Winging off for warmer climes
Lone raptor soaring above the city of Barcelona -- Picture: Assumpta Bosch (Click twice on picture for a full-screen blow-up)
Bird’s-eye Barcelona basking in the glare of an early Autumn morning sun was a stirring sight, viewed 430 metres (1,410 feet) up the Turó de Magarola, one of the peaks of the Collserola mountain range running smack within the heart of a city of 3 million. But it was not what we had come to see. The sight that held the collective attention of birders and ornithologists on the hilltop watchsite was that speck in the southern sky, on the upper right corner of the picture above. It was a European Honey Buzzard (Pernis apivorus) spiralling leisurely upwards. Minutes later it had disappeared overland on the first leg of its long flight to central Africa for the winter.
The Honey Buzzard was one of more than 1,300 birds of prey that have abandoned their summer roosts in Catalonia and migrated south for the warmth of the Sub-Saharan plains. Over the last two weeks of September the skies over Barcelona have been full of them, providing an annual spectacle that has caught the imagination of bird-lovers and the simply curious alike.
Portside Barcelona with the Collserola mountain range straddling the length of the city - Photo courtesy of Wikipedia
(Click on picture for an enlargement)
(Click on picture for an enlargement)
The Turó de Magarola is one of the five peaks of the Collserola, an 84 sq kilometre mountain range that that has been designated a national park and which forms part of the coastal ranges separating the city from the valleys to the north and the plains to south. The Collserola’s tallest peak and highest point of the city is the 512m Tibidabo peak, location of the century-old amusement park with the same name. The Collserola mountain lies just below one of the major flyways for broad-winged migrants. Flyways are long-distance avian flight paths which span continents and oceans and where the phenomenon of hundreds and even thousands of birds flying in formation is observed. GOT members were out of luck however; no significant flypast materialised during the long September 25 morning we were on Magarola peak. All we saw – before the searing midday sun sent us scuttling downhill -- were isolated individuals and pairs circling around, waiting for the right weather conditions to start them off on their long hauls. Birders from local clubs affiliated to the Catalan Ornithological Institute (Institut Català d'Ornitologia, ICO) have been painstakingly recording the species and their numbers using the Barcelona flyway since the migration began at the onset of autumn on September 3. And their findings have brought some surprises. Honey Buzzards, for one thing, turned out to be the largest group migrating from Catalonia, followed by Marsh Harriers (Circus aeruginosus) and Common Kestrels (Falco tinnunculus). In all, a total of 19 species of birds of prey flew past the Magarola peak over a period of four weeks. Among them --- spotted for the first time in 17 years -- was the Short-eared Owl (Asio flammeus), one of the very few nocturnal birds of prey that migrate south for the winter.
European Honey Buzzard (Pernis apivorus) –Picture by ornithologist Roger Sanmarti, courtesy of Photologistics
ICO chart showing the flight route of the European Honey Buzzard
Common Kestrel (Falco tinnunculus)-- Picture by ornithologist Roger Sanmarti, courtesy of Photologistics
The principal broadwings using the Collserola flyway between September 3 and October 2 this autumn were the:
Black Kite, Milvus migrans, Milano Negro, Milà Negre, Schwarzmilan, Milan Noir.
Booted Eagle, Hieraaetus pennatus, Aguililla Calzada, Àguila calçada, Zwergadler, Aigle botté
Common Buzzard, Buteo buteo, Busardo Ratonero, Aligot comú, Mäusebussard, Buse variable
Common Kestrel, Falco tinnunculus, Cernícalo Vulgar, Xoriguer comú, Turmfalke, Faucon crécerelle
Eurasian Sparrowhawk, Accipiter nisus, Gavilán Común, Esparver vulgar, Sperber, Épervier d'Europe
European Honey Buzzard, Pernis apivorus, Abejero Europeo, Aligot vesper, Wespenbussard, Bondrée apivore
Eurasian Hobby, Falco subbuteo, Alcotán Europeo, Falcó mostatxut, Baumfalke, Faucon hobereau
Marsh Harrier, Circus aeruginosus, Aguilucho Lagunero Occidental, Arpella vulgar, Rohrweihe, Busard des roseaux
Merlin, Falco columbarius, Esmerejón, Esmerla, Merlin, Faucon émerillon,
Montagu's Harrier, Circus pygargus, Aguilucho Cenizo, Esparver cendrós, Wiesenweihe, Busard cendré
Northern Goshawk, Accipiter gentilis, Azor Común, Astor, Habicht, Autour des palombes
Northern (Hen) Harrier, Circus cyaneus, Aguilucho Pálido, Arpella pàl·lida, Kornweihe, Busard Saint-Martin
Osprey, Pandion haliaetus, Águila Pescadora, Àguila pescadora, Fischadler, Balbuzard pêcheur
Peregrine Falcon, Falco peregrinus, Halcón Peregrino, Falcó pelegrí, Wanderfalke, Faucon pèlerin
Red Kite, Milvus milvus, Milano Real, Milà reial, Rotmilan, Milan Royal.
