Carter et al.: Introduction — Ashy Storm-Petrel conservation and science 53 RANGE-WIDE CONSERVATION AND SCIENCE OF THE ASHY STORM-PETREL OCEANODROMA HOMOCHROA HARRY R. CARTER1, DAVID G. AINLEY2, SHAYE G. WOLF3 & ANNA M. WEINSTEIN4 1Carter Biological Consulting, 1015 Hampshire Road, Victoria, BC V8S 4S8, Canada ([email protected]) 2H.T. Harvey and Associates, 983 University Avenue, Los Gatos, CA 95032, USA 3Center for Biological Diversity, 1212 Broadway, Suite 800, Oakland, CA 94612, USA 4California Audubon, 220 Montgomery Street, Suite 1000, San Francisco, CA 94104, USA Received 3 July 2015, accepted 17 February 2016 SUMMARY CARTER, H.R., AINLEY, D.G., WOLF, S.G. & WEINSTEIN, A.M. 2016. Range-wide conservation and science of the Ashy Storm-Petrel Oceanodroma homochroa. Marine Ornithology 44: 53–62. In February 2015, a special paper session about the range-wide conservation and science of the Ashy Storm-Petrel Oceanodroma homochroa (ASSP) was held at the Pacific Seabird Group annual meeting. The main goal was to share information amassed during the past 20 years on this species, which breeds almost entirely in California, United States, for formulating future research and conservation actions. One key result is the six papers on ASSP and two on Leach’s Storm-Petrels O. leucorhoa in this issue of Marine Ornithology. In this introduction, we augment contributed papers with a summary of historic and recent knowledge about the ASSP breeding range, key conservation issues and data gaps. The largest breeding concentration is at the South Farallon Islands in central California, but four other concentrations occur in southern California at the Channel Islands (Prince, Santa Barbara-Sutil, northwest Santa Cruz and northeast Santa Cruz). Over the past two centuries, many ASSP breeding colonies have been affected by introduced mammals and human-altered breeding habitats. Population decline due to heavy avian predation has been documented at the South Farallon Islands since 1972; decline due to eggshell thinning from organochlorine pollutants is suspected in the Channel Islands since the 1950s. Eradication of introduced mammals, reduction of pollution and social attraction (vocalization broadcasting and artificial nest sites) have helped to restore population size at certain colonies. Key words: Ashy Storm-Petrel, Oceanodroma homochroa, California Current, introduced predator, Leach’s Storm-Petrel, Oceanodroma leucorhoa, organochlorine pollution, population decline, seabird restoration INTRODUCTION (Ainley 1995). To share more recently acquired knowledge about status, natural history, conservation and restoration from The Ashy Storm-Petrel Oceanodroma homochroa (hereafter, ASSP) different parts of the breeding range and to promote publication is endemic to the California Current System (CCS) and breeds of recent findings, a special paper session, “Ashy Storm-Petrel among the limited number of islands and coastal rocks available range-wide conservation and science,” was held at the annual along the coasts of California, United States, and northwestern meeting of the Pacific Seabird Group in San Jose, California, Baja California, Mexico, between 41°N and 32°N (Ainley 1995, on 20 February 2015. Three of nine presentations in that paper Carter et al. 2008a, 2015a, Howell 2012). The global breeding session are published in this issue of Marine Ornithology (Adams population is only roughly known, as is true with most crevice- 2016, Becker et al. 2016, McIver et al. 2016), and two have and burrow-nesting seabird species, and is currently thought to been published elsewhere (Carter et al. 2015a, Nur et al. in be about 5 000 pairs, concentrated at five main breeding areas in press). In addition, two other papers about ASSP not presented central and southern California (Fig. 1). This storm-petrel has at the meeting (Harvey et al. 2016, Mills 2016) and two others received increased attention since 1970, with much effort focused about Leach’s Storm-Petrels O. leucorhoa (LESP) in southern on its breeding biology, status, distribution and conservation. The California (Adams et al. 2016, Carter et al. 2016) are included species is considered endangered and declining by the International in this issue. This group of peer-reviewed papers on ASSP and Union for the Conservation of Nature (IUCN 2015), and in Mexico LESP will (1) assist researchers, agencies and private groups it has been listed at the federal level as threatened. In 2002, the to understand and manage these species throughout the CCS; US Fish and Wildlife Service (USFWS) listed it as a Bird of (2) contribute to future status assessments by federal and state Conservation Concern (USFWS 2002). In 2009 and 2013, USFWS agencies; and (3) help to guide future conservation efforts. also completed status reviews to evaluate its potential listing under As background for these papers, we summarize historical the US Endangered Species Act but decided against doing so and current knowledge of confirmed breeding colonies and (USFWS 2009, 