Hi Jill
I know you are now away and may not see this for some time but I have
followed the debate with interest and thanks for including me in the
recent emails. I haven't had a chance to read the Kehoe paper yet but
see it refers to birds breeding in England from June onwards, a little
late in the year perhaps as far as plumage characters are concerned at
the moment (March/April). I have asked my colleagues in SE England to
check the migrating flocks of adult Common Terns for any showing white
foreheads. We see several hundred individuals on their spring migration
in the SE and this peaks about the end of April. From memory, it is
very rare to see any still showing white foreheads in April. Of course
we are talking nominate S.h.hirundo here not S.h.longipennis but I see
you also get the former (at least from ringing recoveries) even if they
are rare.
I read in our birding bible, Handbook of the Birds of Europe, the Middle
East and North Africa; The Birds of the Western Palearctic (BWP) by
Cramp et al that 'hirundo and longipennis grade into each other over a
wide area in central Siberia...proportion of birds with black bills
increasing eastwards..'. BWP also mention the race S.h.tibetana from
'central Asiatic mountains and highlands as dark as longipennis and
length of bill and wing similar, but bill and legs red in summer as
nominate hirundo....'. This may all be irrelevant but shows a degree in
variation between the different races which may complicate things for
you unfortunately. I also read in BWP that birds breeding closer (north
of) to the equator nest earlier and winter closer (north of) to the
equator whereas those breeding further north in Europe (eg Fennoscandia)
winter further south (south of) the equator. So perhaps our early spring
migrants in SE England in full breeding plumage with fully black caps
are British breeders which have come into breeding condition earlier
than those which breed in Scandinavia later. Maybe a similar pattern
occurs in E.Australia with longipennis if they have so far to go to
breed - they may acquire their dark caps later too.
To quote BWP on the plumages of the following (for hirundo):
'In 3rd calendar year, moult cycle similar to adult, but breeding
plumage (if any) obtained later in spring and primary moult either not
arrested or, sometimes, arrested with score other than those found in
adult. Immatures in summer of 3rd calendar year strongly variable: some
similar to 2nd calendar year, showing mainly non-breeding plumage
(though often mixed with some breeding on head), bill often red, no
juvenile outer primaries present, and 3-6 inner primaries new, often
still moulting May-July; others closely similar to adult breeding, but
usually retain part of non-breeding - forehead and underparts mixed with
white and traces of carpal bar present (often showing as scattered dark
feathers only); some similar to adult, but grey of underparts usually
paler. In summer of 4th calendar year, usually similar to adult
breeding, but some have a few all or partly white feathers on lores and
forehead (showing white mottling especially when worn), or dark feathers
of carpal bar partly present; as a few older adults also show these
features, ageing impossible.'
As there has been some mention of plumage colour variation in photos you
might be interested to see the two photos taken of a Sparrowhawk at
Portland (south Dorset coast). Scroll down on the link below to see the
photos taken 2nd April - it is difficult to believe it is the same bird!
http://www.portlandbirdobs.org.uk/aa_latestnews.htm
Cheers
Dave Flumm
Site Manager RSPB Cornwall reserves
Hayle Estuary & Marazion Marsh
Tel. 01736 711682
> The RSPB speaks out for birds and wildlife, tackling the problems that
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