Time’s virtually up for the Scopoli’s (Calonectris diomedea) and Cory’s (Calonectris borealis) Shearwaters to go away for waters within the South Atlantic the place they’ll spend the winter. These two sister species had been thought-about a single species till pretty lately once they had been separated as full species primarily based on genetic proof. Broadly talking, Scopoli’s Shearwaters breed within the Mediterranean Sea and Cory’s Shearwaters at equal latitudes on the Atlantic Ocean.
Residing in Gibraltar, with its well-known Strait on my doorstep, I’ve grow to be within the distribution of the 2 species right here, simply within the zone of overlap. For a few years I’ve been going out to see to look at the spectacle of those shearwaters feeding on the migrating flying fish in late September and October. I had assumed that these had been largely Cory’s Shearwaters, coming in from the Atlantic, however wanting again at a few of my pictures I started to marvel.
So, I went out into the Strait this month and began to take as many pictures as I might. I’m nonetheless analysing the photographs however I’d say that 70% of the birds on the market had been Scopoli’s and 30% had been Cory’s. Is that this typical or does the proportion range from each day or at totally different occasions of the summer season and autumn? I can’t reply that proper now however I’m going to attempt subsequent yr. Photographing them, even distant ones, goes to be the best way of unravelling the thriller. We’re getting to grasp how one can separate the 2 species within the area and a number of other good papers have been printed lately, together with one within the newest problem of British Birds. One give away ifs the underside sample of the primaries. In Cory’s the primaries are darkish and type a straight line on the base. In Scopoli’s, the white extends into the primaries. There are different options. For me, Scopoli’s are extra gracile in construct than Cory’s, the beak being slighter. Then there may be the flight. When flapping, Scopoli’s seem to beat their wings extra ceaselessly, suggestive of a smaller chook altogether.
The Mediterranean-Atlantic separation is probably not that clear. I’ve lately come throughout Scopoli’s Shearwaters within the Gulf of Cadiz, on the Atlantic, amongst rafts of Cory’s. Current reviews are additionally displaying Scopoli’s even amongst Cory’s off the Isles of Scilly!
There may be one factor I’m now watching out for. This week and the following will see the exodus of Scopoli’s Shearwaters out of the Mediterranean. They journey in giant, tight, flocks, with a willpower that claims migration throughout. After that I must wait till subsequent February when they’ll return from their wintering grounds.
However it gained’t be the top of shearwaters within the Strait. Already, the smaller Balearic Shearwaters (Puffinus mauretanicus) are getting back from the Atlantic moulting grounds. They now begin visiting the breeding colonies within the western Mediterranean and can begin breeding early within the yr. By Could, they are going to be heading again out in the direction of the Atlantic. I’m fortunate to have shearwaters right here all yr!
All pictures illustrating this text had been taken off Gibraltar on the identical day.
