediment accumulation rates associated with recent human population growth and land-use changes[END_REF]. Marine ecosystems, in particular, are deteriorating, with degradation driven mainly by coastal development, offshore energy production, fisheries, and pollution [START_REF] Halpern | A global map of human impact on marine ecosystems[END_REF][START_REF] Halpern | Recent pace of change in human impact on the world's ocean[END_REF]. Perhaps it is not surprising, then, that declines in seabird numbers are more pronounced than in most other bird groups [START_REF] Paleczny | Population trend of the world's monitored seabirds, 1950-2010[END_REF], Dias et al. 2019). [START_REF] Rodríguez | Future directions in conservation research on petrels and shearwaters[END_REF] reviewed threats (defined as humaninduced or natural actions or events that negatively affect a species) for shearwaters and petrels (Procellariidae), highlighting that interspecific differences in threats are influenced by numerous behavioural, geographic, and life-history factors. Much attention has focused on population declines and threats to larger seabirds [START_REF] Baker | Albatrosses and petrels in Australia: a review of their conservation and management[END_REF][START_REF] Phillips | The conservation status and priorities for albatrosses and large petrels[END_REF], with fisheries bycatch being a major issue for divers (e.g., alcids and diving duck; [START_REF] Zydelis | The incidental catch of seabirds in gillnet fisheries: a global review[END_REF]) and vessel-attracted scavenging species such as albatrosses [START_REF] Anderson | Global seabird bycatch in longline fisheries[END_REF]. For smaller species, such as storm-petrels, invasive mammals, especially rodents, are raising the most concern [START_REF] Jones | Severity of the effects of invasive rats on seabirds: a global review[END_REF], Bolton et al. 2014, Dias et al. 2019), whereas fisheries bycatch is less of an issue [START_REF] Bugoni | Seabird bycatch in the Brazilian pelagic longline fishery and a review of capture rates in the southwestern Atlantic Ocean[END_REF][START_REF] Jiménez | Structure of the seabird assemblage associated with pelagic longline vessels in the southwestern Atlantic: implications for bycatch[END_REF]; but see [START_REF] Pott | Information gaps limit our understanding of seabird bycatch in global fisheries[END_REF]. Approximately 44% of storm-petrel species are listed on the International Union for Conservation of Nature (IUCN) Red List as Near Threatened, Vulnerable, Endangered, or Critically Endangered, and data are insufficient to determine a threat category for an additional 7% of species (n = 27; BirdLife International 2021; Table A1.S1).

Leach's Storm-Petrel (Hydrobates leucorhous) was recently uplisted from Least Concern to Vulnerable globally (BirdLife International 2018), mainly as a consequence of population declines at northwest Atlantic colonies. The eastern (i.e., Atlantic) Canadian population was designated as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC; COSEWIC 2020), the UK population was moved from Amber to Red by the UK Birds of Conservation Concern 5 [START_REF] Stanbury | The status of our bird populations: the fifth Birds of Conservation Concern in the United Kingdom, Channel Islands, and Isle of Man and second IUCN REdList assessment of extinction risk for Great Britain[END_REF]), and the European population from Near Threatened to Vulnerable in the European Red List of Birds (Birdlife International 2021; [START_REF] Deakin | Decline of Leach's storm petrels Hydrobates leucorhous at the largest colonies in the northeast Atlantic[END_REF]. In general, storm-petrels are difficult to monitor and, therefore, colony abundance and population trends are either estimated infrequently or not available [START_REF] Olivier | Distribution and abundance of Wilson's storm-petrels Oceanites oceanicus at two locations in East Antarctica: testing habitat selection mode[END_REF][START_REF] Insley | Markrecapture and playback surveys reveal a steep decline of European Storm Petrels Hydrobates pelagicus at the largest colony in western Scotland[END_REF]. However, Leach's Storm-Petrel is one of the most studied storm-petrel species, breeding from the Gulf of Maine to southern Labrador in the western North Atlantic, to Iceland, the British Isles, and coastal Norway in the eastern North Atlantic, and from Hokkaido to the Aleutians and Baja California in the Pacific [START_REF] Pollet | Leach's Storm-Petrel (Hydrobates leucorhous), version 1.1[END_REF]. In western North Atlantic colonies, apparent adult survival rates for Leach's Storm-Petrels range from 79%-86% at a number of colonies, which is lower than expected for population stability [START_REF] Fife | Apparent survival of adult Leach's Storm-petrels (Oceanodroma leucorhoa) breeding on Bon Portage Island, Nova Scotia[END_REF], COSEWIC 2020), whereas limited data using a short time series from two Pacific Ocean colonies suggest a higher (94%-99%) apparent survival rate [START_REF] Rennie | High apparent survival of adult Leach's Storm-petrels Oceanodroma leucorhoa in British Colombia[END_REF]. Concomitant with low adult survival rate, population sizes have been decreasing at several large Atlantic colonies [START_REF] Wilhelm | Update and trends of three important seabird populations in the western North Atlantic using a geographic information system approach[END_REF], 2019, Pollet and Shutler 2018, 2019[START_REF] D'entremont | Breeding population decline and associations with nest site use of Leach's Storm-Petrels on Kent Island, New Brunswick from 2001 to 2018[END_REF][START_REF] Deakin | Decline of Leach's storm petrels Hydrobates leucorhous at the largest colonies in the northeast Atlantic[END_REF]. Thus, reduced adult survival in western North Atlantic colonies could be a key driver of population decline.

Following the listing of Leach's Storm-Petrel as Vulnerable by the IUCN and Threatened by COSEWIC, a list of threats was compiled (BirdLife International 2018, COSEWIC 2020). Yet, understanding the impact of threats is complicated by the enormous spatial range of Leach's Storm-Petrels throughout their life cycle. Leach's Storm-Petrels forage hundreds of kilometers from their colony during the breeding season [START_REF] Halpin | Year-round movements of sympatric Fork-tailed (Oceanodroma furcata) and Leach's (O. leucorhoa) storm-petrels[END_REF][START_REF] Hedd | offshore habitat use, and colony overlap by incubating Leach's Storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic[END_REF] and are trans-equatorial migrants during the non-breeding season [START_REF] Halpin | Year-round movements of sympatric Fork-tailed (Oceanodroma furcata) and Leach's (O. leucorhoa) storm-petrels[END_REF], Pollet et al. 2019). Given that this species is globally distributed across a seascape spanning a variety of threats and stressors, conservation planning must also consider spatial and temporal variation in risk. Current knowledge suggests that populations in the Pacific may be faring better than those in the Atlantic, potentially because of a different suite of threats in each ocean. Spatial variation is invaluable for assessing cumulative risk (but see [START_REF] Lieske | Seas of risk": assessing the threats to colonialnesting seabirds in Eastern Canada[END_REF]), but it is often difficult to estimate given that multiple threats can influence ecosystems in a variety of ways. As such, solicitation of expert opinion is an effective approach to synthesize the current state of knowledge regarding sensitivity of marine birds to threats [START_REF] Lieske | Synthesizing expert opinion to assess the at-sea risks to seabirds in the western North Atlantic[END_REF]. In this context, we created a survey with which Leach's Storm-Petrel researchers ranked threats for different colonies to assess spatial variation in risk, with the goal of supporting the selection of appropriate conservation strategies across the global range. We also identified knowledge gaps to be addressed to assist conservation of storm-petrels, and to inform conservation planning processes.

