array9

Bird's upright stance

When standing on the ground or on a branch of a tree, a bird makes an angle to the horizontal.  Sometimes birds are very upright, and sometimes rather low.

It occurs to me that although this angle can be varied by the individual bird, it likely takes a little effort to do so, and that there is a stable position that birds will tend towards.  I would guess that some of the joints effectively lock in such a position and this reduces the energy requirements.

My hypothesis is that birds that send a lot of time on the ground feeding will tend to be those that are more horizontal.  Their bills will be nearer the ground, and their tails off the ground.  Blackbirds and thrushes for instance.

Birds that roost on the ground would also tend to be horizontal ( eg seagulls )

But I have no good reason for what tree roosting or feeding birds should do.  I think that they are more upright, but I don't know why.

 Fly catching birds might get a better view of insects that are at the same level as them, and therefore expend less energy catching them, avoiding a climb before or after the catch?

Upright birds might get a better view backwards at predators gliding in attack?

I doubt if it has much to do with the centre of gravity, since I would expect this to be above the ankle whatever the position of the body.

All ornithologists make use of the stance to identify birds as they are good reliable indicators.  I am just interested in getting an understanding as why they are as they are.

martinW