Thanks for
passing this on Mike. I agree with your ID as a Great Frigatebird.
Firstly
though, frigatebirds disperse widely. Ascension breeds in the Tropical
Atlantic, about 6,000 km due west of the coast of Tanzania in the IO. It is a
vagrant even to the west coast of Africa, and from there a bird would need to
cross tropical Africa or round the Cape to get to Tanzania. It is possible I
suppose. Magnificent breeds in the Cape Verde, not much further away, 7,500 km
wnw. The same deal applies. Neither has been recorded in the Indian Ocean.
Christmas Frigate breeds only on Christmas I in the eastern IO, about 7,300 km
east of Tanzania, but there is only tropical ocean in between, no deserts.
Christmas has been recorded in Kenya in the 1960s (not officially accepted by
Kenya's rarities committee, but Clive Mann's photos convinced me and Peter
Harrison who originally identified the bird for Clive). On the other hand, both
Great and Lesser breed from east to west in the Tropical IO and are regular
along the tropical east coast of Africa, so weight of probability is with one
of those two. However, all 5 deserve to be considered. I only know Great,
Lesser and Christmas well. Steve Howell (1994) dealt with the separation of
Great and Magnificent, and I dealt with Christmas, Great and Lesser (James
2004), so Ascension is the only one not treated in a detailed ID article.
Frigatebird
ID is complicated, so be warned, the following will bore some people to death.
The white
head indicates it is young but not fresh juvenile plumage. No adult
frigatebirds have white heads, not even the pale morph female Ascension (beware
of label errors on web photos). The 'white' head feathers are worn, abraded and
bleached buff feathers of juvenile plumage (Magnificent and Ascension have
actual white feathers, and the other 3 bleach to white routinely even before
they fledge). The unique brown underparts plumages of Ascension Frigates occur
in adult plumages. Breast bands of juveniles of some species have some dark
brown mixed with the black, and this is certainly typical of Greater and
Lesser, so that in itself is no reason to suspect Ascension.
The breast
band is narrower in the centre, which creates a rounded anterior edge to the
white belly patch, effectively making the belly patch an oval or egg-shape (if
you ignore the spurs for a moment). That is the typical shape of a juvenile
Great. Lesser has a straight rear margin to the breast band, so a straight
anterior
margin to the white belly patch, which effectively makes the belly patch more
triangular in shape. Photos of juv Ascension on the web appear to show a
parallel-sided breast band so a straight anterior edge to the belly patch, but
a rounded rear end of the belly patch making it an elongated semi-circular
shape. Magnificent has the breast-band narrow and set well back, and sharply
tapering to the centre (usually broken across the centre) so the belly patch is
small and diamond shaped (Howelll 1994). Christmas has a hexagonal shape to the
belly patch with angles rather than curves. The oval belly patch favours Great.
The spurs
are restricted to the flanks or perhaps just reach the underwing, as Mike
observed. They are also blunt-tipped. These eliminate Lesser which has tapering,
pointed spurs that extend well onto to the underwing. On Lesser the spurs
originate from the front corners of the triangular belly patch. About 1/3 of
juvenile Great (although worn this bird still has juvenile body plumage) have
spurs
that originate off the side of the belly patch and extend only onto the flanks,
just like this bird. This bird is admittedly at the extreme end of Great for
development of spurs, in my experience. The spurs of Christmas extend well out
onto the underwing. Juv Ascension apparently has a lot of white on the flanks,
but in the few photos I've seen it tends to be broader and more of a flank patch
than a narrow spur, though the shape is not consistent. The spurs of
Magnificent are small, narrow and tapered (Howelll 1994).
The bill of
the Tanzania bird is clearly pink. When the adult females have blue bills their
juveniles have pale blue-grey rather than pale pink bills. Adult female
Ascension
and Magnificent have blue bills and the juvs have grey ones. In Christmas the
adult female bill is bright pink and the juv is pink. In Lesser the female has
pink-billed and blue-billed morphs. In Great the female bill can be pink or
blue depending on location. Bill colour rules out Ascension and Magnificent but
not Great, Christmas or Lesser.
The bill is
probably too short for Christmas. The wings are too narrow at the base and the
humerals not sufficiently elongate and bulky for Christmas.
I think
every species can be eliminated on several points, except for Great. It looks
absolutely
fine for a worn juvenile Great of the Indian Ocean susbspecies aldabrensis (and
probably female due to
size and pink bill).
Howell, S. N. G. (1994) Magnificent and Great Frigatebirds in
the Eastern Pacific: A new look at an old problem. Birding Dec. 1994:
400–415.
James, D.J. (2004). Identification of Christmas Island,
Great and Lesser Frigatebirds. BirdingAsia 1: 22-38.
PS Steve, I can provide James 2004 for your drop box if you want
Cheers,
David James
Sydney
==============================
>
> My friends on the Tanzanian equivalent of birding-aus are currently
> wrestling with the identification of a frigatebird that has been
> frequenting some of the nicer beach-side suburbs of Dar es Salaam. They
> have asked me to post some photos on birding-aus for the Australian experts
> to examine.
>
> So there are four photos here:
>
> https://www.dropbox.com/sh/bec5nxr4ul166fz/90IJhl3pfU
>
> I'll pass on any opinions that emerge.
>
> Cheers
> Steve
===============================
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
http://birding-aus.org
===============================
|
