What I would like to know is, is there anything special about the birds
that don't migrate. In the early 1980s, we caught and banded about 150
Grey Fantails, all but some 12 to 18 (excuse the memory - obnubilated by
age and alcohol) in spring/summer/autumn. All but one of the winter birds
were aged as first year birds and it's not impossible that the odd one out
was a young bird too. But what were these young birds? Were they the
total surviving young of the local patch (if so, I would have expected to
have caught more), were they local young from late broods who couldn't get
in condition in time to migrate (my favoured option), or did they come from
somewhere else and, if so, whence and why didn't they behave the same as
the other birds from the somewhere else (seems unlikely)? An incidental
but possibly relevant fact is that, in many bush bird species, young from
later broods often moult later, sometimes in the following season, than
those from earlier broods.
Does anybody have any ideas or relevant facts or, even better,
publications? When is the RAOU going to publish the ABC results?