Pallid Swifts

Pallid Swifts in nest in Gibraltar Museum attic last night. Male joined female for the first time and they interact with mutual preening:

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Another fall of migrants

The post of 7th March recorded an early fall of migrants and the conditions that created such gatherings. We had another one today, again with light easterlies, mists and light rain. The dominant species were Chiffchaff and Willow Warbler, many feeding side-by-side, but there were plenty of other species. I managed to photograph most of the ones where I was except for a skulking Nightingale that eluded me! Here are the main species in today's fall:

Chiffchaff: still very plentiful. These birds are probably coming in from sub-Saharan Africa, where a good number spend the winter, and are probably bound for north-western Europe - Holland, Germany, Switzerland, United Kingdom

Willow Warbler (above and below): These are all returning from tropical West Africa and are heading for western Europe, Scandinavia and the Baltic

Common Whitethroat (above and below): one of the commoner species today. Incoming from tropical West Africa and heading for western Europe including the British Isles

Common Redstart (male above and heading this post and female below): Incoming from tropical West Africa and heading for north-western Europe as far as Finland

Subalpine Warbler (above and below): still coming through in good numbers and has been the subject of earlier posts

Woodchat Shrike (above and below): building up numbers (see yesterday's post)

The breeding Sardinian Warblers (above and below) and Blackcaps (far below) carried on with their domestic duties not too bothered by the sudden influx of strange neighbours!

The last of the Robins are also moving through, bound for north-western Europe, east to Poland and Switzerland

Shrikes on the move

March is migration time for Woodchat Shrikes across the Strait of Gibraltar and they will reach their peak during the middle of April. These gorgeous birds are western European, largely Iberian, breeding birds but are from as far as Germany and Switzerland. They often pause to refuel and like the edges between woodland and open ground, like on these olives this evening on Gibraltar. From these perches they will pounce on insects, lizards or even small warblers.

The Woodchat is the most abundant of Iberian breeding shrikes. The larger Southern Grey Shrike (archive photos below) is largely sedentary and replaces the Woodchat in habitats with fewer trees. It is genetically distinct from the Northern Grey Shrike, which reaches the area in the winter, and are curiously most closely related to the North American Grey Shrike.

This species complex requires further revision. The Canary Island, North African and Central Asian forms seemingly good species.

Two other shrikes breed in northern Spain and perform migrations in south-easterly direction in the autumn which takes them to wintering grounds in East Africa. They are the Lesser Grey Shrike and the Red-backed Shrike (archive photos below). The Red-backed Shrike is a common breeding bird in Cantabria but these birds migrate east across Europe and south into East Africa which means that Red-backed Shrike sightings in the south of Iberia are few and far between.

Migrants and Residents

Subalpine Warblers have been coming through the Strait for almost a month now, first the males (see post of 7th March) and then females. The males move in first to secure the best breeding territories, those that will attract the best females. The closely-related Sardinian Warblers (below) are, instead, largely resident so the males have by now set up territories and are in nesting duties with the females.

The picture is not that simple though. Some Sardinian Warblers, from the northernmost populations, actually migrate south and even cross the Sahara Desert to winter in tropical West Africa. But they are a minority whereas the Subalpine Warblers all migrate to sub-Saharan Africa.

The Subalpine Warblers (above) arriving in Gibraltar now have completed the long crossing of the Sahara Desert and are lean. They feed frantically to recoup lost weight before embarking on the final lap of the journey into Iberia or southern France. They may come up against the local, larger, Sardinian Warblers (below) but there is rarely any territorial interaction between them. The migrants tend to skulk and keep a distance from the residents.

By and large Sardinian Warblers live in the milder lowlands and are able to survive the winters. The smaller Subalpine Warblers arrive once the Sardinians have set up territory so they move into a different habitat or region. Sardinians are at home in Mediterranean scrub whereas Subalpine Warblers occupy scrub with scattered trees. The Subalpine Warblers also occupy higher altitude and continental interiors which are inhospitable in the winter. Under present climatic conditions the two species are finely balanced and neither gains at the expense of the other.

Sardinian Warbler male (above) with black hood; female with grey hood below

On the top of the Rock

Gibraltar offers many opportunities to observe the interaction between nature and history. The very top of the Rock, 426 metres directly above sea level, is a very special place in this regard. I took the opportunity of a visit that we had organised to a very special place to take some photographs.

Gibraltar has over 30 miles (over 60 kilometres) of tunnel, some excavated in the 18th Century but most of it during the Second World War. A veritable city was dug into the Rock. But it was only a few years ago that some very special and secret tunnels were found. They are so sensitive to disturbance that we have kept them closed to the public and we only organise two or three visits per year. Yesterday was one such day.

The point about these secret tunnels is that they were excavated within another set of tunnels. Very few people were aware of their existence and it all seemed a myth until they were rediscovered over 50 years after the end of the Second World War.

The plan was that, should the Nazis overrun Gibraltar, six men would brick themselves inside these tunnels from where they would spy on movements outside and report back to London. Silence and stealth were essential as the potential enemy would be marching past along tunnels literally inches away!

The floors, unlike any other tunnel, had floors lined with cork tiles (above) so that any noise from walking was buffered. Every eventuality was catered for. Rain water collected from the limestone was stored in a hidden tank. When I first went in, after it had been closed for over 50 years, the tank still held water and the tap, like yesterday (below), still worked!

We found the remains of a bicycle, with a leather chain to minimise sound, that would provide for exercise while generating electricity and help ventilate the tunnels.

The air was circulated through a shaft (below right)  from the exterior and a copper cable within a sheath (below left) was put out onto the cliff at night to transmit information.

This section of the tunnel led east onto the cliff face. From the slit ships in the Mediterranean could be observed. The stairs doubled on themselves with a second tunnel leading west (below) from where the Bay of Gibraltar could be observed.

The location was crucial. Being at the very top of the Rock, observation points that looked west and east could be situated within the same complex. In the end the tunnels were not needed but remained sealed, and eventually forgotten, during the cold war.

On the outside are the huge 9.2 inch guns that could hit targets on the North African coast, 21 kilometres away, of the Strait of Gibraltar. The channel could be effectively closed from here.

Today, the cliffs are part of a huge Yellow-legged Gull colony but before the Second World War Bonelli's Eagles and Egyptian Vultures nested here. Disturbance drove them away.

Beatiful rock-dwelling wild flowers are now out and include the endemic Gibraltar Candytuft Iberis gibraltarica (above) and the Giant Squill Scilla peruviana (below)

Giant Squill (above ) and White Mignonette Reseda alba (below)

The swifts are back on their nests

For many years, now over thirty years ago, I studied the colony of Pallid Swifts in the attic of the Gibraltar Museum. Last year we put two infra-red cameras on two of the nests. Here are some photographs from one of the nests from the night before last. Although the Pallid Swifts have been about since the beginning of February, it is only now that they have started to come close to the colonies in the evenings and visiting the nests.

The adults return to the same nest, which they repair, year after year. They do so for over twenty years in some cases. Many Pallid Swifts raise two broods in good years, the last young flying in October. In contrast, Common Swifts in Gibraltar only raise a single brood.

Only the female visits the nest at first and sleeps on it. The males sleep on the wing. In time the males accompany the females at the nest and they take it in turns to incubate and feed the young. We shall follow these nests all spring and see how successful they are this year.