November 10, 2015
Swallows and House Martins rest in the Valle del Genal before crossing the Strait of Gibraltar and Morocco (Nth. Africa) and beyond.
Homeward-Bound Travellers Challenge The Powers of Nature
If you were a bird, how would you plan your annual, long trip south? Would you chose a familiar route or do you prefer a change of scenery? Would you travel in a group or strike out alone? Would your route include ventas and supermarkets you have already sampled or do you like the thrill of the unlocated, untried and untested? If your trip includes little ones would you plan to make the journey as safe and sure as possible or more thrilling? What have you noticed about the nature of birds you have seen around since spring? Are they habitual and cautious or are they thrill-seekers?
Unlike their British counterparts, Spanish Red Kites migrate – Costa de la Luz.
The migrating birds of all sizes choose familiar routes. They are able to recognise landmarks and use them as we do as points of reference and the young birds learn the route when they travel with their parent birds and as part of a flock which provides safety in numbers. The other benefits of taking a familiar route include knowing where to find food and where to be on alert for danger. The easiest route for the birds to take is that which includes the shortest distance across the Mediterranean which is at the Strait of Gibraltar and this means the spectacle of watching thousands of travelling birds can easily be enjoyed at locations in Gibraltar and the environs of Tarifa.
A Short-toed Eagle negotiates the blades of the Tarifa wind farm.
The smaller, passerine birds that are leaving with this year’s young birds have regrouped into flocks that merge with other flocks of similarly-sized birds headed for The Strait of Gibraltar. In the vicinity they continue feeding and sizing up the local weather. An ideal forecast for their trip over the water would include calm, dry conditions with a tail-wind to blow them across but a glance at the wind-turbines that punctuate the hills and mountains along the Strait shows that the winds that blow are strong and constant enough to be harnessed to create electricity and are generally easterly and westerly. Besides the challenge presented by the weather, large flocks of small birds attract non-migratory birds of prey who capitalize on the influx of feathered food and thin out the numbers performing the crossing.
White storks raise of thermals in formations known as “kettles”
The passerine birds, excepting Bee-Eaters, traverse The Strait under cover of protective darkness and at higher altitude, where they find favourable air-streams, but birds of prey (raptors) and larger birds such as storks cross by day. Whilst these birds may appear physically more up to the sea-leg they too have to test out the prevailing weather and especially could not risk a strong Levanter (easterly) wind blowing them out into the Atlantic. For birds that glide on the uplifting thermals (created as warmed air rises off the ground) the need for optimum wind conditions is imperative. Thermals are very weak over water and the birds must flap to keep air-borne; this intensive effort can use nearly nine times more energy and therefore needs to be kept to a minimum. Whilst watching the Tarifa migration last year, a Kettle (a flying group ) of storks was observed moving out over the sea to a distance of a couple of kilometres and then circling back as the group decided to wait for better conditions.
A long list of raptors that includes: Sparrowhawk, Honey Buzzard, Egyptian Vulture, Short-Toed and Booted Eagle are thrilling to spot as they leave Spain until next spring. If they haven’t been caught by the wind-turbines they cross in groups leveraging the height of the mountains to launch themselves further over the water minimising the effort they have to expend or wait for the thermals to build up towards afternoon to lift them to altitude and find an favourable air-stream to power them to Morocco from whence they will continue south across mountains and the great desert of the Sahara.
If you would like the opportunity to follow migrating birds (albeit taking different routes) this link will provide you with satellite tracking of ospreys headed to central eastern Africa from the UK:
Birdwatchers and twitchers from all over Europe gather along the Strait of Gibraltar to observe the migration.
Words: Fee Brookes – Images: © Geoff Simpson
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