METHODS

The lead author contacted 48 Leach's Storm-Petrel researchers from nine countries or territories (Canada, Faroe Islands, Iceland, Japan, Mexico, Russia, St. Pierre et Miquelon, United Kingdom, and United States) covering the species' global breeding range to complete a survey (Appendix 1). The selected researchers have published articles on Leach's Storm-Petrels and were at different stages of their careers. The survey first asked researchers about their professional affiliations, how long they had been working with the species, and the location of the breeding colony(ies) where they conducted their research. Hence, threats that had caused extirpation of colonies were excluded from this survey. Participants were then asked to rank the importance of seven terrestrial and five at-sea threats (during both the breeding and non-breeding seasons; Table 1) at colony(ies) where they conduct

DATA ANALYSIS

To determine which threat was the most important, weighted ordinal values were determined by the number of threat options in each question, with the top threat given the most weight. A top-ranked terrestrial threat was given a value of seven and a topranked at-sea threat was given a value of five. A lowest-rank terrestrial or at-sea threat was given a value of one. When a survey participant did not rank all proposed threats, we gave top values to the ranked threats and assumed the others were negligible (Table A1.S2). A score for each threat was calculated by summing all weighted values at three different geographic scales, as follows: global, ocean basin sector (western Atlantic, eastern Atlantic, western Pacific, and eastern Pacific), and jurisdiction (state, province, country). The number of participants was unequal among regions (jurisdiction and basin scales); therefore, score values varied greatly among regions. Hence, we determined for each threat what percent of the total weighted score it represented in each region.

RESULTS

Thirty-seven researchers (the authors) responded to the survey, representing eight of the nine countries where Leach's Storm-Petrels breed (we were unable to secure responses from Russia), with two, eight, twenty-four, and five responses for the western and eastern North Pacific, and the western and eastern North Atlantic, respectively. Most participants were government employees (n = 16), followed by university researchers (n = 15), but the group also included non-governmental organization employees (n = 5) and a museum employee (n = 1). More than two-thirds of participants (n = 26) had studied Leach's Storm-Petrels for more than 11 years and their combined experience represented a minimum of 433 years.

Terrestrial threats

Globally, survey participants ranked the three most important terrestrial threats that currently affect existing colonies as avian predators, mammalian predators, and onshore light attraction, with rankings differing among regions (Fig. 1; Table 2). Avian predators were the top threat in all four ocean basin sectors, tied with mammalian predation in the eastern Pacific. At the jurisdiction level, avian predators had the highest or second highest summed weighted scores in all but one case, the Faroe Islands, where they ranked fourth. Mammalian predators were ranked first, second, or third in the eastern Pacific, western Atlantic, and eastern Atlantic, respectively, but were not perceived as a threat in the western Pacific. At the jurisdiction level, mammalian predators ranked among the top three threats in nine of fourteen cases (64%). They were not ranked as a threat in four jurisdictions (Japan, Mexico, St. Pierre et Miquelon, and Iceland). Onshore light attraction received the third highest weight, ranking third in the western Atlantic and eastern Pacific, but only fifth in the western Pacific and eastern Atlantic. At the jurisdiction level, onshore light attraction was ranked second in Newfoundland and Labrador, New Brunswick, California (tied with avian predation), and St. Pierre et Miquelon (tied with avian predation and habitat loss), third in Alaska, British Columbia, and Mexico, and fourth to sixth elsewhere (Fig. 1). There was a high consistency in the responses from the survey participants at the jurisdiction level. This concordance of expert opinion was not present at the basin or global scales (Table A1.S3). The heterogeneity in perceived threats is potentially the result of the combined effect of the different specific issues faced at their colonies and the perceptions of the survey participants.

At-sea threats during breeding season

The top four at-sea threats during the breeding season were offshore light attraction, spatial shifts in prey, mercury, and pesticides and other contaminants (Fig. 2; Table 3). Offshore light attraction ranked first in the east Pacific, spatial shifts in prey ranked first in the east and west Atlantic, mercury ranked second in the west Atlantic and fourth in the eastern Pacific and the eastern Atlantic. Pesticides and other contaminants were either third (east Pacific, east Atlantic) or fourth (west Atlantic; Fig. 2). At the jurisdiction level, spatial shifts in prey items were ranked (2) 20.9 (4) 11.4

(3) 0.9 (1) 0.0 (0) Overall 28.5 18.5 16.5 12.1 9.0 7.9 6.2 1.3 first for seven jurisdictions, offshore light attraction was ranked first for three jurisdictions, and mercury and pesticides and other contaminants each ranked first for one jurisdiction (Fig. 2). Survey participants were in agreement with the most important threats within each jurisdiction but not at the basin or global scale (Table A1.S4).

At-sea threats during non-breeding season

The top four offshore threats during the non-breeding season were the same as during the breeding season, namely offshore light attraction, spatial shifts in prey, mercury contamination, and pesticide contamination (Fig. 3; Table 3). However, the order at the ocean-basin scale was somewhat different. Offshore light attraction ranked first as a threat in the east Pacific and west Atlantic but only seventh in the east Atlantic, where spatial shifts in prey items ranked first (Fig. 3; Table 3). At the jurisdiction level, responses from survey participants were fairly consistent, with spatial shifts in prey items ranked first in five jurisdictions, offshore light attraction ranked first for four jurisdictions, mercury ranked first for one jurisdiction, and pesticides and other contaminants and prey depletion each ranked first for one jurisdiction. The agreement among survey participants was slightly more pronounced at the jurisdiction scale than at the basin scale (Table A1.S5).

GENERAL PERSPECTIVES ON THREATS

Avian predators

Avian predators of Leach's Storm-Petrels include Herring Gulls (Larus argentatus and L. smithsonianus), Great Black-backed Gulls (L. marinus), Lesser Black-backed Gulls (L. fuscus), Slatybacked Gulls (L. schistisagus), Great-horned Owls (Bubo virginianus), Great Skuas (Stercorarius skua), and corvids (Corvidae; [START_REF] Stenhouse | Herring gull Larus argentatus predation on Leach's Storm-petrels Oceanodroma leucorhoa breeding on Great Island, Newfoundland[END_REF][START_REF] Votier | Nocturnal foraging by great skuas Stercorarius skua: implications for conservation of storm-petrel populations[END_REF][START_REF] Veitch | Great black-backed gull (Larus marinus) predation on seabird populations at two colonies in Eastern Canada[END_REF][START_REF] Hey | Gull predation on Leach's Hydrobates leucorhous and European Storm-petrels H. pelagicus on Elliðaey Island, Iceland[END_REF], Pollet and Shutler 2019, Pollet et al. 2021).

