Monday, September 20, 2010

September feeding frenzies in the Strait of Gibraltar

September is the month of the flying fish in the Strait of Gibraltar. If they turn up in good numbers they unleash a chain of spectacular events as all kinds of predators converge on this rich food resource. It is the dolphins that get things moving by chasing the fish near the surface where seabirds also get a chance to have a go at them. Yesterday morning was a calm easterly, ideal for a feeding frenzy. It was also the end of the Calpe Conference on the evolution of bird migration, so what better time than to go out on a boat and see what was happening.
Rafts of Cory's Shearwaters Calonectris diomedea at the entrance to the Bay of Gibraltar soon have a hint that the morning would be a good one...
Once round Europa Point and into the entrance to the Mediterranean, a wonderful spectacle unfolded which combined dolphins, breeding shearwaters and migratory seabirds. A migrating Loggerhead Turtle Caretta caretta was a promising sign...
Soon we found the pods of Common Dolphins Delphinus delphis that were frantically chasing the flying fish...
Cory's Shearwaters flew over the pods keeping an eye for shoals of fish
Several thousand Cory's Shearwaters were about, having flown down the Mediterranean coast some 400 kilometres to feed in these rich waters where the Atlantic meets the Mediterranean. These are daily feeding movements as they have hungry chicks in their nests.

As soon as the dolphins have got going, the shearwaters get busy catching the fish that try to escape by gliding...
...and competition is severe among the shearwaters
but the shearwaters do not have it all to themselves as gulls try and steal the tasty meals...

but gulls are insignificant compared to the big bullies that, passing by on migration, get attracted by the concentrations  - Arctic Stercorarius parasiticus and Great Catharacta skua (below) skuas are more formidable opponents...
other migrants also joined in the fun. Among these were juvenile Gannets Morus bassanus, just arrived ftom the North Atlantic.

Black Chlidonias nigra, Common Sterna hirundo and Sandwich Thalasseus sandvicensis terns moving towards the Atlantic wintering grounds also got drawn in...

as were other locally breeding shearwaters - the smaller and browner Balearic Shearwaters Puffinus mauretanicus

but the day belonged to the larger shearwaters, adding plunge-diving to their hunting techniques until the food was gone...

My thanks to Tony and Angie Watkins of Dive Charters for taking us out on their boat

Monday, September 6, 2010

Honey Buzzards - the great travellers

European Honey Buzzards Pernis apivorus are amongst the most beautiful of raptors and they are great travellers
This species breeds in the western and central Palaearctic and is replaced further east by the Oriental Honey Buzzard P. ptilyorhynchus.
There is a third species, the ancestral form, which lives across many islands of south-east Asia - in Sulawesi and the Philippines - where the Oriental Honey Buzzard's range, which has populations across South and South East Asia, ends. It is the Barred Honey Buzzard P. celebensis. These tropical Honey Buzzards are sedentary but the Palaearctic populations of Oriental and all European Honey Buzzards migrate. Their specialised diet of bees and their larvae prevents them being resident away from the tropics.
Hundreds of thousands of European Honey Buzzards arrive in Europe and western Asia to breed in late April and May. They have a short breeding season, capitalising on the abundance of their favourite prey, and leave as soon as breeding is over. They cross the major flyways, avoiding long sea crossings, but are better able to cope with flying over the sea than most raptors and they even get across into Africa via Malta.
Even so flying over the sea can be hazardous.

The Honey Buzzards that are now peaking over the Strait of Gibraltar, with numbers exceeding 11 thousand on good days, are coming from western Europe, Scandinavia and western Russia. Many have crossed from Scandinavia into continental Europe at Falsterbo and the journey to Gibraltar takes them about a week.
These birds are heading for the forests of tropical West Africa, so they still have the big hurdle of the Sahara Desert - 1500 kilometres of sand without chance of eating or drinking - before arriving home.
The Honey Buzzard is typified by a variable plumage. Most birds are of the typically barred phase (above) but others are chocolate brown (below).
and others white (below).
I will keep an eye out for these migrants in the next few days and report back on their progress, along with that of other raptors...
thermal of Honey Buzzards on the move (above). These flocks may number in the thousands.