Monday, May 31, 2010

Portrait of a Wetland III

Continuing with our selection of species from the marismas, today it's the turn of one of the most elegant of its inhabitants - the Purple Heron. A ground nester, usually deep in the reeds, this year has provided ample cover for these birds to nest in.

This bird arrived from south of the Sahara in March. Like many of the other wetland migrants, for example the Collared Pratincole, this bird attempts to raise its young before the start of the dry season. That is now with us and temperatures are soaring into the upper 30s in the shade. In the treeless marismas it is a stressful time. By July these wonderful birds, along with the pratincoles and others, will be on their way south and we will have to wait another year to see them once again.

With so much water around we might expect the birds to be scattered but it seems that some ponds and pools are better than others and these are the places to see the gatherings. Purple Herons are often found alongside Little Egrets.

Friday, May 28, 2010

Portrait of a Wetland II

Continuing with our exploration of special species that breed in the marismas (marshes), today I post photographs of the Collared Pratincole. This species is a trans-Saharan migrant which winters in the Sahel and semi-arid areas south of the Sahara Desert's edge. The birds that breed in the marismas arrive during the course of March. These photographs have been taken between March and May this year.

Collared Pratincoles nest in colonies, usually between 20 and 30 pairs but sometimes more. They are scattered across the vast steppes, dry salt marshes and other arid open areas on the edge of the marismas. They are never far from water. They nest on the ground and feed by catching insects in the air.

Collared Pratincoles are highly social and noisy. Watching a breeding colony is an exhilarating experience as birds to and fro noisily. The arrival of the male back to the nest is marked by a posturing display (below) which reveals the spectacular chestnut underwing.

When seen on their own, male and female may seem indistinguishable from each other. But when together at the nest (below) the larger male (back) is clearly distinguishable from the smaller female.

The Collared Pratincole remains an abundant and colourful bird of the marismas. Let us hope that they continue to grace its skies for a long time.

Portrait of a wetland I

I return to the marshes of the lower Guadalquivir and I will dedicate the next few posts to some of the special species that live there. The marshes are now splendid. After the record winter rains, the early spring saw an excess of water in many parts of these wetlands. It is only now, that water levels are receding and aquatic vegetation taking, over that birds are breeding. Geraldine and I spent many hours there last Sunday. We have never, in all our years of fieldwork, seen the marshes as splendid as this year so they deserve some time dedicated to them.

The first batch of 2010 generation Swallows is now out (above) and the abundance of flying insects will ensure survival of many young birds. Soon the adults will be starting a second clutch. Curiously, today I saw Swallows coming in from Africa heading north, probably to the northernmost European populations. So, some Swallows have not arrived in the breeding grounds yet while others have raised a brood!

So the next few posts will focus on the wetland's gems. Today, it is the turn of one of the scarcer herons. The following pictures (and that at the head) reveal the beauty and elegance of the Squacco Heron.

Tuesday, May 25, 2010

Iberia - at the crossroads between Europe and Africa

In recent posts, with the brief interruption from migrating Griffons, I have been looking at the Iberian mountains. Today I want to expand this theme a little and gradually get us back to the lowlands. The photographs have all been taken within the last month, barring some of the Blue Rock Thrush which were earlier. The northern Iberian mountains - the Pyrenees and Cantabrians - are the most southerly outpost for some birds that are typical of the forests further north. They belong to what biogeographers call the Eurosiberian zone, distinguishable from the Mediterranean zone to the south. The Eurosiberian, definable by climate characteristics, penetrates Iberia in these mountains and is marked by trees typical of western Europe and not the Mediterranean. Among the species that breed here, in their most southerly outposts, is the beautiful Bullfinch. The photographs (above and below) were taken in the Pyrenees so these are southerly Bullfinches!

But some species, typically those of more open habitats, have managed to penetrate (or at least survive the global warming that followed the last ice age) further south. We already met the Bluethroat (above) in our post of 30 April and another species typical of these mountain shrublands is the Hedge Accentor (below). Broadly speaking these are Eurosiberian birds that find adequate habitat in mountain peaks.
There are, of course, some remarkable Eurosiberian species that are able to live even in the lowland humid forests deep in the south-west, but they are not many. The European Robin is an example (below).

But not all Iberian mountain birds follow this pattern. The Red-tailed Rock Thrush (above and below) is a species that is typical of the chain of mountains that runs from Iberia eastewards to the Himalayas. I call this the mid-latitude belt (MLB) and it has its own set of species. These are not Eurosiberian birds, they are birds of the MLB, which in the west we equate with the Mediterranean mountains.

