I am away this week, so I am taking the opportunity to invite colleagues to tell you about some of our International Research.  In today's guest blog, Steffen Oppel goes cat tracking to solve the mystery of disappearing shearwater chicks.

I just returned from a tiny speck of land in the North Atlantic - the island of Corvo, which belongs to the Azores archipelago.  It is roughly half-way between Europe and North America, a single volcanic cone rising to 750m above sea level.  The island used to be a seabird haven - millions of shearwaters and storm petrels nested on the 600m cliffs, enjoying safety from land mammals and the rich food sources of the cold temperate waters surrounding the island.  Then, about 500 years ago, Portuguese sailors discovered the island, and today it's a shadow of its former self.

Corvo (Steffen Oppel)

Like many other islands around the world, most of the original vegetation on Corvo has been replaced by invasive species.  Mammals were introduced, and wreaked havoc.  Goats and sheep stripped the island of native vegetation, and rats and cats ate seabirds and their young.  Some seabird species may have completely disappeared, but others still breed in reasonable numbers, so there is hope that the island can become a seabird haven again if threats can be identified and eliminated.

 The local BirdLife partner SPEA has been working with the 400 inhabitants on Corvo to restore the island to former glory.  The first task was to find out what challenges the seabirds that are still breeding on Corvo face.  Together with a PhD student, Sandra Hervias, we analysed 3 years of nest monitoring data of Cory's shearwater - the largest species of seabird nesting on Corvo.  The results were very clear - as soon as the chicks hatch in early July, the shearwater colonies are raided by cats. Only about 40% of chicks survive, the vast majority killed by cats and, to a lesser extent, rats.  Removing cats and rats from the island would be the best thing to do - but of course people love their pet cats, and removing all cats from the island would be deeply unpopular.

Is this the culprit? (Steffen Oppel)

We then used small GPS loggers to find out where the cats from the village go at night - there is only one village on Corvo!  These nifty little tools can be attached to a cat collar because they weigh only 20g and won't bother the cat.  The position is then recorded every 10 minutes for over a week, so we know exactly where the little tigers prowl around.  Surprisingly, most of the cats were lazy couch potatoes, rarely venturing more than a few hundred metres from home.  But there was one cat that set out on a mission one night, walked almost 15km in just 5 hours, and visited several of our shearwater colonies in a row!  Clearly that cat had developed a taste for shearwater chicks, and knew exactly where to find them.  We have only tracked 25 cats so far, so a bit more work is required, but it seems that a small number of specialised individuals may be responsible for the damage done to seabirds on Corvo.  The question then is, can we 'arrest' known culprit cats and prevent them from roaming the island and terrorising birds?

Cat tracks on Corvo (Steffen Oppel)

We will track more cats over the course of 2012 to get a better understanding of their movements - and to unmask the killers.

I am be back next week.  If you would like to follow these international projects and many more, why not sign up to the Saving Species, Rainforests and Saving Special Places blogs?  We're Stepping Up For Nature in amazing places around the world.

  • This is a similar result to the work on crow and raven predators that I have seen when predating wader nests in the uplands; ie a few specialists do much of the damage. This story is of course an insight into evolution, this is how it happens;individualism. its positive for that cat ie fitter and stronger? and potentially very negative for the shearwaters?