Oceanodroma Homochroa Research Articles

Evaluating population impacts of predation by owls on storm petrels in relation to proposed island mouse eradication

AbstractWe quantify the expected demographic benefit to a seabird of conservation concern, the ashy storm‐petrel Oceanodroma homochroa, from the proposed eradication of introduced house mice Mus musculus on the South Farallon Islands, California. A key objective of the eradication is to reduce storm petrel predation by burrowing owls Athene cunicularia, which stopover on the island during their fall migration. Mouse trapping and field surveys of both owls and depredated storm petrel carcasses conducted during 2000–2012 reveal a strongly seasonal, inter‐related pattern among the three species: When owls arrive during the fall, mice are super‐abundant and the overwhelming choice of prey for those owls that remain. In the winter, the mouse population crashes just as storm petrels begin to arrive in large numbers; owls that remain on the island switch to preying upon storm petrels until May, when they depart to breed. Capture–recapture analyses of storm petrels showed (1) annual adult survival was inversely related to owl abundance, especially during January–April, and (2) storm petrels demonstrated a declining trend in abundance 2006–2012. The latter was associated with low rates of adult survival, high abundance of overwintering burrowing owls, and high incidence of depredated storm petrels. To evaluate projected impacts to storm petrels of a change in owl predation, we developed a Leslie matrix model, incorporating environmental stochasticity. We modeled future storm petrel population trajectories, allowing for different levels of owl‐mediated predation. Our results suggest that a reduction in owl abundance, a projected consequence of the elimination of mice, has the potential to substantially reduce overall storm petrel mortality, thereby reducing storm petrel declines and increasing the likelihood of stable trends in the future. While long‐term benefits to storm petrels of mouse eradication are apparent, the risk of increased predation due to prey‐switching by owls also needs to be addressed. This study highlights uncertainty of outcomes, which must be considered in evaluating management impacts. This study demonstrates the value of concurrent, continuous, long‐term datasets in providing a quantitative basis for management to aid the conservation of species of concern.

Avian and Skunk Predation of Ashy Storm-Petrels at Santa Cruz Island, California

Avian and mammalian predation of Ashy Storm-Petrels (Oceanodroma homochroa) were documented during monthly nest monitoring in 1995–1998 and 2005–2015 and once-per-year monitoring in 1999–2004 at 5 colonies at Santa Cruz Island, California. Throughout the study period, predation by Barn Owls (Tyto alba) was documented at the sea cave colonies, and at Orizaba Rock, and likely contributed to reduced breeding success at Bat Cave in 1995–1997. Recent predation by Common Ravens (Corvus corax) caused reduced breeding success each year in 2012–2015 at Orizaba Rock (35%–48%) and in 2013 and 2015 at Bat Cave (49%–52%). Raven predation appears to be developing into a larger long-term problem that may require additional management actions, but efforts have focused on deploying artificial nests at Bat Cave to provide more protected sites. Two sea cave colonies where skunks previously had not been detected experienced major adult mortality due to unusual predation events by island spotted skunks (Spilogale gracilis amphiala) in 2005 and 2008. At Bat Cave in 2005, 2 skunks were trapped after they had killed at least 76 Ashy Storm-Petrel adults. Prior to this mortality event, the colony contained 64–97 nests per year in 1995–1997, with low breeding success (49%–59%) related largely to organochlorine pollutants. After the skunks were caught, nest numbers increased from 19 in 2006 to 100 in 2015, with variable but generally higher breeding success (49%–90%). At Cavern Point Cove Caves in 2008, 2 skunks were trapped after killing at least 32 adults. Prior to the mortality event, this colony contained 11–17 nests per year in 1995–1997, with a lower breeding success rate of 20%–47%. Nest numbers increased from 2 in 2009 to 10 in 2015, with a variable but higher rate of breeding success (50%–80%). Skunk predation events may have been related to temporarily higher skunk populations at Santa Cruz due to low numbers of island foxes (Urocyon littoralis santacruzae). Deer mice (Peromyscus maniculatus santacruzae) were not significant predators of Ashy Storm-Petrels at Santa Cruz Island.

