It is often considered that Christmas Island is strictly in the Oriental
region and looking at its position about 380 km S of the west tip of
Java it is easy to see why. A closer look at the 23 resident birds
though may reveal a different perspective.
Red-footed and Brown Booby, Greater and Lesser Frigatebird, Red-tailed
Tropicbird, White-faced Heron, Eastern Reef Egret, Nankeen Kestrel,
Common Noddy, Emerald Dove all have breeding populations in Australia.
The Christmas Island Hawk Owl and Variable Goshawk have been lumped in
historically with Moluccan Hawk-Owl and Brown Goshawk, both of which are
founders from the Australasian realm. The Linchi Swiftlet is closely
related to the Glossy Swiftlet widely distributed in New Guinea. The
Christmas Island Imperial Pigeon is a representative of the genus Ducula
that reaches its greatest diversity in Australasia. Island Thrush had
populations on Lord Howe and Norfolk Island that became extinct in
recent times although the species has healthy populations in New Guinea.
Tree Sparrow is introduced into both Australia and Christmas Island. Red
Junglefowl (or more strictly Feral Chicken) is introduced into both
Christmas Island and Australia. Abbott's Booby and Christmas
Frigatebird wander to Australian territory on occasions and White-tailed
Tropicbird is a frequent visitor. So this leaves us with the introduced
Java Sparrow, colonising White-breasted Waterhen and endemic Christmas
Island White-eye. The latter is also of a genus Zosterops that is very
well represented in Australasia.
So it would appear Christmas Island has been well colonised by taxa of
both definitively Australian and Australasian origin. A quick analysis
of a slightly out of date list of the vagrants-irregular visitors of a
list of 104 produced only 11 that have not made it to mainland
Australia. Many of the vagrants to CI are clearly Australian birds like
Black-tailed Native-hen, Horsfield's Bronze-cuckoo and Pied Heron. So
Christmas Island way out in the middle of the Indian Ocean well south of
Indonesia is a remarkable location at the cross roads of Australasian
and Oriental birds.
Cheers
Dion
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