Bird night attacks may be unique
Steven McKenzie BBC Scotland News, Highlands and Islands reporter
Last Updated: Monday, 5 November 2007, 00:42 GMT
Incidents of a seabird preying on colonies of another species at night
may be unique to a remote islands archipelago.
Ecologist Will Miles said initial research of great skua preying on
Leach's petrel on St Kilda found the behaviour was unlikely to be
The National Trust for Scotland (NTS) has been recording "alarming"
falls in the smaller petrels on the islands.
Mr Miles and fellow researchers used night vision gear to observe the
NTS said the Leach's petrel colony on St Kilda, which it owns, is the
largest in Europe and numbers about 40,000 pairs.
Researchers from Glasgow University have been investigating suggestions
that great skua, or bonxie, may be eating up to 14,000 petrels every
The research on Hirta, St Kilda, will run until 2009.
Results of this year's work are still being analysed, however, Mr Miles
revealed some intriguing insights into the bonxies' behaviour.
He said: "The skuas are highly active on the petrel colonies at night
and catch petrels in a variety of ways - both on the ground and in the
"Nocturnal foraging by great skuas is thought to be quite a rare
"At least, it has not been widely reported from the most intensively
studied skua colonies on Shetland or from elsewhere across the species'
"The situation on Kilda seems rather unique in this respect."
Why the bonxie prey on petrels may be down to a combination of factors.
Great skua feed on fish, carrion and other birds. The RSPB give them
green status, meaning there is no identified threat to its population
The starling-sized Leach's petrel lives on crustaceans, molluscs and
Leach's petrel have amber status - meaning that they have suffered a
historical decline but have recovered
They include limited other food sources, competition between the skuas
and when the birds nest close to petrel colonies.
Mr Miles said: "Skuas are highly opportunistic predators and some
individuals seem to develop a taste for certain prey types.
"One possibility may be that on Kilda the petrels are a relatively
abundant prey type, a few individual skuas have exploited this
situation opportunistically and their behaviour has been copied by
others looking for an easy meal."
After assessing the safety of vantage points, the researchers spent
nights close to high cliffs, steep slopes and scree boulder fields.
Mr Miles said: "Once on-site, we then stayed put in one watching
position for the hours of darkness and just observed the bird activity."
The vigils were often to the backdrop of the sound of puffins, manx
shearwaters and European storm petrels.
Mr Miles said: "The call of the shearwaters is particularly evocative
and bizarre - sometimes likened to a chicken with asthma. It is rather
a wheezy, wailing sort of call."
Mr Miles admitted it could be hard to be an impartial observer.
He said: "Yes, Leach's petrels seem tiny and elegant seabirds when
compared with bonxies, so of course it can be difficult to watch a
petrel get eaten without feeling some kind of regret.
"Predation is a normal occurrence in nature though, even if rarely
Data gathered by researchers will be used to help guide conservation
efforts for both species.
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