|proudly sponsored by Oryx||
Birds in Spain
Text & photos by Ricard Gutiérrez
Recent sightings of Calonectris shearwaters in the Atlantic have raised questions about the variability of the white underwing pattern described as diagnostic for diomedea in the aim of telling it from the Atlantic and more numerous form borealis (see Gutiérrez 1988 for the first discussion on the subject and Martin Reid's webpage and Dick Newell's webpage for further photos and discussion on the subject).
The Gutiérrez (1988) paper which set a number of characters but basically underwing pattern as a good form to tell both forms, as well as the previous McGeehan,A. & Gutiérrez,R.1998, Great Dilemmas. Birdwatch, 73:32-36 were largely based in personal observations from some of the Canary Islands and Azores islands too regarding borealis and extensive material from the Mediterranean, off Catalonia, NE Spain. The 1998 criteria (such as similar criteria recently published regarding separation at sea of Puffinus mauretanicus, yelkouan and puffinus, Gutiérrez,R.2004, Birding World 17:111-122) are based at least from the Spanish perspective in the few things we know on these 'hard-to-work' birds. All methods details are written in the respective papers.
Some further advances in the knowledge of both forms have been achieved in the last years. borealis forms a cline in which the Azores birds are the larger (and to me easier to tell birds from diomedea) then coming the Madeiran birds and after those the Canary Islands birds showing all differences in measurements (see e.g. Massa & Lo Valvo 1986). Although some colonies have been largely studied (e.g. Columbretes in Spain or Selvagem in Portugal), others -e.g. Canary Islands (until 2004: this year some studies are being held) are largely unknown.
Now it is known that both forms share wintering grounds (Camphuysen & van Der Meer 2001). This paper successfully tested the 1998 Dutch Birding criteria.
Of more interest to birders is that it has been proven in the last years that there is some exchange of birds between colonies of borealis (at least proven from Selvagem islands, between Madeira and Canary Islands) and the Mediterreanean colonies (e.g. Martínez-Abraín et al 2001)
Nobody knows how the 'hybrid' birds between diomedea and borealis do look like. And it is published that up to 4-19 birds can be exchanged per generation. So it may well be that there is a (has to be small if figures are right) number of birds over there showing intermediate characters from those I set from the say two extremes of the cline: Azores and Mediterranean. However, it is yet to be fixed which this proportion might be because hybridisation does not seem to be a widespread behaviour(or at least that is what we know for the moment).
So it may well be that some birds are unidentifiable at sea, at least from a single photo. Anyway, no apparent borealis have been recorded off NE Spain coast in the last years (last four years with regular monthly seawatches). As an example, some photos are included below depicting different birds in august 2004 off Garraf, Barcelona. And I look forward to include in the future more pictures to complete this series with birds from Madeira, Azores and the Canary islands.
Given there is a sort of cline between Calonectris colonies regarding size and some bare parts proportions, would the underwing pattern show any variation in the white extent? and up to which?. It seems clear that both extremes are safe-telling but some populations and birding areas are poorly documented. And a possible, albeit apparently not seen at sea, intra-colony variation in diomedea perhaps might be possible given the borealis gene flow exposed above.
Said that, I'm beggining with the collaboration of colleagues from Canary Islands for the moment, to study any corpse or alive bird we can to measure the variation of the extent of white and black in the outermost wing primaries, those that explain the white pattern to see if the already stated pattern can be 'measured'. Although a long-term study,hopefully it will bring us more light into the variation of these tubenoses.
Generalitat de Catalunya through the Fishing Inspecting Unit of DARP made possible the Garraf and Llobregat delta offshore transects which were useful for picture-taking purposes. The Servei de Protecció de la Fauna, flora i animals de companyia allowed the inspection of two corpses collected in Catalonia. To all those interested in the subject whose interest is putting forward the knowledge we have on these tubenoses.
All photos © Ricard Gutiérrez, scanned from original slides taken with Nikon F604 and 80-300 mm Nikkor teleobjective on board Xot vessel off Garraf coast, Barcelona.
Underwing pattern in Scopoli's Shearwaters Calonecris diomedea diomedea off NE Spain in Summer 2004
Designed to be seen in 800x600
resolution with Java enabled browsers.