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Hi Chris,
I confess my comment on tail shape was a bit
casual, so I'll elaborate. Generally speaking I would be surprised if
tail-feather tip shape differs substantially if at all between Sp.hawk and Gos.
and is not the reason for a square tail in Sparrowhawk. I agree with you
that square/round tail tip is a result of the relative lengths of outer verses
inner rectrices. The individual in question has a roughly parallel sided foulded
tail eg. the feather shafts are parallel. With both Gos. and Sp.hawk the
individual tail feathers from 1 to 6 are approx. the same width, what does
change from 1 through to 6 is the tip profile shape. After being parallel sided
for most of its length with a central shaft( both veins of equal width ),T1
eventually tapers to a rounded tip the sides therefore curve for the last 1/4 of
it's length. The shaft of T6 on the other does not run centrally which results
in the outer vein being substantially narrower than the inner and therefore the
outside edge looking straight for the entire length. This is what makes a tail
look angular when all the tail feathers are roughly the same length. A same
tail-feather length tail would not look as square if all of the feathers T1 to
T6 where the same shape as T1. You don't see an angled corner in Gos. because T6
inwards get longer incrementally but if you left it's T6 intact and trimmed its
other tail feathers to the same length it would appear just as angular as a
Sp.hawk.
There have been a number of Sparrowhawks around
Heidelberg in recent years and when I have seen them straight tailed like the
bird photographed this is when the notch can be most apparrent. After saying
Sparrowhawk has tail-feathers of equal length I am now going to contradict
myself slightly by saying that is not quite the case. T1 often appears a
fraction shorter, maybe this is where the apparrent notch comes
from.
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