Wednesday, September 28, 2011

September Feeding Frenzy in the Strait of Gibraltar

This is the time of year when flying fish are passing through the Strait of Gibraltar. They attract many predators that chase them and catch them below or above the surface of the water. These concentrations provide a unique opportunity to see large concentrations of marine predators. Last Sunday we were able to experience this amazing event. See our blog of 20 September, 2010, for a similar event.

Last year we found them in the Mediterranean, east of Gibraltar, but this time they were in the Strait within view of the mist-covered and imposing Rock. Below are some scenes from this magical event...

Leading the underwater action were Common and Striped Dolphins

On the surface, the main predator was Cory's Shearwater

They wait patiently, and peacefully, in rafts until, that is, the dolphins bring the fish to the surface. Then the squabbling commences!

Just like the smaller vultures at a carcass, the Balearic Shearwaters (below) operate on the fringe as they wait for scraps

Gannets arriving from the Atlantic to winter also join in. Most are juveniles or immatures. There are very few adults right now, most will arrive in October.

These past weeks have been very busy for us in the field, so we need to catch up with a number of stories. So keep visiting our blog!

Sunday, September 4, 2011

The Day of the Honey Buzzard

Late August and early September mark one of the most incredible and impressive of bird migration spectacles - the passage south of the Honey Buzzard Pernis apivorus across the Strait of Gibraltar

Tens of thousands of Honey Buzzards migrate south in the space of a week or so. They come in tight flocks which adds to the air of spectacle. These birds are coming from Scandinavia, western Russia and Western Europe. They are bound for the tropical forests of West Africa.

Their plumage is very variable and we can identify three main plumage types or phases - they are linked to each other by intermediate patterns. The most common phase is the intermediate or barred (above)

This bird is of the light phase

and this one is of the dark morph

In this image we see all three phases together

All the images in today's blog were taken today over the Rock of Gibraltar

Not all were high and some, incredibly, flew low over the town

The passage continues and more species will pass over the next two months...

Thursday, August 4, 2011

Activity in the Strait of Gibraltar in mid summer

The Orca activity in the western end of the Strait at this time of the year is related to the exit of the Red Tuna from the Mediterranean towards the Atlantic. The tuna enter the Mediterranean in April to breed and leave in July and early August. The Strait is very deep, reaching 1000 metres, but in the west a sill rises from the sea bed and the depth is reduced to around 200 metres. Any fish passing this is forced upwards allowing a chance for fishermen (below) and orcas (above) to catch the fast fish.

One interesting aspect is that the highly intelligent orcas have learnt to go for the tuna which have been caught in the fishermen's hooks. It is not unusual for the fishermen to pull up a tuna head, rest of the body missing!

The groups of orcas seem to fuse and split at different times as they hunt for the fish. Here is a pod of females, recognizable by the small, curved, dorsal fins

Male (right) with higher fin than female (left)

Female with young

The Strait is a busy shipping lane so the orcas have to be alert to this danger at all times

Male Orca

Female starting a dive

Male showing the large fin clearly

While watching the orcas we picked up other activity which we illustrate from here down, with images from our own archives, taken in the Strait at other times. Here is a group of Common Dolphins Delphinus delphis

Loggerhead Turtle Caretta caretta

Common Tern Sterna hirundo - steady flow of birds migrating towards the Atlantic

Black Tern Chlidonias niger - The first birds are now moving into the Atlantic

Balearic Shearwaters Puffinus mauretanicus - coming from the western Mediterranean to feed in the rich waters of the Strait

Cory's Shearwaters Calonectris diomedea - also feeding in the upwellings of the Strait

Wednesday, August 3, 2011

Magical 24 Hours

The last 24 hours have been magical. Few places can offer what the Strait of Gibraltar can. Here an Orca Orcinus orca off Tangier, Morocco, this morning...Last night 10 thousand Black Kites Milvus migrans and up to 100 thousand Common Swifts Apus apus migrating south over the Rock of Gibraltar (below)

Part of a large flock of Black Kites yesterday

Black Kites against a backdrop of migrating Common Swifts

This is a quick news flash. These stories will be developed in future blogs...

Sunday, July 31, 2011

Raptor Migration in late July

We saw the last Black Kites Milvus migrans migrating north in mid-June. Now they're back, heading south for Africa with this year's youngsters!

For a few days now small groups of Black Kites have been crossing the Strait of Gibraltar as they head for the tropical African savannas

But yesterday evening, around 6pm we saw a big "rush" of birds over the Rock of Gibraltar. My friend Mario Mosquera estimated 1500 birds in the flock, a taste of things to come. With westerly winds these birds drift over Gibraltar from where they gain height to start the crossing. If the wind is too strong some turn back, often having already started over the sea, and try the next day.

Most of yesterday's birds were juveniles, birds that have been born this spring. You can tell them by the pale, rufous, plumage and the fresh wing and tail feathers. Breeding among the Iberian birds is timed to coincide with the spring abundance of food. The Iberian adult Black Kites arrive in February and early March. It is these birds, and their young, that are now leaving to avoid the summer drought. Their arrival in sub-Saharan Africa will coincide with the onset of the summer rains there.

Not everything is leaving after breeding. Eleonora's Falcons Falco eleonorae are just arriving in the area from their wintering grounds on the island of Madagascar. These rare and elegant falcons breed in remote islets and unfrequented coastal sites across the Mediterranean and the Atlantic coast of North Africa. They arrive late for a reason. Their young will hatch in September and will be fed on the millions of small migrating birds that will then be heading for Africa. It is a wonderful example of a perfectly tuned specialised strategy. It's not easy to find these birds on migration so it was a treat to see this female (above and below) yesterday at Europa Point.