Seabird 2000
Leach's Storm-petrel
Oceanodroma leucorhoa
The following was adapted from
original text by P. Ian Mitchell in
Seabird Populations of Britain and Ireland (with
permission from A&C Black, London).
Leach's Storm-petrel is a truly oceanic species, only
returning to remote island colonies under hours of darkness. It
ranges widely in both the Atlantic and Pacific Oceans. In the east
Atlantic, breeding colonies of Leach's Storm-petrels are confined
to a few islands off the coasts of Iceland, the Faeroes and Norway,
as well as on just eight remote islands and archipelagos situated
along the Atlantic Frontier of Britain and Ireland. Obtaining
estimates of breeding numbers has been virtually impossible, due to
the nocturnal and subterranean breeding habits of Leach's
Storm-petrels and accessing the remote colonies during the hours of
darkness is often difficult and dangerous.
Seabird 2000 used a method called tape playback to survey
apparently occupied sites (AOS) of breeding Leach's Storm-petrels.
The method involves playing calls of Leach's Storm-petrels to
elicit a response from adults hidden in burrows during the day
whilst incubating. Unfortunately not all Leach's Storm-petrels
present at a colony will respond to the taped calls, thus counts of
responses will underestimate the number of AOSs and have to be
adjusted by a response rate measured at the colony.
In Britain and Ireland, 94% of Leach's Storm-petrels breed on
four islands in the St Kilda archipelago, with the remainder on the
Flannan Isles, plus three other islands in the Western Isles, two
islands in Shetland and just one colony in Ireland. Colonisation of
islands by Leach's Storm-petrels is dependant on the absence of
rats (and other mammalian predators) and on proximity to their
feeding grounds. Leach's Storm-petrels feed on macro-zooplankton
(e.g. myctophids, amphipods, euphausiids) and, in the east Atlantic
(during the breeding season), are confined to feeding in areas
beyond the continental shelf break (deeper than 200m), and are
concentrated over the continental slope (200m-1000m) and in deeper
water (1000m – >2000m). All British and Irish Leach's
Storm-petrel colonies are within 37-67km of the shelf break and
65-119km from the bottom of the continental slope. It is unknown
whether or not any changes in the abundance of their planktonic
prey have affected breeding populations of Leach's Storm-petrels,
but some colonies appear to be under threat from predation from
mink, feral/domestic cats and Great Skuas.