Corvids tend to destroy nest-burrows and presumably prey on adults, eggs, and nestlings, whereas gulls, skuas, and owls mostly prey on adults, although it is unclear if this includes breeding or non-breeding birds or both [START_REF] Hoeg | Levels of predation at two Leach's Storm Petrel Hydrobates leucorhous breeding colonies[END_REF]). However, the high proportion of the local Leach's Storm-Petrel population estimated consumed annually at some colonies (e.g., 9% on Great Island, Newfoundland, 16% on St. Kilda, Scotland [START_REF] Stenhouse | Herring gull Larus argentatus predation on Leach's Storm-petrels Oceanodroma leucorhoa breeding on Great Island, Newfoundland[END_REF][START_REF] Votier | Nocturnal foraging by great skuas Stercorarius skua: implications for conservation of storm-petrel populations[END_REF]) is not sustainable if all predation was on breeding adults, suggesting that breeding and non-breeding birds are being preyed on [START_REF] Bicknell | Potential consequences of discard reform for seabird communities[END_REF]. In Newfoundland, capelin (Mallotus villosus) can be a major part of Herring Gull diets, and delayed capelin spawning caused gulls to use alternate food sources, including seabirds [START_REF] Massaro | Delayed capelin (Mallotus villosus) availability influences predatory behaviour of large gulls on black-legged kittiwakes[END_REF], such as storm-petrels [START_REF] Stenhouse | Indirect effects of the availability of capelin and fishery discards: gull predation on breeding storm-petrels[END_REF]. However, at Atlantic colonies, gulls breed earlier than Leach's Storm-Petrels.

When juvenile storm-petrels leave their burrows, gulls are not attending colonies, which presumably reduces this direct predation pressure on fledging individuals [START_REF] Hoeg | Levels of predation at two Leach's Storm Petrel Hydrobates leucorhous breeding colonies[END_REF]). However, there is considerable predation of fledglings by gulls during onshore wrecks and at illuminated coastal facilities [START_REF] Burt | Influence of anthropogenic light on the attraction and mortality of Leach's Storm-Petrels. Where, when, why and which birds[END_REF].

In eastern Canada, Herring Gull and Great Black-backed Gull populations decreased following the collapse of the northern cod fishery that provided gulls with a large food source from offal [START_REF] Regular | Canadian fishery closures provide a largescale test of gillnet bycatch on seabird populations[END_REF], Wilhelm et al. 2016[START_REF] Weseloh | Herring gull (Larus argentatus), version 1.0[END_REF]. We might therefore expect avian predation on storm-petrels to decrease, although some individual gulls specialize in feeding on storm-petrels [START_REF] Pierotti | Diet choice in the herring gull: constraints imposed by reproductive and ecological factors[END_REF]Annett 1991, Hey et al. 2019). In skuas, specializing on seabirds and/or prey-switching from discards to seabirds (including storm-petrels) results in high levels of stormpetrel predation [START_REF] Votier | Nocturnal foraging by great skuas Stercorarius skua: implications for conservation of storm-petrel populations[END_REF]. Changes in regional fisheries policy could also affect those behaviors in the future [START_REF] Votier | Changes in fisheries discard rates and seabird communities[END_REF][START_REF] Bicknell | Potential consequences of discard reform for seabird communities[END_REF].

Avian predation pressure may also be influenced by small mammal population dynamics on islands, where avian predators are initially attracted by the mammals but switch to seabirds once the nesting season begins. In cases where conservation strategies include removal of problematic mammals (e.g., mice, voles, and hares), there is potential for unintended consequences of predator diet-switching that inadvertently increases predation pressure on storm-petrels [START_REF] Rayner | Spatial heterogeneity of mesopredator release within an oceanic island system[END_REF][START_REF] Hervías | Studying the effects of multiple invasive mammals on Cory's shearwater nest survival[END_REF]. Dynamics among avian predators and predation on storm-petrels and other prey may be complex and differ among regions and colonies [START_REF] Stenhouse | Indirect effects of the availability of capelin and fishery discards: gull predation on breeding storm-petrels[END_REF][START_REF] Steenweg | Seasonal and age-dependent dietary partitioning between the great black-backed and herring gulls[END_REF][START_REF] Thomsen | El Niño/Southern Oscillation-driven rainfall pulse amplifies predation by owls on seabirds via apparent competition with mice[END_REF]. In some cases, removal of just a few specialist avian predators has some positive effect on prey species (Sanz-Aguilar et al. 2009, Scopel and[START_REF] Scopel | Predation and foodweather interactions drive colony collapse in a managed metapopulation of Arctic terns (Sterna paradisaea)[END_REF]. Where human activities have exacerbated avian predation, management strategies should be carefully considered. These strategies must also have clear objectives for both predator and prey, with an evaluation plan to assess if targets are met and the implementation of adaptive management when objectives are not reached [START_REF] Libois | Nest boxes: a successful management tool for the conservation of an endangered seabird[END_REF][START_REF] Fuentes | Adaptive management of marine mega-fauna in a changing climate[END_REF][START_REF] Bourgeois | Are artificial burrows efficient conservation tools for seabirds? A case study of two sympatric shearwaters on neighbouring islands and guidelines for improvement[END_REF]. In other cases of avian predation from a native predator, management might not be advisable. Avian species may also be competitors, with examples of Atlantic Puffins (Fratercula arctica) outcompeting Leach's Storm-Petrel for nesting sites [START_REF] Lormee | Population survey of Leach's Storm-petrels breeding at Grand Colombier Island, Saint-Pierre and Miquelon Archipelago[END_REF][START_REF] Wilhelm | Update and trends of three important seabird populations in the western North Atlantic using a geographic information system approach[END_REF], 2019).

