Birdfinding.info ⇒ A widespread species, or species group, that is locally common in a few areas, but generally scarce across most of its wide distribution in warm waters of the Atlantic and Pacific Oceans. The winter-breeding North Atlantic form, “Grant’s”, is common around the Azores, Madeira, and Canary Islands from August to April, and fairly common in U.S. Gulf Stream waters and the Gulf of Mexico from May to August, when the summer-breeding “Madeiran” replaces it in Madeira and the Canaries. In the South Atlantic, the “Gulf of Guinea” and “St. Helena” forms are locally common around the remote islands where they breed. In the Pacific, “Darwin’s” is common year-round in the Galápagos, and both “Hawaiian” and “Japanese” can sometimes be found in waters adjacent to their breeding areas from April or May to November.
Band-rumped Storm-Petrel
Hydrobates castro
Breeds on tropical and subtropical islands in the Atlantic and Pacific Oceans; disperses to warm waters of both oceans.
Under its current (2022) classification, the Band-rumped Storm-Petrel consists of seven or more distinct forms that are potentially separate species: two that breed in the North Atlantic; two in the South Atlantic; and one each in the western, central, and eastern Pacific.
Approximate global distribution of the various forms of Band-rumped Storm-Petrel. © BirdLife International 2018
“Grant’s Storm-Petrel” (ssp. nova): breeds in the Azores, Madeira, Selvagens, Canaries, and Berlengas (beside Portugal) from August to April.
“Madeiran Storm-Petrel” (castro): breeds on Madeira, the Selvagens, and Canaries from late March to October.
“Gulf of Guinea Storm-Petrel” (ssp. nova): breeds in mountain forests of São Tomé, apparently year-round.
“St. Helena Storm-Petrel” (helena): breeds on islets around Ascension and St. Helena in seasonally segregated populations—from April to September and from October to March.
“Japanese Storm-Petrel” (kumagai): breeds on islets along the northeastern coast of Honshu from May to November.
“Hawaiian Storm-Petrel”, H. c. cryptoleucurus, near known breeding colony along the Na Pali Coast of Kauai. (August 23, 2012.) © Andre Raine
“Hawaiian Storm-Petrel” (cryptoleucurus): breeds on the main Hawaiian Islands (known mainly from Kauai and the Big Island) from April to November.
“Darwin’s Storm-Petrel” (bangsi): breeds in the Galápagos in seasonally segregated populations—from May to October and from December to May.
Nonbreeding. Although incompletely known, the available evidence indicates that a large portion of the “Grant’s Storm-Petrel” population—perhaps the majority—migrates west during April and May to spend the summer months in the Gulf of Mexico and Gulf Stream waters east of North America, where they molt and recover their strength, then depart around August.
The other three Atlantic forms are not known to migrate. Based on the molt-stage of some individuals and side-by-side comparisons with the predominant “Grant’s”, some of the band-rumped-type storm-petrels that occur each year in the Gulf Stream have been speculatively identified as “Madeiran”, but most such identifications are questionable—due to the difficulty of ruling out juvenile and first-year “Grant’s”, as well as Monteiro’s Storm-Petrel, which breeds around the same time as “Madeiran” (but on different islands) and has similar molt timing. Birds from “St. Helena” populations apparently disperse widely in the tropical mid-South Atlantic. Band-rumped-type storm-petrels presumed to belong to these populations have been observed between approximately 21° South and the Equator. The “Gulf of Guinea” form may be entirely sedentary.
“Japanese Storm-Petrel”, H. c. kumagai, seems to be the most likely identification (although “Hawaiian”, cryptoleurus, is also somewhat likely) of band-rumped-type storm-petrels found in the Coral Sea during March and April—such as this one, Australia’s first documented record of Band-rumped Storm-Petrel. (Offshore from Southport, Queensland, Australia; April 8-9, 2016.) Birdline Australia
All three Pacific forms appear to migrate or disperse over long distances. The “Japanese” and “Hawaiian” populations apparently vacate the breeding grounds from November to April. Recent records of band-rumped-type storm-petrels in the Tasman and Coral Seas during March and April likely to pertain to one or both of these forms—as both are generally absent from their known ranges at that time of year, and are therefore seem likely to migrate a substantial distance away from their breeding grounds. Finally, nonbreeding “Darwin’s” apparently disperses widely in the eastern Pacific, as it has been found regularly north to Costa Rican and Panamanian waters, south to the latitudes of southern Peru and west across the Pacific past the longitude of Easter Island.