Status of Ashy Storm-Petrel Breeding Colonies at Santa Cruz Island, California, 1912–1998

We summarized historical knowledge from 1912 to 1998 of 13 known breeding colonies of Ashy Storm-Petrels (Oceanodroma homochroa) at Santa Cruz Island, California. Breeding was first reported by naturalists at Painted Cave (1912), Scorpion Rocks (1928), and Orizaba Rock (1937). During early seabird colony surveys of the Channel Islands, breeding was also noted at Cavern Point Cove Caves (1970), Diablo Rocks (1976), and Gull Island (1977). During 1991–1998, more extensive surveys of nearly all sea caves and offshore rocks documented additional breeding at Bat Cave, Cave of the Birds' Eggs, Del Mar Cove Cave, Del Mar Rock, Dry Sandy Beach Cave, Shipwreck Cave, and Willows Anchorage Rocks. Historical impacts apparently occurred from specimen collecting and interference by other nesting seabirds; however, guano harvesting may have had major impacts on nesting habitats at Scorpion Rocks (main rock) and Orizaba Rock. Impacts from organochlorine pollutants were likely extensive, and population sizes at all colonies may have been lower in the 1960s and 1970s when organochlorine pollution was at its highest level. Standardized monthly nest monitoring during 1995–1998 was used to measure reproductive success and population size at 5 colonies, creating a baseline for long-term trend monitoring that has continued annually to 2016. Mist net captures were used to estimate population sizes at 2 colonies in 1991. Estimated population size for Santa Cruz Island in 1991–1998 was 338 pairs, greater than previously reported for 1976–1977 (45–55 pairs), but the more recent estimate includes more colonies (especially 3 large colonies in sea caves), different methods of estimation, and likely some recovery from impacts associated with organochlorine pollution.

Genome Sequence of a Gyrovirus Associated with Ashy Storm-Petrel.

Ashy storm-petrels (order Procellariiformes) are seabirds that are found along the coast of California to Baja Mexico. A novel gyrovirus was identified from a cloacal swab of an ashy storm-petrel, which is the second gyrovirus to be identified in sea birds, the first being found in the related northern fulmar.

Collision and displacement vulnerability to offshore wind energy infrastructure among marine birds of the Pacific Outer Continental Shelf

Marine birds are vulnerable to collision with and displacement by offshore wind energy infrastructure (OWEI). Here we present the first assessment of marine bird vulnerability to potential OWEI in the California Current System portion of the U.S. Pacific Outer Continental Shelf (POCS). Using population size, demography, life history, flight heights, and avoidance behavior for 62 seabird and 19 marine water bird species that occur in the POCS, we present and apply equations to calculate Population Vulnerability, Collision Vulnerability, and Displacement Vulnerability to OWEI for each species. Species with greatest Population vulnerability included those listed as species of concern (e.g., Least Tern [Sternula antillarum], Marbled Murrelet [Brachyramphus marmoratus], Pink-footed Shearwater [Puffinus creatopus]) and resident year-round species with small population sizes (e.g., Ashy Storm-Petrel [Oceanodroma homochroa], Brandt's Cormorant [Phalacrocorax penicillatus], and Brown Pelican [Pelecanus occidentalis]). Species groups with the greatest Collision Vulnerability included jaegers/skuas, pelicans, terns and gulls that spend significant amounts of time flying at rotor sweep zone height and don't show macro-avoidance behavior (avoidance of entire OWEI area). Species groups with the greatest Displacement Vulnerability show high macro-avoidance behavior and low habitat flexibility and included loons, grebes, sea ducks, and alcids. Using at-sea survey data from the southern POCS, we combined species-specific vulnerabilities described above with at-sea species densities to assess vulnerabilities spatially. Spatial vulnerability densities were greatest in areas with high species densities (e.g., near-shore areas) and locations where species with high vulnerability were found in abundance. Our vulnerability assessment helps understand and minimize potential impacts of OWEI infrastructure on marine birds in the POCS and could inform management decisions.

Burrowing Owl Diet at a Migratory Stopover Site and Wintering Ground on Southeast Farallon Island, California

Abstract On the Farallon Islands, 48 km west of the coast of central California, Burrowing Owls (Athene cunicularia) are a native migrant and a predator of the nonnative house mouse (Mus musculus) and the native Ashy Storm-Petrel (Oceanodroma homochroa). Previous research showed that Burrowing Owl predation on Ashy Storm-Petrels is likely unnaturally exacerbated by the abundance of house mouse prey in the fall, which may encourage more owls to overwinter. When the cyclic mouse population crashes in winter, the owls switch to preying upon the storm-petrels, a species of conservation concern. From September 2010 to May 2011, we conducted daily owl surveys and a diet study of Burrowing Owls on Southeast Farallon Island. One goal was to document seasonal changes in Burrowing Owl diet composition through collection and assessment of pellets. During our study period, 12 banded owls overwintered for an average of 118 d and contributed 64% of the 679 analyzed owl pellets. Insects were the most numerous prey item ...

