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 have been thought of a single species till pretty just lately once they have been separated as full species based mostly 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 turn out 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 watch the spectacle of those shearwaters feeding on the migrating flying fish in late September and October. I had assumed that these have 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 may. I’m nonetheless analysing the photographs however I’d say that 70% of the birds on the market have been Scopoli’s and 30% have been Cory’s. Is that this typical or does the proportion range from day after day or at totally different occasions of the summer season and autumn? I can not reply that proper now however I’m going to strive subsequent yr. Photographing them, even distant ones, goes to be the best way of unravelling the thriller. We’re getting to grasp methods to separate the 2 species within the discipline and a number of other good papers have been printed just lately, together with one within the newest concern 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 regularly, suggestive of a smaller chook altogether.
The Mediterranean-Atlantic separation might not be that clear. I’ve just lately come throughout Scopoli’s Shearwaters within the Gulf of Cadiz, on the Atlantic, amongst rafts of Cory’s. Latest reviews are additionally exhibiting Scopoli’s even amongst Cory’s off the Isles of Scilly!
There’s one factor I’m now watching out for. This week and the subsequent will see the exodus of Scopoli’s Shearwaters out of the Mediterranean. They journey in massive, 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.
Nevertheless it received’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 direction of the Atlantic. I’m fortunate to have shearwaters right here all yr!
All pictures illustrating this text have been taken off Gibraltar on the identical day.