Mammalian predators

Seabirds tend to breed on islands free of mammalian predators and, as a result, may lack anti-predator defense mechanisms (e.g., [START_REF] Buxton | Deciding when to lend a helping hand: a decisionmaking framework for seabird island restoration[END_REF]. Therefore, seabirds are highly vulnerable if mammalian predators are introduced to a colony [START_REF] Borrelle | Influence on recovery of seabirds on islands where invasive predators have been eradicated, with a focus on Procellariiformes[END_REF], and they rarely coexist with introduced mammalian predators (De León et al. 2006). Historical presence of introduced mammalian predators (mostly rats) has decimated storm-petrel colonies [START_REF] Mcclelland | Breeding biology of Tristram's storm-petrels Oceanodroma tristrami at French Frigate Shoals and Laysan Island, Northwest Hawaiian Islands[END_REF], making mammalian predators the top threat for storm-petrels [START_REF] Dias | Threats to seabirds: a global assessment[END_REF]. Mammalian predators can also naturally occur on seabird islands, and measures to deal with naturally occurring mammals will be different than for introduced species. Co-occurrences of mammalian predators with storm-petrels will have different outcomes depending on the density of other species, and it is not necessarily a sustainable situation [START_REF] Towns | Have the harmful effects of introduced rats on islands been exaggerated?[END_REF]; but see various periods of time and are potential predators of eggs, nestlings, and/or adults (Skelpkovych and [START_REF] Sklepkovych | Food availability and food hoarding behaviour by Red and Arctic foxes[END_REF][START_REF] Bicknell | Probable predation of Leach's Storm-Petrel Oceanodroma leucorhoa eggs by St Kilda field mice Apodemus sylvaticus hirtensis[END_REF], 2020[START_REF] Hoeg | Levels of predation at two Leach's Storm Petrel Hydrobates leucorhous breeding colonies[END_REF]. For example, over 900 Leach's Storm-Petrels were found in larders of red foxes over six years on Baccalieu Island, Newfoundland and Labrador, Canada, the species' largest colony, which is now free of these predators [START_REF] Sklepkovych | Food availability and food hoarding behaviour by Red and Arctic foxes[END_REF]. Red foxes have recently been detected in some colonies in Quebec (J.-F. Rail, personal observation). In British Columbia, North American river otters (Lontra canadensis) have been implicated in declines of Leach's Storm-Petrels [START_REF] Carter | Historical colony status and recent extirpations of burrow-nesting seabirds at Seabird Rocks, British Columbia[END_REF]. In one breeding season, an American mink and North American river otter killed at least 700 adult Leach's Storm-Petrels at Country Island Nova Scotia, Canada (J. Rock, personal communication). Nova Scotia has the largest mink farming industry in Canada [START_REF] Bowman | Hybridization of domestic mink with wild American mink (Neovison vison) in eastern Canada[END_REF].

Mink are powerful swimmers, and a single mink, wild or escaped, arriving in a seabird colony can have devastating impacts because they engage in surplus killing [START_REF] Roesler | A new threat for the globally endangered hooded grebe Podiceps gallardoi: the American mink Neovison vison[END_REF]. In contrast, introduced predators usually occur because of some accidental or deliberate anthropogenic intervention and may have greater impacts on seabird colonies. Introduced mammalian predators are a major global problem at seabird colonies [START_REF] Dias | Threats to seabirds: a global assessment[END_REF], and both prevention and early detection of introduced predators should be of high priority because costs associated with

Mammalian herbivores

The presence of mammalian herbivores is often the result of deliberate introduction by humans. Mammalian herbivores are a threat to Leach's Storm-Petrels through soil erosion and compaction, burrow destruction, and changes in vegetation composition and structure [START_REF] Peterson | Tree recruitment limitation by introduced snowshoe hares, Lepus americanus, on Kent Island, New Brunswick[END_REF]. For example, in the western North Atlantic, the most commonly introduced species are snowshoe hares (Lepus americanus), historically introduced as food for island caretakers or as sources of pelts [START_REF] Wheelwright | Eradication of an ecosystem engineer[END_REF], and sheep (Ovis spp.), introduced for seasonal or year-round pasturing. White-tailed deer (Odocoileus virginianus) are not introduced in Nova Scotia but often swim to breeding colonies (I. Pollet, personal observation). Although they are herbivores, sheep and deer regularly consume eggs of groundnesting birds and have been documented occasionally biting off legs, wings, or heads of young seabirds [START_REF] Furness | Predation on ground-nesting seabirds by island populations of red deer Cervus elaphus and sheep Ovis[END_REF]). However, the presence of mammalian herbivores is a far lower mortality risk to storm-petrels than is the presence of mammalian predators.

Onshore light attraction and collisions

Leach's Storm-Petrels travel to and from their colonies at night, presumably to avoid diurnal predators, especially gulls [START_REF] Watanuki | Moonlight avoidance behavior in Leach's Storm-petrels as a defense against Slaty-backed Gulls[END_REF], Pollet et al. 2021). They likely use moonlight to visualize landscape cues, but it is not their only cue [START_REF] Yoda | Compass orientation drives naïve pelagic seabirds to cross mountain ranges[END_REF][START_REF] Wynn | Natal imprinting to the Earth's magnetic field in a pelagic seabird[END_REF]. Juveniles are especially attracted to light (Wilhelm et al. 2021[START_REF] Burt | Influence of anthropogenic light on the attraction and mortality of Leach's Storm-Petrels. Where, when, why and which birds[END_REF]) and, when onshore, birds are susceptible to collisions with buildings and vehicles, more prone to predation, and can become disoriented and grounded [START_REF] Troy | Using observed seabird fallout records to infer patterns of attraction to artificial light[END_REF][START_REF] Rodríguez | Artificial lights and seabirds: is light pollution a threat for the threatened Balearic petrels?[END_REF]. Effects of this threat depend on the proximity of a colony to onshore light sources and the type, color, and direction of lights [START_REF] Miles | Effects of artificial lights and moonlight on petrels at St Kilda[END_REF][START_REF] Rodríguez | Reducing lightinduced mortality of seabirds: high pressure sodium lights decrease the fatal attraction of shearwaters[END_REF], Syposz et al. 2021). More than 1900 stranded Leach's Storm-Petrels were found on the island of Newfoundland during autumn 2018 and 2019 [START_REF] Wilhelm | Effects of land-based light pollution on two species of burrow-nesting seabirds in Newfoundland and Labrador, Canada[END_REF], but these onshore stranding events have not been monitored systematically (but see Burt 2022); therefore, the total impact of onshore strandings is not well known. From a conservation perspective, onshore light attraction is probably one of the easiest threats to mitigate and reduce. For example, people living on island communities are invited to turn off their lights during peak fledgling seasons of endemic seabirds (https://web.archive.org/web/20221019115210/https://www.lesjoursdelanuit. re/; https://web.archive.org/web/20221019115223/https://birdlifemalta. org/wp-content/uploads/2020/07/Guidelines-for-Ecologically-Responsible-Lighting.pdf), and Kaua'i (Hawai'i, USA) residents are encouraged to place stranded shearwaters in "Shearwater Aid Stations" for care and safe release [START_REF] Telfer | Attraction of Hawaiian seabirds to lights: conservation efforts and effects of moon phase[END_REF]. Such measures could complement information campaigns to reduce stranding events and rescue stranded birds [START_REF] Ainley | The status and population trends of the Newell's shearwater on Kaua'i: insights from modeling[END_REF][START_REF] Le Corre | Rescue of the Mascarene Petrel, a critically endangered seabird of Réunion Island, Indian Ocean[END_REF], Wilhelm et al. 2021).