Identification
A medium-large storm-petrel that is dark-brown overall, with an even white band across the rump that usually extends partway down the sides of the rump to the undertail.
The distinct forms, or cryptic species, are visually indistinguishable under most circumstances from one another and from other “band-rumped-type” storm-petrels recently recognized as separate species: i.e., Monteiro’s and Cape Verde. (See Notes below for a comparison of Atlantic band-rumped-type storm-petrels, including Monteiro’s and Cape Verde.)
“Grant’s Storm-Petrel”, H. c. ssp. nova—likely this form, in fresh plumage to begin the breeding season. (Banco de la Concepción, Canary Islands, Spain; September 2, 2017.) © Miguel Rouco
“Darwin’s Storm-Petrel”, H. c. bangsi, showing typical pattern and gliding flight posture. (Offshore south of Isla San Cristóbal, Galápagos, Ecuador; November 25, 2019.) © David M. Bell
The white rump-band varies somewhat in width and the extent to which it continues down the sides of the rump to the undertail coverts. These aspects vary within each form, and therefore have limited value in field identification of the forms—although some forms apparently tend to have narrower rump-bands (“Gulf of Guinea”) or more extensive white on the undertail (“St. Helena”).
“Grant’s Storm-Petrel”, H. c. ssp. nova—likely this form, in fresh plumage to begin the breeding season—note the exceedingly narrow white rump-band, a feature that seems to be subject to individual variation, not diagnostic of any North Atlantic form in the Band-rumped complex. (Banco de la Concepción, Canary Islands, Spain; August 17, 2014.) © Miguel Rouco
“St. Helena Storm-Petrel”, H. c. helena, ventral view showing white extending far down the sides of the undertail. (Offshore from St. Helena; April 18, 2018.) © John & Jemi Holmes
As a general rule, the tails of all forms have a shallow notch, but this feature varies within each form, and its appearance varies widely depending on posture and angle of view. In some cases, the same tail may appear notched, square-tipped, or even wedge-shaped.
“Madeiran Storm-Petrel”, H. c. castro, with tail appearing notched in this posture. (Offshore from Bugio, Madeira; June 8, 2011.) © Simon Colenutt
“Madeiran Storm-Petrel”, H. c. castro, with tail appearing wedge-shaped in this posture. (Offshore from Bugio, Madeira; June 8, 2011.) © Simon Colenutt
Juveniles and freshly molted adults have the most pronounced wingbars. On juveniles the bar appears white. On adults returning to the breeding grounds, the bar is blond. With feather-wear, the bar diminishes and can disappear entirely by the time the next molt begins.
“Grant’s Storm-Petrel”, H. c. ssp. nova, in worn plumage, molting its flight feathers, a condition that is effectively diagnostic of a post-breeding adult “Grant’s” at this season. (Offshore from Cape Hatteras, North Carolina; June 1, 2015.) © Michael Todd
“Hawaiian Storm-Petrel”, H. c. cryptoleucurus, with heavily worn wing-coverts showing weak diagonal bars. (Offshore from Kailua-Kona, Big Island, Hawaii; July 23, 2016.) © Annie B. Douglas / Cascadia Research Collective
Voice. Two types of calls are heard at breeding colonies: chattering and purring. The sounds are broadly similar from one population to another, but differences in patterns have been instrumental to understanding the relationships among similar-looking forms.
Among the North Atlantic forms, the calls of “Grant’s” and “Madeiran” are intermediate in length and complexity between the simpler Monteiro’s and more elaborate Cape Verde. Recordings are sparse or unavailable for most of the South Atlantic and Pacific populations, and would certainly illuminate the ongoing taxonomic review.
