A few days ago Peter Menkhorst explained why the Christmas Island
birds have been dropped from the latest edition of Pizzey and Knight:
"I take a biogeographic view of Australia rather than a political one."
I thought I'd add a few comments on biogeography for anyone that
hasn't read up on the subject. I'm a lay person with a keen interest,
so corrections to anything I get wrong are very welcome.
First off, you don't need to know anything about biogeography to enjoy
birding and people are free to ignore biogeography for their lists.
However, I've found that understanding a bit about biogeography and
the processes contributing to speciation makes birding far more
fascinating. This should perhaps more true for Australian birders than
for birders starting anywhere else. Anyone who has birded outside of
the country must have wondered why the birds are so different from
here in most areas. Huge otherwise-global families (such as the family
including woodpeckers and barbets) don't have a single member in our
region. Why? Australia has a staggering variety of honey-eaters with
similar habits and appearances. Why are there so many in seemingly
similar country?
According to what I understand, isolation and time are primary engines
of speciation. That makes islands (of whatever kind) of particular
interest. However, not all islands are created equal. Leaving aside
land-locked islands such as mountain tops and other fragmented habitat
types, there are at least two very different types of islands in the
ocean: continental islands and oceanic islands. They've got totally
different natural histories. "Oceanic" islands are islands that are
and never were part of a mainland, such as the volcanic islands of the
Pacific. "Continental" islands are islands that have been part of a
mainland either originally or recurrently, such as our near-to-shore
islands. From knowing the type of island, its size, and (in the case
of continental islands) the frequency of reconnections to the
mainland, you can make a lot of predictions about the diversity of the
avifauna and its degree of endemism.
So, consider some oceanic islands:
-- Everything in the central and eastern Pacific, including all of
Polynesia and, I believe, all of Micronesia, and much of Melanesia.
-- The Seychelles in the Indian Ocean. The world's only granitic
oceanic islands, as far as I know.
-- Reunion and Mauritius (home of the Dodo) in the Indian Ocean.
-- Ascension and other isolated islands in the Atlantic.
-- New Zealand
-- Christmas Island
-- The Galapagos
-- The Falklands
The only creates to colonize these islands (prior to human contact)
either swam, flew, or drifted there. Therefore, these islands (befeore
human contact) had a lot of common features:
-- No mammals or close to no mammals, short of bats.
-- No reptiles and amphibians that don't have an egg-laying style that
allows for drift delivery through salt water. (You get a few native
geckos throughout the Pacific, for example.)
-- Birds with a staggering degree of endemism. Land bird endemism may
easily reach 90-100% of the native birds.
-- A lot of flightless birds [virtually all extinct today] as the
'expense' of flight is no longer worth it without land-based
predators.
-- Huge sea bird colonies (again, no land predators).
-- A land bird list with an unusually high representation from
specific families. Namely, good dispersers: owls, parrots, pigeons,
and coot-like-birds.
-- A remarkable degree of fearlessness when exposed to humans. Darwin
famously killed a hawk in the Galapagos by hitting it with his hat.
(Australia, by the way, has birds with greater fearlessness of humans
than any other mainland, as far as I know. Just try seeing parrots
anywhere else!)
It's hard to say exactly what the situation was in these islands
pre-contact as, in the case of the Pacific, the Polynesians pretty
well swept through each eating everything they could catch until
nothing was left. In Hawaii, for example, they keep turning up new
sub-fossil remains of birds that were wiped out by Polynesian
colonists. I'm not meaning to be critical of the Polynesians, by the
way, they just got their first. Seeing reconstructions of Polynesian
sailing craft can only leave you impressed that they colonized such a
vast ocean. Anyway, even from the fragmented remains of the native
birds in Polynesia, you see a staggering degree of endemism.
What about continental islands? (I think all of these are continental,
but I've spent much less time on continental islands)
-- The Channel Islands off of southern California (there's an endemic
Jay, part of the crow family.)
-- The Torres Strait Islands
-- Kangaroo Island
-- The Bass Straits Islands
-- Tasmania
Since these islands were originally part of a larger land mass, you
see a totally different natural history playing out. Now creatures
could colonize by walking. Therefore:
-- You get a bunch of mammals, often with some degree of endemism. (It
depends on how long they were isolated, such as in Madagascar, or what
got wiped out on the mainland...Tasmania, of course, is a refuge from
some species that used to exist on the mainland here.)