Short-toed Eagle, Circaetus gallicus, Culebrera Europea, Àguila marcenca, Schlangenadler, Circaète Jean-le-Blanc
Eleonora's Falcon, Falco eleonorae, Halcón de Eleonora, Falcó de la reina, Eleonorenfalke, Faucon d'Éléonore
Griffon Vulture, Gyps fulvus, Buitre Leonado, Voltor comú, Gänsegeier, vautour fauve
Black Stork, Ciconia nigra, Cigüeña Negra, Cigonya Negra, Schwarzstorch, Cigogne noire
White Stork, Ciconia ciconia, Cigüeña Blanca, Cigonya blanca, Weißstorch, Cigogne blanche
Broadwings weren’t the only ones migrating via the Collserola fly-path. Ferran counted 10 Barn Swallows (Hirundo rustica), 10 House Martins (Delichon urbcum), 2 Alpine Swifts (Apus melba), and even 2 Grey Wagtails (Motacilla cinerea), something not so normal, as these passerines use flyways free of raptors to head south.
Chart designed by ICO ornithologist Anna Dalmau for GOT’s 2011 World Bird Day celebrations October 2.
For example, Barn Swallows (picture A) use the flight routes shown in chart A.
For example, Barn Swallows (picture A) use the flight routes shown in chart A.
(Click on picture for an enlargement. Clicking again on the enlargement gives a full-screen blow-up)
Easy picking for this falcon
The reason why birds migrate can be guessed at. Warmer weather is a strong inducement, but the primary motivation for migration appears to be food. While the long northern summer is ideal for breeding birds to feed their young, as days shorten in autumn, it is in the south where available food supplies varies little with the season. How migrant birds know when or where to travel is, however, one of the greatest mysteries of nature. Yet their epic flights over continents and oceans are as predictable as the seasons, and have been extensively charted. From Catalonia, for example, the flights of little songbirds like the robin have been just as gruelling as any undertaken by broadwinged birds of prey. While the risks are enormous for both big and small, the latter face an extra hazard – predation. Passerine birds flying south, for instance, are easy picking for the Eleonora’s Falcon, which breeds on Mediterranean islands, and feed their young with captured migrants. Death takes a heavy toll on all travellers however, and it is estimated that half of all migrants heading south for the winter will not return to breed in the spring. Apart from predation and bad weather, high stress and `physical exertion, man-made dangers also raise the migrant mortality rate. Birds crash full tilt into the glass panes of skyscrapers by the thousands, mistaking the reflection of the sky in a window for the real sky, get caught in wind farms, killed by power lines, and trapped or shot down by hunters. But all these dangers pale before that of potentially the greatest threat of all – the loss of stopover habitat. Most birds have to break journey to rest, stock up on food, and shelter from predators and inclement weather. Rapid urbanisation, deforestation and modern agricultural practices however have meant the disappearance of many stopover sites. And without them, many migrants will not make it.
Unpowered flight
Most migrations begin with the birds starting off in a broad front, that is, starting from different parts of the region. This front generally narrows into one or more flyways. While small birds can depend on pure wing-power to propel their light bodies, the heavier land-bound broadwings need favourable weather conditions such as rising air currents to stay aloft. On long hauls, birds of prey such as eagles, falcons, vultures, buzzards and kites wait for warm columns of air called thermals to help them out.
This WIKIMEDIA COMMONS graphic illustrates what a thermal column between the ground and the cumulus cloud (A) looks like. The sun increases the temperature of the ground which will then warm the air above it (1). The bubble of hot air starts to rise (2) until a certain point where it will cool down. Due to its lower temperature, the mass expands and moves downward (3). Thermal columns are completely invisible phenomena. They are onland phenomena and cannot form over water. Chart courtesy of:
Master gliders
Raptors detect these thermals and simply hop on them. As the thermals form beneath their outstretched wings, they circle slowly and effortlessly higher and higher with the rising warm air until they reach the top of the column, generally around one and a half kilometres (about one mile) above ground.
Thermal hopping and long-haul gliding on flatland -- illustration on a Magarola peak information board
When the thermal fizzles out, the birds break out of the column, draw in their wings, fold their tails and begin their long glide – an energy-conserving unpowered flight with wings fixed in place and no flapping. As they glide and lose altitude they look for another rising thermal to ride and regain altitude for the next glide. It is a continuous process and a vital means of long-haul transportation for broadwings.
Indeed, few bird species can better the broadwings at gliding. Once atop a thermal they can glide almost 18 km (11 miles) before they sink to the ground. Tailwinds -- winds that blow in the direction of travel – provide added impetus. With a strong tailwind to boot, broadwings can cover hundreds of kilometers in a few hours. -- Report by ABUL FAZIL
Absolutely fantastic wanderings into the wonderful world of nature in all it's beauty and splendour.Thanks for taking us there while in our corner.
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