Disturbance

Recreational disturbance was considered a threat, and some survey respondents added researcher disturbance to the threat list. Effects of disturbance can be difficult to quantify. Nonetheless, visitors and people handling birds at colonies of burrow-nesting seabirds can negatively affect fledgling body mass, cause nestling mortality, or provoke nest abandonment by incubating or provisioning adults [START_REF] Blackmer | Effects of investigator disturbance on hatching success and nest-site fidelity in a long-lived sea bird, Leach's storm-petrel[END_REF][START_REF] Albores-Barajas | Are burrow nesting seabird chicks affected by human disturbance?[END_REF][START_REF] Watson | Out of sight but not out of harm's way: human disturbance reduces reproductive success of a cavity-nesting seabird[END_REF]. Active burrows can collapse from trampling. Some seabird colonies are difficult to access, which limits human disturbance, but some colonies, such as in the Faroe Islands, are situated near human settlements and experience seasonal influxes of tourists (A. Ausems, personal observation). Using paleo-ecological records, [START_REF] Duda | Linking 19th century European settlement to the disruption of a seabird's natural population dynamics[END_REF] documented a severe decline in a North American colony once European settlers arrived in the area in the early 1800s, and the colony has yet to fully recover.

Recently, unmanned aerial vehicles (drones) have been used to limit disturbance from researchers surveying surface-nesting birds and even burrow-nesting birds when vegetation cover is minimal (Borrelle andFletcher 2017, Albores-Barajas et al. 2018). Breeding status of burrow-nesting birds can be assessed with burrow-scopes (i.e., endoscopic cameras), but human presence is still required within colonies to operate them [START_REF] Surman | A survey of the breeding seabirds and migratory shorebirds of the Houtman Abrolhos, Western Australia[END_REF]. Researchers are attempting to reduce disturbance (trampling, repeated grubbing) in study plots where long-term monitoring of population demography occurs by developing remote methods such as Passive Integrated Transponders (PIT) tag burrow-monitoring technology [START_REF] Zangmeister | Incubation failure and nest abandonment by Leach's Storm-petrels detected using PIT tags and temperature loggers[END_REF]D. Fifield, personal communication) and acoustic monitoring [START_REF] Orben | Comparing imaging, acoustics, and radar to monitor Leach's storm-petrel colonies[END_REF].

Offshore light attraction and collisions

Lights at offshore oil and gas platforms are responsible for seabird strandings or collisions at structures or incineration from contact with flames [START_REF] Wiese | Seabirds at risk around offshore oil platforms in the North-west Atlantic[END_REF][START_REF] Montevecchi | Influences of artificial light on marine birds[END_REF], Ronconi et al. 2015;[START_REF] Davis | Study of seabird attraction to the Hebron Production Platform: a proposed study approach[END_REF]. In Nova Scotia and Newfoundland and Labrador, Canada, offshore structures occur within the foraging ranges of major Leach's Storm-Petrel colonies [START_REF] Hedd | offshore habitat use, and colony overlap by incubating Leach's Storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic[END_REF], and Leach's Storm-Petrels are by far the most numerous species reported stranded, with 6920 individuals reported between 1998 and 2018 (87% of all reported birds), which undoubtedly is an underestimate of the total numbers stranded [START_REF] Gjerdrum | Bird strandings and bright lights at coastal and offshore industrial sites in Atlantic Canada[END_REF]). Leach's Storm-Petrels breeding at Gull Island, Newfoundland and Labrador, flew within the light catch-basin of an oil platform in 17.5% of trips, although they tended to transit rapidly past platforms during the day (when light attraction may be minimal), whereas exposure to oil platforms at night occurred in only 1.1% of trips but represents a very large number of individual trips considering the number trips each bird takes during a season [START_REF] Collins | Foraging paths of breeding Leach's Stormpetrels in relation to offshore oil platforms, breeding stage, and year[END_REF]).

Lighting at offshore operations is important for worker safety and for maritime and air navigation, so mitigation strategies must not increase human risks. In Canadian offshore industries, 76% of stranded storm-petrels are found alive [START_REF] Gjerdrum | Bird strandings and bright lights at coastal and offshore industrial sites in Atlantic Canada[END_REF], presenting opportunities for mitigation through search and release. In addition to offshore oil and gas platforms, offshore lights can also originate from emerging offshore wind facilities, vessels in transit or working offshore, as well as cruise and cargo ships. Squid-fishing fleets in particular use powerful lights to attract squid to the surface [START_REF] Waluda | Quantifying light-fishing for Dosidicus gigas in the eastern Pacific using satellite remote sensing[END_REF], and the location and timing of squid-fishing season can coincide with either the breeding or the migration of storm-petrels [START_REF] Mciver | Use of social attraction to restore Ashy Storm-Petrels Oceanodroma homochroa at Orizaba Rock, Santa Cruz Island, California[END_REF]. The extent and magnitude of strandings on vessels is largely unknown with respect to potential population-level impacts.

Spatial shifts in prey and climate change

Spatial shifts in seabird prey can be an indirect consequence of climate change. Changing environmental conditions, such as rising sea surface temperature, can induce a spatial shift of marine species because they gravitate to their preferred thermal preferences (Grémillet andBoulinier 2009, Kleisner et al. 2016). During marine heat waves, some Leach's Storm-Petrels can temporarily shift their feeding habits and forage on or near shore [START_REF] D'entremont | On-land foraging by Leach's Storm-petrels Oceanodroma leucorhoa coincides with anomalous weather conditions[END_REF]. During breeding seasons, seabirds in general are central place foragers and thus limited in their foraging range by the necessity to return to their colony [START_REF] Elliott | Central-place foraging in an Arctic seabird provides evidence for Storer-Ashmole's halo[END_REF]). The foraging range of Leach's Storm-Petrels is 400-800 km depending on the colony [START_REF] Hedd | offshore habitat use, and colony overlap by incubating Leach's Storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic[END_REF][START_REF] Mauck | Female and male Leach's Storm Petrel (Hydrobates leucorhous) pursue different foraging strategies during the incubation period[END_REF], which is a great distance considering they only weigh ~45g. If preferred prey species shift outside of maximum viable foraging range, seabirds must switch to alternative prey species that might not provide sufficient nutrition or extend their foraging trips, with the associated energy expenditure potentially leading to breeding failure [START_REF] Ponchon | When things go wrong: inter-season dynamics of breeding failure in a seabird[END_REF][START_REF] Fayet | Local prey shortages drive foraging costs and breeding success in a declining seabird, the Atlantic puffin[END_REF]. Some dietary shifts in Leach's Storm-Petrels have been observed at various timescales [START_REF] Hedd | Diets and distributions of Leach's storm-petrel (Oceanodroma leucorhoa) before and after an ecosystem shift in the northwest Atlantic[END_REF][START_REF] Fairhurst | Feather-based measures of stable-isotopes and corticosterone reveal a relationship between trophic position and physiology in a pelagic seabird over a 153-year period[END_REF]. Ecological impacts of these dietary shifts are not clear, though they may be related to decreases in breeding success [START_REF] Mauck | Annual global mean temperature explains reproductive success in a marine vertebrate from 1955 to 2010[END_REF]. Some survey participants included prey depletion and climate change as additional threats, and it is difficult to differentiate spatial shifts in prey from prey depletion. Extreme weather events were not provided as a threat category in the survey but were added by several participants. Severe storms during the breeding season may flood burrows and drown or chill chicks. Moreover, the start of fall migration and the fledging of storm-petrel chicks coincides with the peak of the hurricane season in the Atlantic, and hurricanes and onshore winds may force storm-petrels onshore [START_REF] Boyd | The "wreck" of Leach's petrels in the autumn of 1952[END_REF][START_REF] Teixeira | The wreck of Leach's Storm-petrels on the Portuguese coast in the autumn of 1983[END_REF], Wilhelm et al. 2021).

