Philip Veerman wrote:
>I also have a theory that all passerines fly with their legs (actually
their feet) flexed >forward (pointing towards the chest) at the ankle joint,
whereas non-passerines fly with >their legs (actually their feet) held
straight backward (pointing towards the tail) at the >ankle joint. It is my
theory but I have never seen any exceptions to this. Does anyone >out there
have other ideas?
Yes. If you watch closely, many seabirds can hold their feet forward under
their chests, as you describe for passerines. I have seen this many times,
but it was first pointed out to me by David Eades. My impression is that
tube-noses typically only hold their feet forward when they are in free
flight, planning to fly for some distance, but they typically hold them
backwards when they are flying short distances or manoevring, so you are
much more likely to see them holding them back than forward. For example, if
they come in to approach a ship, they often lower their legs as they
manoevre in, and then when they tuck them up it tends to be backwards.
Obviously, this has implications for identification, when foot projection is
sometimes an important feature! It could also affect other features - for
example the femoral tract is often visible from above, but presumably
wouldn't be if the feet were tucked forward. This might explain some of the
variability in features like the extent of white showing at the base of the
uppertail in various shearwaters.
Chris Corben
Birding-Aus is on the Web at
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