“Madeiran’s” chatter call is squeaky (like rapid rubbing of a fingertip on wet glass):
“Grant’s’” chatter call is similar, but has a consistent, distinguishing pattern, ending with two pairs of louder, sharper squeaks:
“Madeiran’s” purring call consists of a rapid purr or trill lasting about one to four seconds punctuated at the end by a quick flourish of sharp squeaks (as in the chatter call), often repeated many times in a row, without pausing:
“Grant’s’” purring call consists of a purr that builds for about 1.5 seconds then ends with a flourish of squeaks, the last two louder and sharper (like the ending of the chatter call, but once instead of twice):
(For detailed reviews of the North Atlantic forms’ vocal differences, with more recordings and sonograms, see The Sound Approach: Grant’s Storm-Petrel and The Sound Approach: Madeiran Storm-Petrel.)
The sparse recordings available for other populations suggest that they are vocally distinct from the North Atlantic forms.
In the equatorial South Atlantic, “Gulf of Guinea’s” chatter call is longer and more complex than the calls of other forms—except Cape Verde, which it resembles (implying that they may be closely related):
In the Pacific, “Hawaiian’s” chatter call is relatively short and simple, a stuttered or double-note followed by four to six distinct notes, and its purring call is a soft rattle or purr followed by two or three squeaky chatter notes.
Notes
Polytypic species consisting of seven or more subspecies—including at least two not formally described—all of which are distinct forms and potentially separate species. Eventually, it seems likely that the South Atlantic and Pacific forms will each be classified as one or more species separate from the North Atlantic forms.
All were formerly considered conspecific with Monteiro’s Storm-Petrel (monteiroi) and Cape Verde Storm-Petrel (jabejabe), which are now regarded as separate species based on genetic evidence of deep historical divergences in their lineages, vocal differences, and other evidence that they function as separate species despite overlapping distributions.
Howell and Zufelt (2019) provisionally recognize eight species among the populations currently classified as Band-rumped: “Grant’s” (sp. nova), “Madeiran” (castro), “Gulf of Guinea” (a.k.a. “São Tomé”, sp. nova), “St. Helena” (helena), “Japanese” (kamagai), “Hawaiian” (cryptoleucura), “Darwin’s” (bangsi), and “Spear’s” (sp. nova). The latter two forms refer to seasonally distinct breeding populations of the Galápagos, which are not known to be distinguishable except based on their egg-laying calendars.
A study published in 2019 (Taylor et al.) concluded that all of the Pacific forms were closely related to one another, but also to one of the South Atlantic forms (helena). The close affiliation of the Pacific populations to one another is not surprising, but their apparent affiliation with one Atlantic population presents an unanticipated complication. Another paper published in 2019 (Flood et al.) found indications that the “Gulf of Guinea” form might be more closely related to Cape Verde than to the other Band-rumped forms.
See below for a general comparison of the Atlantic members of the Band-rumped Storm-Petrel complex, and a specific comparison of “Grant’s Storm-Petrel” with Monteiro’s Storm-Petrel.
Cf. Other Atlantic Band-rumped-type storm-petrels. At least six cryptic species or forms in the Band-rumped Storm-Petrel complex have been recognized in the Atlantic. Four breed on North Atlantic archipelagos of Macaronesia and two on widely scattered islands of the South Atlantic. Apart from their breeding grounds, the ranges of these forms remain mostly unknown. Sightings are scarce and the forms are extremely difficult to distinguish from one another at sea.
The four North Atlantic forms overlap with one another to varying degrees and are known to differ vocally. In brief, all four have two similar call types—chattering and purring—which vary in length, pattern, and complexity. Differing calls have helped to confirm their respective breeding distributions, but they generally call only on the breeding grounds and only at night.
In most cases, under most conditions, the visual differences among the forms are too subtle and inconsistent for field identification. With that caveat, following is a summary of factors that might help in exceptional circumstances—the forms are listed by the average latitudes of their breeding grounds, from north to south.
