Storm petrels, or "Mother Carey's Chickens", as they
have long been called by sailors, are the smallest of the Procellariiformes.
The name "Petrel" is thought to be derived from St.
Peter, because their habit of not quite landing in the water,
but dipping their feet in and fluttering over the surface while
they feed on plankton, makes them seem as though they are walking
on water. World-wide, there are eight genera of storm petrels,
containing about 20 species. These eight genera are divided into
two main groups, one inhabiting the northern hemisphere, and the
other the southern, with some overlap in the tropics. In the Galapagos,
there are three resident species:
- White-Vented (Elliot's) Storm Petrel (Oceanites
- Band-rumped (Madeiran Storm Petrel (Oceanodroma
- Wedge-Rumped (Galapagos) Storm Petrel (Oceanodroma
Of the three, Oceanites is a southern form
while Oceanodroma is a northern form. Both the white-vented
storm petrel and the wedge-rumped storm petrel are endemic Galapagos
subspecies. Other species of storm petrels have occasionally been
reported as vagrants.
Storm petrels are not often easy to identify because
of their very small size (6-8 inches), rapid movements, and generally
great distances from the observer. The white-vented storm petrel,
which is the species in the photographs to the left, are the most
commonly sighted inshore species. It is part of the southern grouping
of genera and, typical to that group, it has very long legs which
project behind the tail. In Galapagos, it is the only storm petrel
with this feature. All three Galapagos storm petrels have a white
patch on their rump. The narrowest is the band-rumped while the
largest is the wedge-rumped, in which the patch is strongly triangular
and the point extends deeply into the tail.In the White-vented
storm petrel, the band wraps around the belly, as can be best
seen in the middle photograph. Also a distinguishing feature of
the white-vented storm petrel is its squared-off tail. All three
storm petrels, like storm petrels everywhere have their nostrils
fused into a single tube on the top of their beak.
Despite the fact that the white-vented storm petrel is a resident,
endemic subspecies, its breeding sites have never been found.
Autopsies of dead birds suggest that they lay their eggs from
April to September. The other two species, both Oceanodroma,
have well established breeding areas. One well known site is on
the cliffs above Prince Philip's Steps on Genovesa.
There, the birds nest in the numerous lava tubes and cracks that
riddle the ground. The birds fly rapidly back and forth, seeming
more like a swarm of insects than a flock of birds. The wedge-rumped
storm petrel is the only one to visit its breeding site during
the day, feeding by night. Thus, any day-time siting of a feeding
storm petrel will most likely not be the wedge-rumped. The wedge-rumped
petrel breeds from April to October, laying one egg that is incubated
by both parents. The band-rumped petrel likewise lays a single
egg, but breeds in two groups, one from February to October, and
the other from October to May. Like other storm petrels, and unlike
its neighbor, the wedge-rumped, it feeds during the day, usually
farther out to sea than the white-vented storm petrel, and returns
to its nest at night.