The closely-related Blue Rock Thrush is also a species of the MLB and it gives us a great comparison, a natural experiment, with its cousin. The Blue Rock Thrush is resident across many rocky areas, hillsides and low mountains in the western part of its range. Blue Rock Thrushes from the north and the more continental eastern parts are migratory. But in the mild west they can survive the winters without migrating. The smaller Red-tailed Rock Thrush is fully migratory, crossing the Sahara Desert to winter in tropical Africa. It seems to obey an unwritten rule which is that in closely-related species the smaller one migrates more than the larger. It could be a signal of competition between the species in some distant past or it might be that the larger species survives the northern winters better - having a lower surface-to-volume ratio which reduces heat loss. The net effect is that a lot of suitable but empty rock thrush territory opens up in the spring. Some may be filled by Blue Rock Thrushes moving up the slopes but most is left vacant. When the Red-tailed Rock Thrushes come in from Africa in April there is not much for them low down where the larger Blue Rock Thrush is by then established in breeding territories. So these birds find most opportunities high up in the mountains, in places that were inhospitable in the winter and could not support any kind of rock thrush.

Thrushes and chats are very versatile and Iberia, with its wide range of climates and habitats, harbours many species. Away from the mountains, at the other end of the climatic gradient, is an MLB species that is at home in the warmest and drier climates within the Mediterranean zone. It is, not surprisingly, among the last to arrive in spring from sub-Saharan Africa. The Rufous Bush Chat (above and below) is thus at the opposite end of the Iberian climatic gradient from its cousin the Bluethroat. They are here with us now and provide us with a good bridge to future posts that will return to the lowlands. Because we have accummulated a lot of material in recent weeks, when fieldwork has been intense, I will speed up the next few posts. So keep visiting!

Saturday, May 15, 2010

Wow, what a day!

Today I'm breaking from the usual format of this blog and from the mountain theme of recent posts. I just want to share with you one of those great days of migration, full of heart-stopping moments, that come from time to time. The winds over Gibraltar on Friday 14th May were strong and from the north-west. The temperature was cold for the time of year, starting at 13C at 7am and only rising to 20C. The strong winds kept the feeling of cold.

The morning started with one of those "rushes" of Honey Buzzards (above and below) that are typical of their peak migration. Seeing the birds coming towards me from all directions, level with me, giving me head-on views was the first heart-stopping moment. These rushes are probably early starts for birds that have gathered in roosts and then the day continues with a trickle of birds interspersed with flocks, building again to another evening "rush". The wind kept the birds really low over the sea. Even the sturdy Honey Buzzards were having trouble crossing the 14 kilometres of sea from Africa, and were being drifted 21 kilometres towards me on the Rock of Gibraltar. Hundreds and hundreds came in this morning surge.

Honey Buzzards are the last of the spring migrants and these are bound for Scandinavia and other parts of western Europe.

But these are not the only migrating raptors now and this is the time for a peak migration of immature birds of large raptors. The adults have moved north two months ago and now the young birds, that will not breed, are coming back. They only fly when it's hot, giving them thermals for height as a sea-crossing is even more precarious than for the smaller Honey Buzzards. So I returned to my watch point at Europa Point, Gibraltar's southernmost tip, at lunchtime only to be disappointed by the few birds coming through. It seemed the wind was too strong and the temperature too low. I had given up for the day but decided to have another go in the evening, around 6 o'clock. At first all seemed quiet but soon the outlines of large Griffon Vultures loomed over the sea heading in my direction! This was the second heart-stopping moment of the day!

In came the massive birds, each time closer, 60 or so. And almost without warning the apparently slow flyers were over us and the camera shutter was working overtime!

Many went straight through but some were clearly weak and struggling, looking for places to come down. And, of course, the local breeding gulls would have none of it!

The smaller but aggressive gulls give no quarter. I cannot explain the feeling of a 9-foot wingspan Griffon just over me with a gull landing on its back and pecking it. Here's the picture - note one of the gulls wings is actually below the vulture's!

and so they came tumbling down!

each time more of them!

and they were all around me, landing, flying low above, level and below me!

a bird up on the scree caught my I and I started to climb. Then, another heart-stopping moment, unbeknown to me an immature Short-toed Eagle had been sitting on the cliff and now took off to fly over my head, a few feet away!

hurry, enemy coming after you!

the Griffon mayhem continued through this brief pause

close encounters!

I left three griffons on the cliffs. They'll probably roost there overnight.In all, around 100 came in within an hour. Late Honey Buzzards and Black Kites kept coming through...

...and as the sun was going down and it seemed all over, another moment! Suddenly out of nowhere came a flock of migrating Common Swifts and soon they were all around us!
what a day!