Wednesday, 23 July 2014

Convergent evolution

It is a common thread of evolutionary theory that unrelated animals subject to the same requirements will evolve into similar forms. Swifts and Nightjars (although they aren't strictly speaking unrelated) show this very well as both are aerial insectivores and share features suited to this way of life, streamlined head, big inset eyes, small beak, long wings and short legs 

and of course big mouths!

Yesterday demonstrated very well though that although they share similar body forms certain aspects of their lives still differ greatly! At midday on one of the hottest days of the year so far, I found myself crawling through the cramped, dust-filled, attic of a large Victorian house in Rhayader in search of swiftlets. 

Chim chiminey, chim chiminey, chim chim cheroo - the aftermath of a successful swiftlet ringing attempt and a brief taste of what a Victorian chimney sweep's life must have been like. Some of you may not be able to see the difference!!

Swift nests are very easy to locate, by the screaming parties of adults circling the building, but are usually nigh-on impossible to access in the deep recesses of a cavity wall or in a narrow gap atop the wall-plate. So it was very pleasing to discover that at least two of the half-dozen or so nests in this building were (relatively!) easy to get to and four young Swifts were ringed along with one brooding adult.

An adult Swift with its three chicks. Swifts incubate from the first egg and so the chicks are usually stepped in size with the younger ones not making it in a bad year.

Both Swift and Nightjar chicks can lower their body temperatures and go into a state of torpor to enable them to survive short periods of bad weather when the adults may not be able to catch sufficient insects to feed a growing brood.

Although Swifts never land they still manage to collect nest material floating about in the air and construct a very reasonable nest of this all held together with a bit of Swift spit.

A Swift nest is made entirely from building materials blowing in the wind!

I will be going back after the Swifts have left for their African winter quarters to investigate the possibility of installing nest boxes to increase the number of pairs using the building.

Nightjar nests on the other hand are extremely easy to access as there isn't actually any nest. The eggs and young are just placed directly onto the ground. They are however incredibly well camouflaged and the adults have perfected their behaviour so as to avoid giving away the nest site to any potential predator and unfortunately that includes BTO nest-recorders and ringers!!

Spot the Nightjar nest!

These two Nightjar chicks are also clearly visible in the photo above

A few days older and ready to ring

and weigh!

This year, with the able assistance of Paddy Jenks, we are working on three separate Nightjar sites, one in North Wales, one in South Wales and one in West Wales.  Last night I ringed our 47th Nightjar of the year and found the 19th nest so despite their best attempts  things aren't going too bad !!

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