2013). The State of California considers it a Species key conservation issues related to these colonies. In addition, of Special Concern (Carter et al. 2008a) but has not considered it we clarify locations with reported but unconfirmed breeding, for possible listing as threatened under the California Endangered occurrences near potential breeding habitats that may indicate Species Act. undetected breeding, and areas where additional colony surveys are needed. A separate effort is underway to collate and analyze Little peer-reviewed literature about ASSP has been produced since at-sea data, which will be useful in examining at-sea conservation 1995, when the Birds of North America account was published issues (D.G. Ainley, unpubl. data). Marine Ornithology 44: 53–62 (2016) 54 Carter et al.: Introduction — Ashy Storm-Petrel conservation and science BREEDING DISTRIBUTION species (see summaries in Ainley & Lewis 1974, Ainley 1995, Carter et al. 2008a). Breeding biology and long-term monitoring of In the 1970s and 1980s, most of the world population of ASSP natural history patterns, avian predation and trends in colony size was thought to breed at the South Farallon Islands (hereafter, have been studied at the Farallones since 1971 (Ainley et al. 1974, “Farallones”) in the central CCS. The species description in 1864 1990a, Sydeman et al. 1998, Nur et al. in press). was based on specimens from the Farallones (Coues 1864), and breeding was first documented there in 1885 (Ingersoll 1886). Ironically, breeding by this species was first documented in the Dozens of naturalists subsequently described nesting in rock California Channel Islands (CCI) in 1875 at San Miguel Island crevices and human-constructed rock walls and other structures; (most likely Prince Island), 11 years earlier than at the Farallones burrows are not excavated in soil as in many other storm-petrel (Henshaw 1876; Carter et al. 2016). Breeding was documented (i.e., Fig. 1: Confirmed breeding locations (black dots) of the Ashy Storm-Petrel in California, United States, and Baja California, Mexico (updated from Carter et al. 1992, 2008a). Other locations mentioned in the text also are indicated. Marine Ornithology 44: 53–62 (2016) Carter et al.: Introduction — Ashy Storm-Petrel conservation and science 55 eggs, chicks or incubating adults) at four CCI over a prolonged at the Coronado Islands in 1895–1902, when many nests of LESP period: Santa Cruz Island — 1912 (Wright & Synder 1913); Santa and Black Storm-Petrels O. melania (BLSP) were first described Barbara Island (including Sutil Island) — 1976 (Hunt et al. 1979, (e.g., Anthony 1898, Grinnell & Daggett 1903). Between 1968 and 1980); San Clemente Island — 1996 (adult in incubating posture) 1991, low numbers of ASSP were captured in mist nets, and it was and 2013 (adult incubating an egg; Carter et al. 2008a, 2009; Carter considered to be a rare breeder (Jehl 1977, Everett & Anderson & Henderson 2015); and Anacapa Island — 2011 (Harvey et al. 1991). Greater numbers were reported breeding in 2005 (Carter et 2016). However, breeding was first suspected at Santa Barbara al. 2006a, 2008a), but in retrospect it was difficult or impossible Island as early as 1904, when many ASSP came aboard the fishery to distinguish many ASSP from dark-rumped LESP when viewed research vessel Albatross anchored offshore (Miller 1936). At Santa (often incompletely) inside crevices (Carter et al. 2016; H.R. Carter, Catalina Island, a historical ASSP breeding record (egg collected) unpubl. data). One storm-petrel nest found at Todos Santos Islands exists for 1937 (Carter et al. 2008a), but was likely a nest of a (31.8°N) on 7 May 2005 was initially thought to be ASSP (Carter et misidentified dark-rumped LESP (Carter et al. 2016). ASSP also al. 2006b, 2008a), but in retrospect it too could well have been that do not breed at San Nicolas Island. Among the CCI, long-term of a dark-rumped LESP (Carter et al. 2016). More work is needed monitoring of natural history patterns, avian predation and trends to document breeding and assess population sizes of ASSP, LESP in colony size have been in place at only five colonies at northwest and BLSP at the Coronado and Todos Santos islands. and northeast Santa Cruz Island since 1995 (McIver 2002; McIver et al. 2009, 2016). At four of these colonies, ASSP nest within sea There is only one verified specimen record of ASSP at a possible caves in rock crevices, in cavities beneath driftwood and in open breeding colony south of Todos Santos Islands. On 13 April 1951, a sites (McIver 2002, McIver et al. 2016). At other CCI colonies, specimen (Los Angeles County Museum #51880) was collected by nests are in rock crevices on small rocks or islets or on steep slopes W.V. Mayer at the anchorage at San Martin Island (30.5°N), after and cliffs on larger islands, and, to some degree, in empty Cassin’s it flew aboard the fishery research vessel Velero IV, likely attracted Auklet Ptychoramphus aleuticus burrows at Prince Island (Hunt et by the vessel’s lights.