Saturday, January 29, 2011

Diary - The Lammergeier

The Lammergeier has become among the rarest of European breeding birds. The decline seems to have started as far back as the 19th Century and its causes seem to have been a combination of the rise of guns, poisoning and nest robbing. Colonel Irby in 1895 wrote how his friend Colonel Verner had already noticed a decline twenty years earlier when "...these birds nested regularly not far from Gibraltar, but owing to persecution have of late years disappeared or retired to less-frequented sierras."

Dr Stark, in the decade of the 1880s recorded how "In Andalucia is decidedly common in the Sierra Nevada, and all the region between Granada and Jaen. In a day’s ride five or six may be seen flying over the hill-sides or gliding along the face of a cliff or down some ravine. In the Ronda mountains they are fairly numerous, becoming scarcer towards Gibraltar and Tarifa."

It seems that the presence of the Griffon Vulture was somehow detrimental to the natural distribution of the Lammergeier. Dr Stark thus commented how "In certain districts of the Sierra Nevada, where the Griffon does not intrude, the Quebrantahuesos is especially numerous."

Stark's comments also suggest that the population near the Strait of Gibraltar was dominated by non-breeding immatures (above and below). "In the lower ranges of the Sierra de Ronda, towards Gibraltar and Tarifa, the Bearded Vulture is not very common; the Griffon being, on the contrary, abundant in that district. The majority of Bearded Vultures seen here have been birds in dark plumage, not fully adult."

Today, to have any chance of seeing (and photographing) Lammergeiers we have to travel to the Pyrenees, the main European nucleus of this species. Re-introduction programmes, such as those in the Sierra de Cazorla, offer hope of recovery which will be slow. These birds take eight years to reach breeding condition.


First winter (left) and adult (right)

Today, in special places like Boumort in the Catalan Pyrenees, it is still possible to observe the complete array of European vultures together. Three of them - Griffon, Black and Lammergeier - are in this single photograph.

My gratitude to the management and staff of Boumort Reserve for permission to photograph within the reserve

Tuesday, January 18, 2011

Diary: The Bonelli's Eagle

With the new year I am introducing a new section to the blog called diary. Whenever this word appears in front of the post title it means I will be drawing on written texts from 19th and early 20th Century naturalists and comparing to the present. Photographs may not all be from now but will include some from my archive. Today, I start with the Bonelli's Eagle Aquila fasciata.

This impressive cliff-nesting eagle has attracted the attention of naturtalists for a long time. Sadly, this bird is very much in decline and is rarer each year. The European population is of the order of 1000 breeding pairs, 80% of which are in Spain with smaller numbers in Portugal, Greece, France, Italy, Croatia and Albania.

Its geographical range once included many coastal cliffs where it is now gone. A traditional site was the Rock of Gibraltar where it nested annually until last recorded in 1936 - the disturbance of the war years probably caused their disappearance. They nested below the old Signal Station (below).

Colonel Howard Irby in the second edition of his Ornithology of the Straits of Gibraltar (1895) tells us how " a pair nest annually at Gibraltar, at the 'back of the Rock', to the south of the Signal Station; there are never more than a pair, though there are four situations where there are nests, one of which has not been used for several years.

typical eyrie with two chicks

My friend and colleague Dr Juan Pleguezuelos of the University of Granada studied this habit of use of alternative nests and found that it was a way of avoiding parasite infestation. What is more he was able to show that birds which lined the nests with fresh branches of Maritime Pine Pinus pinaster had a greater breeding success rate. The chemicals produced by this pine acted as an effective insect repellent that kept the nests clean and the chicks healthy!

Bonelli's Eagles were once widely distributed across southern Iberia and our Pleistocene cave sites on the Rock have revealed evidence of their presence since at least 50 thousand years ago (above).

Irby tells us how "when not breeding they hunt together (male and female), one high above the other, suddenly stooping down on some luckless rabbit or else gliding off to take up a fresh aerial station whence to watch for their prey, which seems to be taken on the ground." The other favourite prey of this bird is the partridge.

Irby relates some fascinating accounts of situations and contexts unlikely to be found today. Ospreys also nested on Gibraltars cliffs and he tells us what happened when they came across each other: "on another occasion, in the same month, I saw a Bonelli's Eagle flying about not far from the Osprey's nest, when down swooped an Osprey, like a stone, striking the Eagle on the back and knocking out a lot of feathers. Shrieking out, they were bound together for a few seconds, and then separated, neither apparently the worse for the encounter, and each flying off towards their respective eyries.

Lt Colonel Willougby Verner, writing in 1909, was equally impressed by this powerful eagle. As a falconer and son of a falconer he "was intensely attracted by Bonelli's Eagle when I learnt that it was the same species which the Afghans employ for hawking small deer."

He further observed "as regards their structure, few Eagles, if indeed any, are so powerful for their size as is Bonelli's. Their massive legs and feet and abnormally large claws are seemingly out of all proportion to the rest of their body." 

It is a real pity that such a majestic animal should be suffering such a fate as we progressively eat into their territories and sever traditional connections that have maintained viable populations for tens of millennia...

Monday, January 3, 2011

The Chiffchaff and the Aloe

South African aloes were introduced in Gibraltar in the 19th Century. They did well in the Mediterranean climate, similar to that in their home, and spread. They fared best on warm limestone slopes.
The mild, frost-free, winter climate of Gibraltar has allowed the aloes to flower in December and January, the corresponding South African summer.
the slopes take on a spectacular colour as the stands of aloe come into full bloom

These aloes are pollinated in their native South Africa by sunbirds, which have coevolved with the plants and have developed specialised bills for extracting the nectar. The red of the aloes attracts the birds and pollen is transferred by the birds who get their nectar reward. There are no sunbirds in Gibraltar but some species have learnt, in the short time since the 19th Century, that the red aloes mean food.

The main species visiting the aloes is the Chiffchaff, a winter visitor. It seems that the nectar is used as supplement to their usual diet of insects.
Chiffchaffs (above and below) drinking nectar

The Sardinian Warbler, a local resident, is another regular visitor to the aloe stands (above and below)

Sardinian Warblers (male above and female below) are larger than Chiffchaffs and will supplant them from the flowers

but the Chiffchaffs have a trick - they hover and collect nectar from the flower heads that are inaccessible to the heavier Sardinians
So the sunny slopes of Gibraltar in late December and January are a little laboratory with a natural experiment in action. Here we observe a behavioural change in the behaviour of bird populations, both migratory and resident. And, while for a long time the aloes seemed unable to cross pollinate and only spread vegetatively, there is clear evidence now that plants are getting fertilised. The Chiffchaffs are doing the trick, it seems!

Butterfly on aloe - with the warm weather (temperatures around 20C in the middle of the day) many insects are active around the flowers too, providing additional temptation to the insectivorous warblers