Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Tuesday, September 20, 2011

Footprints of Evolution

This is the foot of a White-throated Treecreeper. (Cormobates leucophaeus)
It is listed as being in the "family" Climacteridae (which name obviously refers to its climbing ability).

This bird is in the Order: Passeriformes. That puts them amongst a huge group of birds known as "perching birds", but the name itself derives from the European bird, the House Sparrow (Passer domesticus) which is familiar in many Australian cities and country towns.

The most obvious feature of this foot is the huge rear toe nail. The other toe nails are also strong, and over-all the foot is large, relative to the body of the bird.
Foot of the White-throated Treecreeper
These bird are noted for their habit of flying to the base of a tree, and climbing up the trunk, in a spiral manner, searching under loose bark, and in crevices, looking for spiders and insects. That's what they do. Having huge powerful feet, and especially elongated and powerful toenails is clearly an evolutionary advantage for them.

By contrast, this is the foot of a Painted Button-quail.(Turnix varius)
Foot of a Painted Button-quail - lacks a hind toe.
These birds (Button-quails) are more-or less universal in distribution. They inhabit warm grasslands in Asia, Africa, Europe, and Australia (not the Americas). They are a group of small terrestrial birds. The genus Turnix superficially resemble the true quails of the genus Coturnix, but differ from them, in lacking a hind toe.

The relationships of the Button-quails (Turnicidae) have long been unclear, having been placed variously in their own order, or with the Galliformes (birds related to "Chooks") or Gruiformes (birds related to Cranes). Recent studies have shown that the button-quails are actually related to the Gulls and Terns and their relatives (Charadriiformes). There are 16 species of button-quail, ranging through Africa, southern and south-eastern Asia and Australasia.
Whatever their real ancestral heritage (waders or gulls and terns), they have adapted to a life in dry country. They are apparently not at all related to the similar-looking quails and pheasants and the very familiar birds we know as "chooks". One only needs to recall the "so-called sport" of Cock-fighting (of which I do not approve) to realise they are selected for their spurs on the hind toe. That's my point in mentioning their rear toes - to distinguish them from this bird.

Wikipedia has some interesting notes about Button-quails.

There is an article in the Wires (Northern Rivers) website which discusses their unusual sex role reversal from the norm, namely the females are more brightly coloured than males, and they "hold and defend their territory" and after the female having laid the eggs, the male takes charge of raising the young. In that regard, they have many similarities to the huge ground-breeding birds, namely Emus and Cassowaries.

Anyway, the point about these photos is that the Button-quail's hind toe has been reduced to a mere "lump" on the foot, so entirely different from the Treecreeper's hind toe (which itself is an extreme adaptation). 

That's what happens when one's ancestors specialise in running around on the ground, in dry country habitats. Your hind toe becomes superfluous. Whereas, if one's ancestors specialise in picking insects from the bark of trees, you develop relatively huge feet and powerful toes. 

Both these birds were photographed last weekend, at Charcoal Tank, near West Wyalong.

No comments: