a web page by Don Roberson |
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STORM-PETRELS Hydrobatidae |
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Wilson's Storm-Petrel breeds on southern hemisphere islets and disperses north widely thereafter. The are huge numbers in the Atlantic; some believe the species to be among the most abundant birds in the world in sheer numbers. Many fewer reach the north Pacific, but they are annual in our autumn on Monterey Bay in California. |
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The storm-petrel family has two subfamilies: the Oceanitinae, composed of southern hemisphere species which are characterized by long legs (like Wilson's Storm-Petrel), and the Hydrobatinae, composed of northern hemisphere or tropical species which typically have much shorter legs and often have forked tails. Christidis & Boles (2008) elevated these two subfamilies to full family status, relying on molecular evidence published by Penhallurick & Wink (2004). This has not been widely accepted by other authorities, but it does appear the two subfamilies are very ancient lineages. |
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| An impressive concentration of storm-petrels occurs in Monterey Bay, California, annually. Each fall nearly the entire world's population of Ashy Storm-Petrels gather in day roosts over the north rim of a huge underwater canyon in Monterey Bay. Depending on oceanic conditions, these will be joined by hundreds to thousands of Black Storm-Petrels from the south, and the occasional Least or Wilson's or Fork-tailed Storm-Petrel (vagrant Wedge-rumpeds have even occurred). The montage below combines photos from 3 photographs (Les Chibana, Jeff Poklen, Don Roberson) in two years (2004, 2006) to show a bit of the experience. The upper and lower tiers show the flock, mostly Ashy, on the water or just taking off. In Jeff Poklen's middle left shot, one can compare a few larger Black Storm-Petrels among the Ashy Storm-Petrels and there is a mystery bird near the center that could be a Least. Les Chibana's shot of a definite Least Storm-Petrel is middle right (and much enlarged compared the rest). | |||
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Recent genetic and breeding phenology evidence suggests that there may be four (or more?) distinctive populations of Band-rumped Storm-Petrel in the tropical Atlantic Ocean (Bolton et al. 2008, summarized in Robb et al. 2008, Bennett 2009). Further, populations in the Pacific are even more distinctive (Friesen et al. 2007, Bolton 2007). It is possible that birds currently lumped as "Band-rumped Storm-Petrel" Oceanodroma castro should be assigned to somewhere between two (Atlantic vs. Pacific) to six or more species (four in Atlantic, two more in Pacific). In the Atlantic there are summer breeding birds on the Canary Is., Madeiran Is., and Selvagens (nominate castro) and summer breeders in the Azores (already proposed as O. monteiroi Monteiro's Storm-petrel; Bolton et al. 2008), and then there are winter breeding populations on the Azores, Canaries, and Madeiran islands (not yet formally named but informally proposed as "Grant's Storm-Petrel" in Robb et al. 2008; the photo above right is presumed to be from this population), and a year-round breeder on the Cape Verde Is. (jabejabe; can breed much of year but most nest in winter; Robb et al. 2008). In addition, there is now evidence of summer and winter breeding populations on St. Helena I. in the south Atlantic (Bennett et al. 2009); there are also summer and winter breeders in the Galapagos (Friesen et al. 2007). Band-rumped is not the only storm-petrel to have summer and winter breeding populations on the same island. This phenomena also occurs in populations of Leach's Storm-Petrel on Guadalupe I. off western Mexico; Ainley (1980, 1983). |
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 Storm-Petrels
have incredible powers of smell and therefore can locate potential
items to scavenge from miles away. One Band-rumped in the eastern
tropical Pacific followed in our ship's wake for an hour, quite
possibly attracted to odors emanated from the kitchen for the large
research ship, or oily wastes dumped overboard. On this same research
cruise we came upon a large dead baleen whale in tropical waters about
400 miles SW of the tip of Baja California. The carcass of this dead
whale was surrounded by hundreds of Wedge-rumped Storm-Petrel (left). By the time we got close, many of the birds had flown but there are at least four in this shot. |
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There are some other wonderful storm-petrels in the world, including the Polynesian Storm-Petrel Nesofregetta fulginosa that has this astonishing flight pattern, seeming to skip of the water erratically each time it glides down, careening from point-to-point like the mechanically ball in the old "Pong" video game. Storm-Petrels breed on remote islands, islets, or on certain desert mountains in South America free of land predators. Most come ashore to breeding sites after dark to avoid predation by gulls or other large seabirds. On the Farallon Islands off San Francisco, California, for example, where I have spent a couple weeks helping research efforts, the air is alive with the sounds of returning Ashy and Leach's Storm-Petrels after dark in the summer. Over 90% of the world's Ashy Storm-Petrels nest on the Farallones. You can now enjoy the cacophony of sounds made by some Atlantic storm-petrels on the CDs that come with Robb et al. (2008). |
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Photos: The shots of Wilson's Storm-Petrel Oceanites oceanicus were off Hatteras, North Carolina, on 14 June 2009. The Leach's Storm-Petrel Oceanodroma leucorhoa came aboard the research vessel McArthur at 2°17'N, 116°59'W, on 30 Nov 1989. The Fork-tailed Storm-Petrel Oceanodroma furcata was photographed from Monterey's commercial wharf on 25 Aug 1983. The flocks of Ashy & Black Storm-Petrels O. homochroa & O. melania were on Monterey Bay, California, on 19 Sep 2004 (top tier of montage © Les Chibana, middle left tier © Jeff Poklen, and 30 Sep 2006, bottom tier D. Roberson) while the isolated Least Storm-Petrel Halocyptena microsoma was photographed by Les Chibana on 5 Sep 2004. The Band-rumped Storm-Petrel O. castro was at about 19°N, 115°W, on 2 Aug 1979. The scavenging Wedge-rumped Storm-Petrels O. tethys were surrounding the whale carcass at 21°04'N, 87°53'W, on 1 Aug 1989; our best guess at the whale species involved was a Fin or a Bryde's Whale. The Ringed Storm-Petrel O. hornbyi was west of northern Peru at 3°S, 82°W, on 29 Sep 1989. All photos © Don Roberson, except those attributed to © Les Chibana and © Jeff Poklen, and used with permission; all rights reserved. Bibliographic essay
Literature cited:
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Storm-petrels
are small aerial seabirds found in all oceans of the world. Some say
the name "petrel" comes from a French version of St. Peter who, in
biblical traditions, walked on the water. The "storm" part of their
name refers to the fact they are only found on land during very strong
storms. Indeed, the thin legs of storm-petrels cannot sustain their
weight for more than a few steps — they avoid land except to come
ashore, usually at night, to breed in burrows, caves, or crevices.
Watching Wilson's Storm-Petrel patter over the water
(above & left), one can well imagine the tales that were spun by
ancient mariners. Some seafarers of old called them "Mother Carey's
chickens," in reference to the Virgin Mary (Mater cara) to whom the protection of sailors was commended.
Storm-petrels,
like other members of the order Procellariiformes, have specially
modified "tubes" atop their bills. This special organ, which you can
see in this in-hand photo of a Leach's Storm-Petrel
(right). This allows them to drink salt water and then dispose of the
salt. One can sometimes see drops of concentrated sale being "sneezed"
out of these tubes.
Some
storm-petrels are highly migratory, spending the summer month in rich
cold waters far north or far south, and then moving toward the
subtropics in the winter months. One of these is the lovely Fork-tailed Storm-Petrel
(left) which breeds on tiny islets from Japan and Alaska south to
northern California, and then disperses widely over deep oceanic waters
in the non-breeding season. Where I live on Monterey Bay, California,
this species is almost always far offshore. Occasionally, strong NW
gales in spring or fall will force hundreds into Monterey Bay itself,
and for a few days thereafter birds can sometimes be seen from shore. I
took this photo from Monterey's commercial wharf during one such
incursion. The Fork-tails blown inshore try to get back offshore as
soon as possible. Local Western Gulls find them to be easy prey, and
storm-petrels inshore don't last long.
About
half of the storm-petrel species are tropical or subtropical, staying
within warm waters but wandering widely as food can be patchy and hard
to find. A set of storm-petrels of deep offshore warm waters is
currently delimited under the name Band-rumped Storm-Petrel
(right). Its basic pattern — black bird with a white rump band — is a
feature shared with 8 other species. The bands vary is size and extent,
but identification of these birds can be difficult. Flight styles and
behaviors are important; see Crossin (1974), Boswell (1979), Brown
(1980), Marsh (1980), Naveen (1981-1982), and Harrison (1983a) for
starting points.