-- Birds aren't as fearless.
-- A lower rate of endemism on a species level and a *much* lower rate
of endemism on a higher level, such as family/sub-family/order.
[Granted that the higher order classes are largely conceptul.]
-- Sea-bird colonies have to be isolated on sea stacks and such.
Biogegraphically, the two types of islands are *fundamentally*
different. Oceanic Islands each have a unique natural history since
they don't have any intimate, recurrent, or ongoing connections to a
mainland. Scientifically, it makes sense to record which species are
seen on *specific* island. Taking the main Hawaiian chain, the Elapaio
occurs on Oahu, Kauai, and Hawaii. This is a charming little bird that
looks and acts pretty much exactly like a Fantail which is, I believe,
classed as a Monarch. Recently, it was split into three different
species based on DNA analysis. Even though the island in the main
chain are only a few hundred kilometers apart, it was plenty to create
the isolation necessary for speciation. (Some birds wont fly across
roads, let alone ocean channels.)
By the way, birders from the USA are as bloodthirsty a lot of listers
as you could hope not to meet. All the same, they don't include the
Hawaiian island birds on their lists because the islands are so
removed from the mainland. Hawaii is the 50th US state, so there's no
question it's politically part off the US.
So, for Christmas Island, scientifically I'd guess it makes sense to
group it with....Christmas Island. It isn't that far from Java by
plane but its animals don't seem to have a particularly close
connection with the Indonesian archipelago. Kangaroo Island, to take a
counter-example, is plainly closely (and recently) connected to the
Australian mainland.
Listing isn't towards any scientific purpose so it makes no
substantive difference that political-bounded lists make no particular
sense scientifically. So, if it pleases people to lump birds seen in
CI with their Australian mainland lists, what's the harm? My favorite
idea on this point came up on this list as a question some time ago:
why not include birds seen in Australian embassies around the world? I
love that idea ;-) By the same logic, the UK has about eight regularly
breeding penguin species.
By the way, anyone wanting to see a lot of endemics should look for
any of the following:
-- A large, isolated island. (Australia, Madagascar...)
-- A large island with lots of different elevations to create
fragmented habitats (New Guinea, Borneo....)
-- A very isolated island/archipelago. (Hawaii, Galapagos...)
-- An archipelago that, due to changes in sea level, allows islands to
periodically reconnect. (Philippines, Indonesia...) This gives
isolated populations enough time to speciate and then recolonize when
the land bridge forms again.
-- A continent where changes in temperatures/glaciers allow
mountain-tops and other fragmented "islands" to periodically
reconnect. (South America.) As a mundane example, North America has
something like seven similar-looking species of Chickadee (small
American tits) with virtually non-overlapping ranges. Ice ages create
'islands' that can last long enough for isolated populations to
speciate through normal drift.
Biogeography is a great subject because much of it is accessible to
lay people and it can really enhance your appreciation of what you're
seeing. Even within Australia, there are huge sections of the country
that are functioning ecologically as islands, such as the southwest.
David Quammen has written a great overview of the subject named "The
Call of the Dodo". It's a great read. Wallace's Island Life pretty
well kicked things off. It's still readable but he's not as great a
writer as Darwin. Still, it covers a lot of areas to our north, which
makes it a bit interesting in that respect. Since "Dodo" a quite
significant book has been added to the conversation "The Birds of
Northern Melanesia" by the late Ernst Mayr, Jared Diamond, with
outstanding plates by Doug Pratt. Pratt is no mean island biogegrapher
himself, being the man behind "Birds of Hawaii and the Tropical
Pacific." Not a simple field guide, the Mayr-Diamond book seeks to lay
out the mechanisms of speciation underlying the full avifauna of an
archipelago. No one has every done such a thing before, they claim,
for any group of animals. Their study region has had less human
impacts than most, making it an ideal subject. The book may be more
accessible to Australians than other English-speaking birders because
the bird families are all familiar.
---------------------------------------------
David Adams
Wallaga Lake 2546 NSW
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