Cape Verde Storm-Petrel—identification presumed based on the location, far out at sea south of Cape Verde, though any of the Atlantic band-rumped forms could occur there at any time of year. (May 4, 2011.) © Graham Ekins
“Madeiran Storm-Petrel”, H. c. castro —likely this subspecies, based on molt-stage, season, and location within its known breeding range—but these factors are also consistent with Monteiro’s, Cape Verde, and first-year “Grant’s”, all plausible alternative identifications. (Offshore northeast of Lanzarote, Canary Islands, Spain; November 1, 2014.) © Miguel Rouco
Monteiro’s Storm-Petrel—based on large samples of measured individuals at their Azorean breeding sites, Monteiro’s tends to have a more deeply notched tail than “Grant’s”, but their measurements overlap. (Offshore from Graciosa, Açores, Portugal; May 2011.) © Gareth Knass
“Gulf of Guinea Storm-Petrel”, H. c. ssp. nova, showing apparently thin rump-band and long-looking tail. © William H. Wagstaff
Monteiro’s Storm-Petrel (monteroi): Breeds in the Azores from March to October (eggs laid from early May to early July). Gives the shortest, simplest calls, with a rougher, scratchier quality than the others. Relatively small-bodied, long-tailed, and long-winged, and usually has a visibly notched tail.
“Grant’s Storm-Petrel” (ssp. nova): Breeds from the Azores east to the Berlengas and south to the Canaries from August to April (eggs laid from early October to early December). Calls end with signature punctuation. Relatively large and robust, and has a squarish or shallowly notched tail. Post-breeding adults show heavy feather-wear and/or molting flight feathers most noticeably from April to June—when Monteiro’s and “Madeiran” are fresh-plumaged.
“Madeiran Storm-Petrel” (castro): Breeds in Madeira, the Selvagens, and the Canaries from April to October (eggs laid in June and July). Calls are squeaky, rapid, about intermediate in length between Monteiro’s and Cape Verde, and lack the particular ending of “Grant’s”. Relatively small and slim overall; tail can appear either square-tipped or notched.
Cape Verde Storm-Petrel (jabejabe): Breeds in Cape Verde over an extended season, possibly year-round with two peaks—one from October into winter, the other from April into summer. Gives the longest, most complex calls, and genetic analyses indicate that it is the oldest divergent lineage in the band-rumped complex. Proportions are average, and has a squarish or shallowly notched tail.
“Gulf of Guinea Storm-Petrel” (ssp. nova): Breeds on São Tomé over an extended season, possibly year-round. Calls are relatively long and complex, suggesting an affinity with Cape Verde. Appears slightly larger than other forms, with a narrow white rump band and long-looking squarish or shallowly notched tail.
“St. Helena Storm-Petrel” (helena): Breeds on St. Helena and Ascension in two seasons—possibly multiple distinct forms or cryptic species—one from October to March, the other from April to September. Attends the nest diurnally. On some individuals the white rump band extends far down undertail coverts. Slightly larger than most other forms; usually shows a visibly notched tail.
Cf. Monteiro’s Storm-Petrel. Among the many populations of storm-petrels that were formerly classified together as Band-rumped, the first discovery of a “cryptic species” distinction was between the two populations that breed in the Azores: one in the hot season (Monteiro’s, which lays its eggs between early May and early July), the other in the cool season (“Grant’s”, which lays between early October and early December). Monteiro’s is not known to occur anywhere besides the Azores and surrounding seas, whereas “Grant’s” also breeds on other island groups east to the Berlengas and south to the Canaries, and migrates to the western North Atlantic and Gulf of Mexico.
Within the Azores, around their shared breeding grounds, Monteiro’s and “Grant’s” overlap en masse twice. First in spring, during March and April, both are present in the area: Monteiro’s arrives while “Grant’s” departs. Second in late summer, from mid-August into early October, both occur at the colonies, with “Grant’s” replacing Monteiro’s. At this time they have been observed in the same burrows—with “Grant’s” prospecting sites still occupied by fledgling Monteiro’s.