Mercury

Mercury is a globally distributed, toxic metal that, at sufficient concentrations, can have negative effects on neuroendocrine systems, lead to reduced reproductive success, and induce motor and behavioral problems [START_REF] Wolfe | Effects of mercury on wildlife: a comprehensive review[END_REF][START_REF] Scheuhammer | Recent progress on our understanding of the biological effects of mercury in fish and wildlife in the Canadian Arctic[END_REF][START_REF] Evers | The effects of methylmercury on wildlife: a comprehensive review and approach for interpretation[END_REF]. In aquatic environments, mercury is transformed by bacteria into methylmercury [START_REF] Lehnherr | Methylmercury biochemistry: a review with special reference to Arctic aquatic ecosystems[END_REF]. Methylmercury biomagnifies in food webs, and, during periods of stress or poor body condition, may be released from tissue reserves at concentrations that create physiological, physical, or behavioural problems [START_REF] Fort | Mercury in wintering seabirds, an aggravating factor to winter wrecks?[END_REF]. Storm-petrels, and Procellariiformes in general, have some of the highest tissue mercury levels among seabirds [START_REF] Carravieri | Mercury exposure in a large subantarctic avian community[END_REF][START_REF] Becker | Feather mercury concentrations in Southern Ocean seabirds: variation by species, site and time[END_REF]. Mercury exposure also varies spatially, and in the Gulf of Maine, Leach's Storm-Petrels have high mercury concentrations compared to other sympatric seabirds [START_REF] Goodale | Maine foraging birds as bioindicators of mercury in the Gulf of Maine[END_REF][START_REF] Bond | Mercury concentrations in seabird tissues from Machias Seal Island, New Brunswick, Canada[END_REF]. Mercury exposure in the western North Atlantic, particularly in deep offshore waters, appears to be high for some species, including Leach's Storm-Petrels [START_REF] Goodale | Maine foraging birds as bioindicators of mercury in the Gulf of Maine[END_REF], Mallory et al. 2018;N. Burgess et al. 2019, personal communication) and Little Auks (Alle alle), another planktivore [START_REF] Fort | Spatial ecotoxicology: migratory Arctic seabirds are exposed to mercury contamination while overwintering in the northwest Atlantic[END_REF]. Mercury has been considered a potential problem for Leach's Storm-Petrels for decades [START_REF] Pearce | Shell thinning and residues of organochlorines and mercury in seabirds' eggs, Eastern Canada, 1970-76[END_REF][START_REF] Elliott | Heavy metals and metallothionein concentrations in Atlantic Canadian seabirds[END_REF]), but to date there is little evidence of deleterious effects (Pollet et al. 2017, submitted;[START_REF] Krug | Marine pollution in fledged Leach's storm-petrels (Hydrobates leucorhous) from Baccalieu Island, Newfoundland and Labrador, Canada[END_REF].

In recent years, reductions of mercury emissions in some regions (North America and the European Union) and industrial sectors (e.g., energy production) have been encouraging yet, in 2015, global emissions were still 20% higher than in 2010 (UN Environment Programme 2019). Increasing mercury emissions and legacy mercury already in soil, sediments, and aquatic systems will continue to produce methylmercury for millennia; therefore, monitoring concentrations in biota should continue.

Pesticides and other contaminants

This broad category could include hydrocarbons, trace elements, hydrophobic persistent organic pollutants, and plastics. Most of these substances are poorly studied in Leach's Storm-Petrels, but, in Atlantic Canada, [START_REF] Elliott | Heavy metals and metallothionein concentrations in Atlantic Canadian seabirds[END_REF] found high levels of selenium and cadmium in Leach's Storm-Petrels relative to other sympatric seabirds. However, the high levels of metallothionein that Leach's Storm-Petrels produce endogenously may enable them to limit effects of high tissue concentrations of heavy metals [START_REF] Osborn | A naturally occurring cadmium and zinc binding protein from the liver and kidney of Fulmarus glacialis, a pelagic North Atlantic seabird[END_REF][START_REF] Elliott | Heavy metals and metallothionein concentrations in Atlantic Canadian seabirds[END_REF]. Organic compounds and organochlorines also vary spatially in concentration [START_REF] Megson | Identifying the provenance of Leach's storm petrels in the North Atlantic using polychlorinated signatures derived from comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry[END_REF]) and were at low concentrations in eggs of Fork-tailed Storm-Petrels (Hydrobates furcata) and Leach's Storm-Petrels in Alaska, with PCB concentrations below toxicity thresholds (D. D. Rudis and B. L. Slater 2009, personal communication). None of these contaminant studies evaluated toxicological effects of measured concentrations.

Like many seabird species, Leach's Storm-Petrels ingest plastic [START_REF] Bond | Effectiveness of emetics to study ingestion by Leach's Storm-Petrels (Oceanodroma leucorhoa)[END_REF]. [START_REF] Krug | Marine pollution in fledged Leach's storm-petrels (Hydrobates leucorhous) from Baccalieu Island, Newfoundland and Labrador, Canada[END_REF] found high frequencies of occurrence (87.5%) of plastic debris in recently fledged stormpetrels in Atlantic Canada, and when using emetics (which recover all plastic in the gastrointestinal tract), 48% of adults sampled at Gull Island, Newfoundland and Labrador had also ingested plastic [START_REF] Bond | Effectiveness of emetics to study ingestion by Leach's Storm-Petrels (Oceanodroma leucorhoa)[END_REF]). Leach's Storm-Petrels spend most of their time at sea in contact with the ocean surface, either to feed or rest. This makes them vulnerable to hydrocarbons discharged from vessels or offshore platforms and to more voluminous oil spills [START_REF] Fraser | Produced water from offshore oil and gas installations on the Grand Banks, Newfoundland and Labrador: are the potential effects of seabirds sufficiently known?[END_REF][START_REF] Wilhelm | Comparing an estimate of seabirds at risk to a mortality estimate from the November 2004 Terra Nova FPSO oil spill[END_REF][START_REF] Ellis | Mortality of migratory birds from marine commercial fisheries and offshore[END_REF][START_REF] Morandin | Offshore oil and gas, and operational sheen occurrence:Is there potential harm to marine birds?[END_REF].