Response of Native Species 10 Years After Rat Eradication on Anacapa Island, California

Abstract Measuring the response of native species to conservation actions is necessary to inform continued improvement of conservation practices. This is particularly true for eradications of invasive vertebrates from islands where up-front costs are high, actions may be controversial, and there is potential for negative impacts to native (“nontarget”) species. We summarize available data on the response of native species on Anacapa Island, California, 10 y after the eradication of invasive black rats Rattus rattus. Native marine taxa hypothesized to respond positively to rat eradication increased in abundance (Scripps's murrelet Synthliboramphus scrippsi; International Union for Conservation of Nature Vulnerable, and intertidal invertebrates). Two seabird species likely extirpated by rats—ashy storm-petrel Oceanodroma homochroa (International Union for Conservation of Nature Endangered) and Cassin's auklet Ptychoramphus aleuticus—are now confirmed to breed on the island. Long-term negative effects from nontarget impacts are limited. Rufous-crowned sparrows Aimophila ruficeps obscura are still present, although likely in lower abundance. The endemic Anacapa deer mouse Peromyscus maniculatus anacapae population increased with no loss in heterozygosity, but with reduced genetic differentiation on East Anacapa and the loss of some alleles across the islets. Intertidal invertebrate cover increased while algal cover decreased. These findings clarify the pervasive effects of invasive rats on a wide variety of taxa, the short- and long-term impacts of eradication, and the ability of some island fauna to passively recover following a carefully planned rat-eradication project.

A wireless acoustic sensor network for monitoring wildlife in remote locations

Seabirds are the most threatened marine group with nearly 28% of extant species considered at risk of extinction. Managers and researchers face considerable financial and logistical challenges when designing programs to monitor the status of any of the 97 species listed as critically endangered, endangered, or vulnerable by the IUCN. These challenges are exacerbated by the fact that these birds breed in isolated/inaccessible locations, many have cryptic nest sites, and most return to colonies only at night. Acoustic sensors are an effective tool for monitoring the presence, distribution, and relative abundance of rare and elusive seabirds. We have developed new, cellphone-based wireless acoustic sensors that 1) are comparable to state-of-the-art sensors, 2) are affordable (~US$500.00 per hectare), 3) can sample continuously over months, 4) can telemeter data from remote locations via a cellular, microwave, or satellite link, and 5) can be reprogrammed remotely. To date we have deployed our wireless acoustic sensor networks to monitor seabirds of conservation concern including - Ashy Storm-petrel, Oceanodroma homochroa, on Southeast Farallon Island (CA), Tristram’s Storm-petrel, O. tristrami, on Tern Island (French Frigate Shoals), as well as Newell’s Shearwater, Puffinus newelli, and Hawaiian Petrel, Pterodroma sandwichensis, at the Upper Limahuli Preserve (Kaua’i, HI).

Top-down and bottom-up factors affecting seabird population trends in the California current system (1985–2006)

To characterize the environmental factors affecting seabird population trends in the central portion of the California current system (CCS), we analyzed standardized vessel-based surveys collected during the late spring (May–June) upwelling season over 22 yr (1985–2006). We tested the working hypothesis that population trends are related to species-specific foraging ecology, and predicted that temporal variation in population size should be most extreme in diving species with higher energy expenditure during foraging. We related variation in individual species abundance (number km −2) to seasonally lagged (late winter, early spring, late spring) and concurrent ocean conditions, and to long-term trends (using a proxy variable: year) during a multi-decadal period of major fluctuations in the El Niño-Southern oscillation (ENSO) and the Pacific decadal oscillation (PDO). We considered both remote (Multivariate ENSO Index, PDO) and local (coastal upwelling indices and sea-surface temperature) environmental variables as proxies for ocean productivity and prey availability. We also related seabird trends to those of potentially major trophic competitors, humpback ( Megaptera novaeangliae) and blue ( Balaenoptera musculus) whales, which increased in number 4–5-fold midway during our study. Cyclical oscillations in seabird abundance were apparent in the black-footed albatross ( Phoebastria nigripes), and decreasing trends were documented for ashy storm-petrel ( Oceanodroma homochroa), pigeon guillemot ( Cepphus columbus), rhinoceros auklet ( Cerorhinca monocerata), Cassin’s auklet ( Ptychoramphus aleuticus), and western gull ( Larus occidentalis); the sooty shearwater ( Puffinus griseus), exhibited a marked decline before signs of recovery at the end of the study period. The abundance of nine other focal species varied with ocean conditions, but without decadal or long-term trends. Six of these species have the largest global populations in the CCS, and four are highly energetic, diving foragers. Furthermore, three of the diving species trends were negatively correlated with the abundance of humpback whales in the study area, a direct competitor for the same prey. Therefore, on the basis of literature reviewed, we hypothesize that the seabirds were affected by the decreasing carrying capacity of the CCS, over-exploitation of some prey stocks and interference competition from the previously exploited, but now increasing, baleen whale populations. Overall, our study highlights the complexity of the ecological factors driving seabird population trends in the highly variable and rapidly changing CCS ecosystem.