Due to the close relationship between them and the intensive research that led to their recognition as separate species, they have been compared more closely than other Band-rumped forms. See the biometric data compiled in Table 1, below, from Bolton et al. 2008—the paper that effectively proved their identities as separate species. Despite these robust comparisons, Monteiro’s and “Grant’s” can still be indistinguishable, even under optimal conditions.
Summarizing the differences: Monteiro’s averages slightly smaller in the body (e.g., weight and bill size), but slightly longer in the tail and wings. Tail fork depth is the most consistent visible differentiator, as Monteiro’s averages more than twice as deep: 7.81 mm for Monteiro’s versus 3.53 mm for “Grant’s”. Note that even these measurements overlap broadly (1 to 14 mm for Monteiro’s versus 0 to 7 mm for “Grant’s”), while all other recorded metrics overlap far more than they differ.
Table 1 from Bolton et al. 2008, comparing measurements of >100 “Grant’s Storm-Petrels” (the cool season population) and >200 Monteiro’s Storm-Petrels (the hot season population).
In spring and late summer in the Azores, Monteiro’s and “Grant’s” differ in their predominant molt-stages, although the differences are difficult to specify and apply. At the end of their breeding season, the adults of one population should appear either worn or visibly molting. Conversely, at the beginning of their breeding season, most adults of the other population should be near the middle of their cycle—not visibly worn, nor molting. These distinctions can be helpful in context, but several factors counsel against heavy reliance on molt-stage: i.e., the wide variability of feather-wear and replacement, along with the likely presence of some first-year birds and the possible presence of other Band-rumped forms.
Additional Photos of Band-rumped Storm-Petrel
“Grant’s Storm-Petrel”, H. c. ssp. nova. (Offshore from Cape Hatteras, North Carolina; June 8, 2018.) © Brian Sullivan
“Grant’s Storm-Petrel”, H. c. ssp. nova. (Offshore from Cape Hatteras, North Carolina; June 7, 2018.) © Brian Sullivan
“Grant’s Storm-Petrel”, H. c. ssp. nova. (Banco de la Concepción, Canary Islands, Spain; September 2, 2017.) © Miguel Rouco
“Hawaiian Storm-Petrel”, H. c. cryptoleucurus, showing typical flat-winged flight posture. (Offshore from Kailua-Kona, Big Island, Hawaii; September 2018.) © J. Bailey
“Grant’s Storm-Petrel”, H. c. ssp. nova. (Baía de Porto Pim, Faial, Azores; December 2, 2021.) © Andre Vieira
“Grant’s Storm-Petrel”, H. c. ssp. nova. (Isla Montaña Clara, Canary Islands; December 19, 2014.) © Stephen Menzie
“Grant’s Storm-Petrel”, H. c. ssp. nova, showing a relatively narrow white rump-band. (Isla Montaña Clara, Canary Islands; December 19, 2014.) © Stephen Menzie
“Grant’s Storm-Petrel”, H. c. ssp. nova, showing a relatively broad white rump-band. (Farol do Arnel, São Miguel, Azores; November 4, 2018.) © Alba Villarroya
References
Alderfer, J., and J.L. Dunn. 2014. National Geographic Complete Birds of North America (Second Edition). National Geographic Society, Washington, D.C.
BirdLife International. 2018. Hydrobates castro. The IUCN Red List of Threatened Species 2018: e.T132341128A132433305. https://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T132341128A132433305.en. (Accessed December 29, 2021.)
Bolton, M., A.L. Smith, A. L., E. Gómez-Díaz, V.L. Friesen, R. Medeiros, J. Bried, J.L. Roscales, and R.W. Furness. 2008. Monteiro’s Storm Petrel Oceanodroma monteiroi: a new species from the Azores. Ibis 150:717-727.
eBird. 2022. eBird: An online database of bird distribution and abundance. Cornell Lab of Ornithology, Ithaca, N.Y. http://www.ebird.org. (Accessed January 10, 2022.)