Bycatch

The unintentional killing of seabirds in fishing gear (seabird bycatch), causes significant global mortality for medium-large tubenose species (such as albatrosses and shearwaters) and divers (e.g., alcids and diving ducks), killing hundreds of thousands of individuals per year [START_REF] Anderson | Global seabird bycatch in longline fisheries[END_REF][START_REF] Croxall | Seabird conservation status, threats and priority actions: a global assessment[END_REF][START_REF] Zydelis | The incidental catch of seabirds in gillnet fisheries: a global review[END_REF], Montevecchi 2022), though bycatch appears rare for Leach's Storm-Petrels [START_REF] Hedd | Characterization of seabird bycatch in eastern Canadian waters, 1998-2011, assessed from onboard fisheries observer data[END_REF][START_REF] Jannot | Seabird bycatch in U.S. West Coast fisheries[END_REF]. Presumably this is related to their foraging mode and dietary preferences and a lack of strong attraction to vessels, fishing bait, or prey in nets.

KNOWLEDGE GAPS AND PRIORITIES FOR FUTURE RESEARCH

Survey participants agreed that predation and light attraction represent major population threats to Leach's Storm-Petrels across their breeding range, with perhaps less importance in the eastern North Atlantic. With relatively easy access to colonies by researchers or predators (compared to following birds at sea), documenting predation seems an obvious and useful task, and carcasses collected at colonies can provide clear evidence (Pollet andShutler 2019, Hoeg et al. 2021). Because storm-petrels spend approximately 90% of their life at sea [START_REF] Pollet | Leach's Storm-Petrel (Hydrobates leucorhous), version 1.1[END_REF], there is significant impetus for quantifying impacts of threats away from colonies. Offshore light attraction appears to be an important threat, but the combined ranking of climate change effects (the spatial shift and depletion in prey items and the weather events) would rank higher than light attraction in many jurisdictions. Low apparent adult annual survival and population declines at several colonies sharing the same wintering areas suggest that threats during the non-breeding season are highly important and are areas of active investigation. Some participants were unable to identify at-sea threats, but that does not mean threats are not present, and, in the Pacific, more research is required to evaluate the population status and to identify threats faced by Leach's Storm-Petrels (Figs. 1 and2). Threats at sea are more difficult to observe, and the effects of some threats may not be independent of other threats (e.g., [START_REF] Tartu | To breed or not to breed: endocrine response to mercury contamination by an Arctic seabird[END_REF]. Increasingly, however, development of miniature tracking technology is enabling researchers to study at-sea distribution and foraging ranges (Pollet et al. 2014a, 2014b, 2019[START_REF] Hedd | offshore habitat use, and colony overlap by incubating Leach's Storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic[END_REF] and to begin identifying threats to storm-petrels in pelagic environments [START_REF] Collins | Foraging paths of breeding Leach's Stormpetrels in relation to offshore oil platforms, breeding stage, and year[END_REF]. Studying Leach's Storm-Petrels during the non-breeding season would involve international collaboration because of the widespread distribution of the species during that time [START_REF] Halpin | Year-round movements of sympatric Fork-tailed (Oceanodroma furcata) and Leach's (O. leucorhoa) storm-petrels[END_REF], Pollet et al. 2019).

Differences in perceived threats in different jurisdictions and the agreement of survey participants within each jurisdiction but not within each basin (Tables A1.S3, A1.S4, and A1.S5) highlight the need to carefully tailor conservation measures in a contextdependent way. Terrestrial threats are probably colony-specific, and conservation measures implemented at a global scale might have different results depending on the colony.

In the western North Atlantic, tracking studies show little overlap in foraging areas for Leach's Storm-Petrels breeding at adjacent colonies [START_REF] Hedd | offshore habitat use, and colony overlap by incubating Leach's Storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic[END_REF], so threats encountered at sea during the breeding season by birds from one colony might differ from those of a neighboring colony. The spatial distribution of risk varies in the seascape, and compared to other seabird species in eastern Canada, Leach's Storm-Petrels have high cumulative risks from threats, which include marine traffic, light pollution, and ship-source oil pollution [START_REF] Lieske | Seas of risk": assessing the threats to colonialnesting seabirds in Eastern Canada[END_REF]. During migration, birds from different colonies within the same ocean basin may follow similar routes, thereby being exposed to the same threats during this portion of their annual cycle (Pollet et al. 2019). Similarly, the degree of migratory connectivity in over-wintering areas may provide common, or divergent, exposure to risk at both the individual and colony levels (González-Solís et al. 2007[START_REF] Frederiksen | Multicolony tracking reveals the winter distribution of a pelagic seabird on an ocean basin scale[END_REF][START_REF] Wheelwright | Eradication of an ecosystem engineer[END_REF].

Seabirds have a diverse range of foraging strategies, body sizes, and diets. Thus, threats will affect each species or guild differently. For example, [START_REF] Lieske | Synthesizing expert opinion to assess the at-sea risks to seabirds in the western North Atlantic[END_REF] concluded that Leach's Storm-Petrels had the highest species-specific risk score for sensitivity to light pollution in the western North Atlantic (i.e., most sensitive of all seabird species in the study). In contrast, in the same study, Leach's Storm-Petrels were ranked least sensitive to fisheries bycatch. Survey participants in the present study ranked offshore lights as the top offshore threat (Table 3). In our study, each threat was considered separately, but, of course, threats are not mutually exclusive and can have additive, synergistic, or antagonistic effects [START_REF] Crain | Interactive and cumulative effects of multiple human stressors in marine systems[END_REF][START_REF] Piggott | Reconceptualizing synergism and antagonism among multiple stressors[END_REF], Dias et al. 2019[START_REF] Lieske | Seas of risk": assessing the threats to colonialnesting seabirds in Eastern Canada[END_REF]. For example, in a given breeding colony, Leach's Storm-Petrels could suffer from both predation and difficulties finding enough prey to feed their chicks.

The current assessment of spatial variation in threats affecting Leach's Storm-Petrels could be applied to some other stormpetrel species living sympatrically because they share many lifehistory traits. This includes European Storm-Petrels (Hydrobates pelagicus) in the eastern North Atlantic and Fork-tailed Storm-Petrels, Ashy Storm-Petrel (H. homochroa), and Least (H. microsoma) and Black Storm-Petrels (H. melania) in the Pacific [START_REF] Carter | Breeding of the Leach's Storm-Petrel Oceanodroma leucorhoa at Santa Catalina Island, California[END_REF][START_REF] Halpin | Year-round movements of sympatric Fork-tailed (Oceanodroma furcata) and Leach's (O. leucorhoa) storm-petrels[END_REF][START_REF] Ausems | Birds of a feather moult together: differences in moulting distribution of four species of storm-petrels[END_REF][START_REF] Bedolla-Guzmán | Year-round niche segregation of three sympatric Hydrobates storm-petrels from Baja California Peninsula, Mexico, Eastern Pacific[END_REF]. In cases where a conservation planning framework is developed to implement and monitor conservation initiatives, spatial variation in threats should be considered to direct conservation actions and biosecurity measures that are most relevant to a particular colony or population [START_REF] Russell | Testing island biosecurity systems for invasive rats[END_REF]. In this way, cumulative threats can be mitigated on a caseby-case basis, contributing to an overall conservation strategy of cumulative actions that maximize positive benefits to the global Leach's Storm-Petrel population.

