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The destructiveness of major (Category 3 to 5) hurricanes along the United States Atlantic Ocean seaboard has been recognized for centuries. While the effects of hurricanes on coastal ecosystems are well known, the influence of hurricanes on pelagic seabirds is difficult to assess. During the annual Atlantic hurricane season ( similar to 1 June to 30 November), the endangered black-capped petrel Pterodroma hasitata aggregates in Gulf Stream habitats from Florida to North Carolina. On at least 8 occasions over the past century, hurricanes have driven petrels far inland (sometimes as far as the Great Lakes), suggesting the demise of 10s to 100s of individuals. This paper models >100 yr of data to characterize and compare key aspects of hurricanes that did and did not drive petrels inland. Our model suggests that the predicted increase in the frequency of Category 3 to 5 hurricanes in the region due to climate change could nearly double the expected number of wrecked petrels over the next century and place an endangered species at greater risk of extinction.

The Black-capped Petrel or Diablotin Pterodroma hasitata has a fragmented and declining population estimated at c.1,000 breeding pairs. On land, the species nests underground in steep ravines with dense understorey vegetation. The only confirmed breeding sites are located in the mountain ranges of Hispaniola in the Caribbean, where habitat loss and degradation are continuing threats. Other nesting populations may still remain undiscovered but, to locate them, laborious in situ nest searches must be conducted over expansive geographical areas. To focus nest-search efforts more efficiently, we analysed the environmental characteristics of Black-capped Petrel nesting habitat and modeled suitable habitat on Hispaniola using openly available environmental datasets. We used a univariate generalized linear model to compare the habitat characteristics of active Black-capped Petrel nests sites with those of potentially available sites (i.e. random pseudo-absences). Elevation, distance to coast, and the influence of tree cover and density emerged as important environmental variables. We then applied multivariate generalized linear models to these environmental variables that showed a significant relationship with petrel nesting activity. We used the top performing model of habitat suitability model to create maps of predicted suitability for Hispaniola. In addition to areas of known petrel activity, the model identified possible nesting areas for Black-capped Petrels in habitats not previously considered suitable. Based on model results, we estimated the total area of predicted suitable nesting habitat for Black-capped Petrels on Hispaniola and found that forest loss due to hurricanes, forest fires, and encroachment from agriculture had severely decreased availability of predicted suitable habitat between 2000 and 2018.

Despite being listed as endangered, substantial morphological and behavioral variation exists within Black-capped Petrel (Pterodroma hasitata) populations. To examine the population genetic structure of the Black-capped Petrel, we amplified Cytochrome Oxidase 1 sequences from museum specimens collected during 1970–1980 off the coast of North Carolina, USA. These sequences revealed a 1.2% fixed genetic difference between dark and light morphs. Individuals with intermediate plumage all grouped phylogenetically with the light morph. Combined with significant differences in body size and phenology, our genetic results suggest breeding isolation of the dark and light morphs. Consistent with other Pterodroma species, our results imply that the Black-capped Petrel may comprise two distinct, reproductively isolated taxa. Further knowledge about the genetic identity of birds at specific nesting colonies will be valuable for geographic delineation of populations.

ABSTRACT The black-capped petrel (Pterodroma hasitata) is an endangered seabird endemic to the western north Atlantic. Although estimated at ~ 1,000 breeding pairs, only ~ 100 nests have been located at two sites in Haiti and three sites in the Dominican Republic. At sea, the species primarily occupies waters of the western Gulf Stream in the Atlantic and the Caribbean Sea. Due to limited data, there is currently not a consensus on the marine range of the species. There are several maps in use for the marine range of the species and these differ with respect to the north, south, and eastward extent of the range. None of these maps, however, includes the Gulf of Mexico. Here, we report on observations of black-capped petrels during two vessel-based survey efforts throughout the northern Gulf of Mexico from July 2010 - July 2011, and from April 2017 - September 2019. During the 558 days and 54.7 km of surveys from both efforts we tallied 40 black-capped petrels. Most observations occurred in the eastern Gulf, although birds were observed over much of the east-west and north-south footprint of the survey area. Predictive models indicated that habitat suitability for black-capped petrels was highest in areas associated with dynamic waters of the Loop Current, similar to habitat used along the western edge of the Gulf Stream in the western north Atlantic. We suggest that the range for black-capped petrels be modified to include the entire northern Gulf of Mexico although distribution may be more clumped in the eastern Gulf and patchier elsewhere. It remains unclear, however, which nesting areas are linked to the Gulf of Mexico. Competing Interest Statement The authors have declared no competing interest. Footnotes * ↵* email: pjodice{at}g.clemson.edu, Twitter @SCCoopUnit, @WSUChair

