Wednesday, August 18, 2010

Swifts in an Attic

2000 pairs of Pallid Swifts breed each year in Gibraltar. They are the great masters of the air, only coming down to breed. These birds spend their lives in the air where they catch airborne insects - they live off aerial plankton.
They arrive at the end of February and leave in October, some staying into November. So they're not away for long and they don't go too far either. Most winter in the Sahel region, south of the Sahara. Breeding usually starts as soon as it gets warm and varies from year to year. First clutches average three eggs and second clutches two eggs. Once the first brood fledges many pairs return to the nest for the second brood of the year. This is unusual among swifts. Common Swifts, even in these latitudes, raise only a single brood.
All swifts have a problem when the time to moult arrives. Spending most of their time on the wing, they need to moult the flight feathers slowly. It takes a long time. Pallid Swifts starting a second clutch, in late July and August, cannot wait until they raise their young to moult. Once the young are fledged they have to migrate. They live on the limit. So they have to start wing moult while breeding. Notice the adult on the right (above) has started moulting the inner primaries (which look darker).

But before they can start a second time they have to encourage the first generation out of the nest holes. A juvenile Pallid Swift (above) peeps out wondering what the fuss (below) is all about!


Juveniles (above and below) are easily recognised by their scaly plumage, primaries and wing coverts having pale edges. Notice the large eyes, ideal for spotting insects in mid-air.

The task of feeding chicks requires special consideration when you spend your life in the air. Swifts collect insects in their wide mouths and bring back large food balls, glued by saliva, which may contain several hundred insects at a time. This technique reduces on travel time to and from the nest and also allows the adults to range widely away from the nest in search of food.
 They are the masters of the air, experts at catching small insects and hunting in packs, like wolves or orcas.
And their streamlined bodies, millions of years of evolution, are perfect for the job






2 comments:

  1. Thank you Clive for a truly excellent blog. As allways they are interesting, informative and accompanied by superb photographs. Keep up the good work.
    Mal

    ReplyDelete
  2. thanks Mal! I'll keep trying!

    ReplyDelete