Fig. 1 .

 1 Fig. 1. Ranks of onshore threats for Leach's Storm-Petrel (Hydrobates leucorhous) evaluated for extant colonies studied by the authors. Threats are presented for each ocean basin sector (top) and state/province/country (bottom). Note that threats that may have led to the extirpation of colonies are not factored into the ranking.

Fig. 2 .

 2 Fig. 2. Ranks of at-sea threats during the breeding season for Leach's Storm-Petrel (Hydrobates leucorhous) evaluated for extant colonies studied by the authors. Threats are presented for each ocean basin sector (top) and state/province/country (bottom).

Fig. 3 .

 3 Fig. 3. Ranks of at-sea threats during the non-breeding season for Leach's Storm-Petrel (Hydrobates leucorhous) evaluated for extant colonies studied by the authors. Threats are presented for each ocean basin sector (top) and state/province/country (bottom).

  , MLM Data curation: ILP Formal Analysis: ILP Methodology: ILP, MLM Visualization: ILP, AKL Writing -original draft: ILP, MLM, ALB, LAMT, RAR Writing -review and editing: ILP, ANMA, CB, YBG, AMJB, MB, ALB, KD, AWD, DAF, CG, LRH, ESH, AH, RH, AKL, HLM, RAM, GTWM, LAMT, WAM, MP, IP, JFR, GJR, JR, RAR, DS, IJS, AT, YW, LJW, SIW, SNPW, MLM

Table 1 .

 1 Terrestrial and at-sea threats to Leach's Storm-Petrel (Hydrobates leucorhous) at existing study colonies given in the survey and added by participants. At-sea threats were presented separately for the breeding and non-breeding season.

		Already in the survey	Added by participants
	Terrestrial threats	Mammalian predators	Researcher disturbance
		Mammalian herbivores	Avian competition for burrow
		Avian predators	Reduction in canopy
		Habitat loss
		Onshore light attraction and collisions
		Recreational disturbance
		Coastal development
	At-sea threats	Mercury poisoning	Climate change
		Contaminant poisoning (other than mercury)	Weather events
		Offshore light attraction and collisions	Predation at offshore platforms
		Bycatch	Prey depletion
		Spatial shift in prey items
	research or have in-depth knowledge. The threats were chosen
	based on the COSEWIC assessment and status report
	(COSEWIC 2020). For each ranking question, survey
	participants could propose additional threats not provided in the
	survey, and researchers were not required to rank all threats. It
	was assumed that, although most research on Leach's Storm-
	Petrels is colony-based, researchers could also evaluate at-sea
	threats.

Table 2 .

 2 Weighted percent threat scores for each terrestrial threat for Leach's Storm-Petrel (Hydrobates leucorhous) at existing study colonies during the breeding season (number of survey participants who ranked each threat). Light: attraction to onshore lights. Threat with the highest score for each ocean basin is bolded.

		Avian	Mammalian	Light	Habitat	Mammalian	Disturbance	Coastal	Unknown
		predators	predator				loss	herbivore			development
	West Pacific	33.3	(2)	0.0	(0)	13.9	(1)	16.7	(1)	0.0	(0)	0.0	(0)	16.7	(1)	19.4	(1)
	East Pacific	28.3	(8)	28.3	(7)	21.4	(6)	4.1	(1)	1.4	(1)	11.1	(4)	2.7	(1)	2.7	(1)
	West Atlantic	27.9 (23)	17.0 (19)	16.8 (17)	14.6 (14)	9.3 (11)	6.9 (12)	7.5	(9)	0.0	(0)
	East Atlantic	30.5	(5)	19.1	(4)	8.6	(3)	8.6

Table 3 .

 3 Weighted percent threat scores for each at-sea threat for Leach's Storm-Petrel (Hydrobates leucorhous) during the breeding and non-breeding season (number of survey participants who ranked each threat). Light: attraction to offshore lights. Threat with the highest score for each ocean basin is bolded.

		Light	Spatial shift in prey	Mercury Pesticides and contaminants	Bycatch	Prey depletion †	Weather events †	Unknown
	At-sea threats during the breeding season
	West Pacific	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	100.0	(2)
	East Pacific	37.8	(8)	20.7	(4)	9.8	(3)	17.1	(5)	8.5	(3)	0.0	(0)	0.0	(0)	6.1	(2)
	West Atlantic	23.6 (19)	26.8 (18)	24.6 (18)	17.6 (17)	2.8	(8)	4.6	(3)	0.0	(0)	0.0	(0)
	East Atlantic	6.9	(1)	34.5	(2)	10.3	(1)	13.8	(1)	0.0	(0)	0.0	(0)	17.2	(1)	17.2	(1)
	Overall	24.7 (28)	25.4 (24)	20.0 (22)	16.8 (23)	3.7 (11)	3.2	(3)	1.2	(1)	5.0	(4)
	At-sea threats during the non-breeding season
	West Pacific	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	0.0	(0)	100.0	(2)
	East Pacific	35.6	(7)	23.7	(4)	10.5	(3)	10.5	(3)	9.2	(3)	0.0	(0)	0.0	(0)	10.5	(2)
	West Atlantic	27.4 (19)	24.9 (18)	21.0 (17)	15.0 (16)	4.6	(8)	5.0	(4)	2.1	(2)	0.0	(0)
	East Atlantic	5.9	(1)	29.4	(2)	8.8	(1)	11.8	(1)	0.0	(0)	14.7	(1)	14.7	(1)	14.7	(1)
	Overall	26.4 (27)	24.4 (25)	17.5 (21)	13.5 (20)	5.0 (11)	4.7	(5)	2.8	(3)	5.7	(5)
	† Threat added by survey participants
	mammalian eradication are high (Samaniego-Herrera et al. 2013),
	and recovery of seabird colony ecosystems and seabird
	populations after mammal eradication can take decades
	(Drummond and Leonard 2010, Jones 2010; but see Jones et al.
	2016).

Acknowledgments:

ILP was funded by a MITACS fellowship. We thank S. Oppel and an anonymous reviewer for their valuable feedback that greatly improved the manuscript. Additional assistants, collaborators, and funding agencies are listed in publications of the coauthors. We thank H. Renner and S. C. Votier for responding to the survey.

 44) 3 ( 27) 4 ( 22) 2 ( 11) 1 ( 6)

Southern stormpetrels 9 2 ( 22) 5 ( 56) 0 (0.0) 0 (0) 1 ( 11) 1 ( 11) Total 27 2 (7.5) 13 ( 48) 3 ( 11) 4 ( 15) 3 ( 11) 2 (7.5)