Eddies along the western frontal boundary of the Gulf Stream result in the episodic formation of physically and biologically distinct water masses at the continental shelf break (ca 200 m isobath) off the southeastern United States. Standardized counts of seabirds were made simultaneously with ship-board and satellite-derived (VHRR) hydrographic measurements in 3 eddy-associated water masses during July 1983, and in 4 water masses during August 1984. Two statistical models were used to test for significant relations between seabird species composition and these water masses. Contingency analyses of abundance data from both cruises revealed that seabird species were not distributed independently of water mass type (p < .005). Tested against the null hypothesis of homogeneous species' abundances, 85 % of common (densities ≥ 0.5 birds km⁻²) seabird species exhibited significant affinities for a single water mass. The aerially foraging and feeding black-capped petrel Pterodroma hasitata and bridled tern Sterna anaethetus were most abundant in oligotrophic Gulf Stream and warm filament water, respectively. Species foraging on the ocean surface and feeding for more prolonged periods, shearwaters Puffinus gravis and Calonectris diomedea and storm-petrels Oceanites oceanicus and Oceanodroma castro, were most abundant in the upwelled cold core of the eddy. Interspecific variation in seabird affinities for meso-scale (50 to 150 km) water masses can be attributed to trophic segregation originating from species-specific foraging behaviors, and oceanographic processes that directly or indirectly influence prey availability. These patterns indicate that apex marine consumers parallel other taxa and trophic groups in their responses to environmental heterogeneity induced by western boundary currents. Gulf Stream frontal eddies persist at 'event' time scales (2 to 14 d), thereby further suggesting that some seabirds are functionally integrated with marine communities affiliated with relatively small, ephemeral, and kinetic physical features.

Remote sensing techniques such as radar altimetry, synthetic aperture radar, coastal zone color scanning, and infrared radiometry provide effective, instantaneous, and relatively inexpensive means for characterizing critical habitats of marine birds. In order to make optimal use of satellite-derived data, the rationale for marine habitat classification is presented, and advantages and limitations of different remote sensing techniques are discussed. An application of remote characterization is used to test for short-term habitat use and selection by the Black-capped Petrel (Pterodroma hasitata). By combining synoptic satellite mapping (e.g., infrared radiometry) with ship-board censusing, it was possible to demonstrate that petrels did not use all marine habitats equally, nor did petrels use habitats in proportion to their availability (areal extent).

Recent seabird surveys off the coast of the southeastern United States indicate that petrel distribution is most influenced by the Gulf Stream and other warm water masses between 10° and 40°N latitude. Gulf Stream meandering and topographically induced current deflection affected petrel distribution at meso-scales (100-1000 km) between Florida and North Carolina. Locally (10-100 km), petrel distribution was influenced by the presence of upwelling associated with Gulf Stream eddies and the mesas, ridges, and hills on the Blake Plateau. Sea surface temperature and depth alone did not adequately characterize the petrel's marine habitat. Petrels used three modes of flight, and their flight behavior was strongly influenced by wind speed. During the day they were most active in early morning and late afternoon, when all observed feeding took place. Petrels also may have fed crepuscularly and at night. Most feeding occurred in mixed species flocks at either natural food sources (fish and invertebrate swarms) or on chum at fishing vessels. Petrels did not rely exclusively on olfaction for locating food sources. They fed on cephalopods, small fish, and fauna associated with the macro-alga Sargassum.