A Potential New Colony of Ashy Storm-petrels on the Mainland Coast of California, USA

Abstract We report evidence of likely nesting of the Ashy Storm-petrel (Oceanodroma homochroa) on islets adjacent to Vandenberg Air Force Base in northern Santa Barbara County, California, USA. Ten storm-petrels, along with extensive suitable habitat in the area, suggest a small colony of breeding birds. Other offshore islets along California’s central coast might hold small numbers of storm-petrels. In addition, there are possibly breeding storm-petrels in suitable remote mainland areas, such as at Vandenberg Air Force Base.

Status and Trends of the Ashy Storm-Petrel on Southeast Farallon Island, California, Based upon Capture-Recapture Analyses

We conducted a capture-recapture study on the population size and trends of the Ashy Storm-petrel (Oceanodroma homochroa) on Southeast Farallon Island (SEFI), California, based upon data collected in 1971, 1972, and 1992. From March through August, birds were lured to fixed-site sampling locations using taped vocalization playback. Using program JOLLY, we estimated population size and evaluated statistical models using goodness-of-fit and Likelihood Ratio tests. On the southwestern slope of Lighthouse Hill, amidst prime breeding habitat, numbers of breeding birds decreased from 1,271 ± 140 (x ± SE) in 1972 to 710 ± 117 in 1992, a decline of 44% (approximate 95% CI = 22-66% decline; λ = -2.8% per annum); for a variety of reasons, we consider this to be the most reliable indicator of population change. In 1971, on a portion of SEFI relatively disjunct from the sampling area in 1972, 2,131 ± 322 breeding birds were estimated. To produce an overall early 1970s estimate with which to compare to 1992, we summed population estimates from 1971 and 1972. An overall value of 6,461 birds, of which 3,402 (53%) were breeders, was obtained for the early period. In 1992, the overall population in roughly the same area was estimated at 4,284 ± 409 birds, of which 1,990 ± 408 (46%) were presumed breeders. These results, encompassing peripheral as well as more centrally located storm-petrel habitat, indicate an overall population decline of 34% and a comparable decline in breeding birds of 42% over the past two decades. However, oceanographic conditions varied between 1971-1972 and 1992, and reduced food availability in 1992 may have influenced colony attendance and breeding effort. Nonetheless, the apparent population decline over the past 20 years suggests that the species warrants management and/or additional protective status.

High levels of cadmium in Atlantic seabirds and sea-skaters.

THE possibility that cadmium may be an environmental pollutant has caused concern because it has toxic effects on many animal species including man, rat, rabbit, chicken, quail, and pigeon1–4. The occurrence of cadmium in wildlife is not unusual and samples of marine species taken from around the British coast contain low levels (less than 0.5 mg per kg in fish and less than 2 mg per kg in most shellfish); however, levels of up to 93 mg per kg were present in limpets, Patellasp., collected from areas of natural mineralisation or industrial sources of cadmium5. Seabirds generally contain higher residues than marine invertebrates. For example, Anderlini et al.6 examined the amounts of nine metals in the livers of seven Antarctic and Pacific seabird species and noted that the maximum mean cadmium residue occurred in 10 ashy petrels Oceanodroma homochroa collected from their breeding grounds in California (mean residue was 53.2±20.5 mg per kg). Parslow et al.7 found up to 22.3 mg per kg dry wt cadmium in livers of eight puffins Fratercula arctica collected live from various British breeding colonies. It was suggested that pelagic birds might contain higher residues than coastal living species because a single fulmar Fulmarus glacialis examined by them contained 159 mg per kg cadmium. Anderlini et al. concluded that there was a correlation between increased concentration of cadmium in birds and exposure to industrial influences. Parslow et al. did not attempt to explain the residues they found in puffins, but Bourne8 concluded that individual birds were becoming increasingly contaminated through feeding near areas of local pollution around the British coast. It is debatable whether cadmium should be regarded as a pollutant to seabirds. We report here the occurrence of cadmium residues in the tissues of apparently healthy, breeding seabirds which are considerably higher than any previously found. More important, we conclude that the cadmium has a natural rather than an industrial origin, since we have found high cadmium residues in a marine insect, Halobates, which is widely distributed in tropical regions far from sources of industrial cadmium. This insect is only one example of the sources from which birds obtain their cadmium residues.