Flood, R.L., R.F. de Lima, M. Melo, P. Verbelen, and W.H. Wagstaff. 2019. What is known about the enigmatic Gulf of Guinea band-rumped storm petrels Hydrobates cf. castro? Bulletin of the British Ornithologists Club 139:173-186.
Galase, N.K. 2019. First confirmed Band-rumped Storm Petrel Oceanodroma castro colony in the Hawaiian Islands. Marine Ornithology 47:25-28.
Garcia-del-Rey, E. 2011. Field Guide to the Birds of Macaronesia: Azores, Madeira, Canary Islands, Cape Verde. Lynx Editions, Barcelona.
Garcia-del-Rey, E. 2018. Birds of the Canary Islands. Christopher Helm, London.
Harrison, P. 1983. Seabirds: An Identification Guide. Houghton Mifflin, Boston.
Howell, S.N.G. 2012. Petrels, Albatrosses & Storm-Petrels of North America. Princeton University Press.
Howell, S.N.G., and K. Zufelt. 2019. Oceanic Birds of the World. Princeton University Press.
Kirwan, G.M., A. Levesque, M. Oberle, and C.J. Sharpe. 2019. Birds of the West Indies. Lynx Edicions, Barcelona.
Onley, D., and P. Scofield. 2007. Albatrosses, Petrels & Shearwaters of the World. Princeton University Press.
Pratt, H.D., P.L. Bruner, and D.G. Berrett. 1987. A Field Guide to the Birds of Hawaii and the Tropical Pacific. Princeton University Press.
Pyle, R.L., and P. Pyle. 2017. The Birds of the Hawaiian Islands: Occurrence, History, Distribution, and Status. Version 2 (January 1, 2017). http://hbs.bishopmuseum.org/birds/rlp-monograph/. B.P. Bishop Museum, Honolulu, Hawaii.
Pyle, P., D.L. Webster, and R.W. Baird. 2016. White-rumped Dark Storm-petrels in Hawaiian Island Waters: The quandary of Leach’s vs. Band-rumped storm-petrels throughout the world. Birding 48:58-73.
Raffaele, H., J. Wiley, O. Garrido, A. Keith, and J. Raffaele. 1998. A Guide to the Birds of the West Indies. Princeton University Press.
Seabirding of Japan. 2021. Japanese Band-rumped Storm-Petrel. http://seabirding-japan.com/japanese-band-rumped-storm-petrel/. (Accessed December 17, 2021.)
Sibley, D.A. 2014. The Sibley Guide to Birds (Second Edition). Alfred A. Knopf. New York.
Svensson, L., K. Mullarney, and D. Zetterström. 2009. Birds of Europe (Second Edition). Princeton University Press.
Taylor, R.S., M. Bolton, A. Beard, T. Birt, P. Deane-Coe, A.F. Raine, J. González-Solís, S.C. Lougheed, and V.L. Friesen. 2019. Cryptic species and independent origins of allochronic populations within a seabird species complex (Hydrobates spp.). Molecular Phylogenetics and Evolution 139:106552.
The Sound Approach. 2019. Cape Verde Storm-Petrel, Oceanodroma jabejabe. https://soundapproach.co.uk/species/cape-verde-storm-petrel/.
The Sound Approach. 2019. Grant’s Storm-Petrel, Oceanodroma [castro]. https://soundapproach.co.uk/species/grants-storm-petrel/.
The Sound Approach. 2019. Madeiran Storm-Petrel, Oceanodroma castro. https://soundapproach.co.uk/species/madeiran-band-rumped-storm-petrel/.
The Sound Approach. 2019. Monteiro’s Storm-Petrel, Oceanodroma monteiroi. https://soundapproach.co.uk/species/monteiros-storm-petrel/:
Xeno-Canto. 2021. Band-rumped Storm Petrel – Oceanodroma castro. https://xeno-canto.org/species/Oceanodroma-castro. (Accessed January 10, 2022.)