Band-rumped Storm-petrel (Oceanodroma castro)

Taxonomy

Also known as Madeiran Storm-petrel or Harcourt's Storm-petrel

Generally treated as monotypic although this might change in the near future. Several potential subspecies have been described based on differences in bill structure, wing length and the amount of white on the rump (Austin, 1952). More recent work by Luis Monteiro and colleagues on the Azores suggests the existence of two distinct breeding populations. Termed cool- and hot-season breeders, the two populations apparantly occupy the same nesting areas but breed at different times of the year (reviewed in Sangster, 1999). In addition to the seasonal segregation, Monteiro and coworkers report statistically significant morphometric differences between the two population (Monteiro and Furness, 1998). These differences are greater that those between corresponding hot-season populations on the Azores and Madiera. Monteiro and Furness (1998) mention that preliminary mitochondrial DNA sequence analysis is also supportive of genetic isolation.
 

Identification

Intermediate in size between Leach's Storm-petrel and Wilson's Storm-petrel. Differs from Leach's Storm-petrel in having broader and slightly shorter wings with more rounded tips. Wing tends to be held out straight rather than angled as in Leach's Storm-petrel. Slightly darker pale carpal bar running across greater wingcoverts and a more extensive white 'rump' patch that extends onto lateral undertail coverts. More square cut than Leach's, although this may vary with molt. The tail is less deeply forked than on Leach's Storm-petrel. Juveniles are like adults but show paler carpal bar.

Flight style is extremely useful in separation from both Leach's (erratic, resembling the North American Common Nighthawk) and more fluttery flight of Wilson's Storm-petrel. Uses dynamic soaring more than the other two species. Typically 'zigzags' with periods of rapid, fairly deep wing beats followed by shearwater-like glides on bowed wings. Can make rapid turns, doubling back on itself and is hard to chase with a boat. Will occasionally patter, but not nearly as much as Wilson's. Sometimes feeds whilst swimming on surface. Separation from Wilson's relatively difficult and benefits from comparative experience. Click here to read a description by Paul Buckley of the differences in wing posture between Band-rumped and Wilson's Storm-petrels. Unlike Wilson's Storm-petrel, the feet do not project noticably beyond tail in direct flight. Can be separated from the even smaller European Storm-petrel by the same criteria as Wilson's Storm-petrel. European Storm-petrel is even more fluttering than Wilson's.

David Sibley has discussed the problems of using molt status in identifying storm-petrels in the North Atlantic/Gulf of Mexico.

There is currently no data on field separation of the two seasonal populations nesting in the Azores, however these birds have subtle differences in body proportions and might therefore be separable. Hot-season birds are smaller than cool-season birds and yet have longer wings, relative to body size, and longer and deeper forked tails (Monteiro and Furness1998).
 

Where and When

A rather cosmopolitan breeder found in the North Atlantic, South Atlantic and Pacific Ocean (islets off Portugal, the Canary Islands, Madiera, Salvage Islands, Azores, Cape Verde Islands, Ascension, St Helena, off Japan, in Hawaii and the Galapagos). Nests in crevices in rock piles and stone walls or burrows in soft earth.

The first proof of breeding in the Azores was obtained in the early 1990s by Luís Monteiro and coworkers. There are three known breeding colonies, all on small, rat-free islands. One is situated on Vila (near Santa Maria), the others 300 km to the north-west on Baixo and Praia (both near Graciosa).

Highly pelagic away from breeding grounds. Seen regularly in deep Gulf Stream water off North Carolina, particularly in the summer months.
 

Literature

Austin, O. L. (1952) Notes on some petrels of the north Pacific. Bull. Mus. Comp. Zool. 107: 391-407.

Case, E. G. (1998) Evidence of Band-rumped Storm Petrels (Oceanodroma castro) off the Alabama Coast. Alabama Birdlife 43(2): 4-9.

Friesen, VL., Lodha, V., Monteiro, LR and Furness, RW (1998) Evidence for sympatric speciation in the Band-rumped Storm-petrel Oceanodroma castro. Ostrich 69: 400-401.

McCaskie, G. (1990) First record of the Band-rumped Storm-Petrel in California. Western Birds 21:65-68.

Mlodinow, S. G. and O'Brien, M. (1996) America's 100 Most Wanted Birds: Finding the lower 48's rarest species. Falcon Press, Helena and Billings, Montana.

Monteiro, L.R. and Furness, R.W. (1998) Speciation through temporal segregation of Madeiran Storm-petrel (Oceanodroma castro) populations in the Azores? Phil. Trans. R. Soc London B 353:945-953.

Sangster G. (1999) Cryptic species of storm-petrels in the Azores? Dutch Birding 21: 101-106.



Copyright © 2002 All rights reserved. Angus Wilson
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