Shell-Thinning in Eggs of the Ashy Petrel (Oceanodroma homochroa) from the Farallon Islands

Shell-Thinning in Eggs of the Ashy Petrel (Oceanodroma homochroa) from the Farallon Islands

The Ornithological Writings of Chester Barlow

D URING the even decade of Chester 'Barlow's activity along literary lines more than fifty articles appeared to his credit, besides recently numerous editorials and short notes. His first article that I have found came to print in August, I902, in Lattin's Oologist where so many of us younger bird-students received our first inspiration to write up what we had learned. This first article of Barlow's was on the nesting of the ashy petrel on the Farallone Islands. He had visited these fascinating bird-islands and his discoveries there served also for several subsequent papers of remarkable interest to their younger readers, who longed to get to the oologist's paradise that was so vividly depicted. In 1893, within a few months after the founding of the Cooper Ornithological Club, its began to appear regularly in Taylor's Nidiologist. These reports were compiled largely from papers presented at the meetings. Here Barlow's good judgment and literary talent came into play in culling and compiling from the heterogeneous and often poorly-composed manuscripts those accounts we still find so full of interest. These Secretary's Reports continued for nearly four years, and are yet of high value for reference in regard to the life-histories of many western birds. During this period many signed articles also appeared dealing with bird-life in Santa Clara county. Here we find valuable articles on the nesting of the white-tailed kite and golden eagle. Then came the summer-vacation trips to the Sierra Nevada, and the delightful articles relating to its bird-life, not only pleasing, but of permanent value to science-important additions to the known histories of such birds as the hermit warbler, Calaveras warbler, olive-sided flycatcher and Cassin Vireo. With the inauguration of the Bulletin of the Cooper Ornithological Club in January, 1899, Barlow's really most important service to ornithology began, though his own signed articles became fewer. We probably never can sufficiently realize the great influence Barlow exerted in bringing out previously unknown observersurging them to contribute from their own stock of knowledge, and thus instilling that enthusiasm which when once well started may in time lead into the genius of a Coues. Barlow is not considered by some to have been a scientific ornithologist. He never wrote an article which was not intended for the merest beginner to read and enjoy. But I believe his career to have had a much more far-reaching influence on scientific ornithology than if he had entered, and confined his entire energy to, systematic or philosophic fields. 1892. The Ashy Petrel (Oceanodroma homochroa) on the Farallones. -Oologist IX, August 1892, pp. 193-194. 1892. Professional Egging; or the Collecting of Murre's Eggs in California. -Oologist IX, December 1892, pp. 255-257. 1893. A Day with the Creek Birds. -Am. Mag. of Natural Science I, May 1893, pp. 77-78. 1893. The White-tailed Kite and Prairie Falcon in California. -Oologist X, September 1893, PP. 258-260. 1893. Nesting of the Mallard Duck [near San Jose]. -Nidiologist I, November 1893, p. 38, 2 hftt. 1893. The Pileolated and Yellow Warblers [nesting in Santa Clara County]. -Nidiologist I, November I893, PP. 44-45. 1893. Nesting Habits of the Brandt's, Baird'sand Farallone Cormorants. -Am. Mag. of Nat. Science II, November 1893, pp. 53-54. 1893. Cooper Ornithological Club. [Secretary's Report, including notes on Lutescent Warbler, etc.] -Nidiologist I, December 1893, pp. 6o-6I. 1894. Collecting on the Farallone Islands. -Naturalist I, January I894, pp. 7-8.