Birds and Wallace’s Line

Continuing the discussion from Herman Mays Accuses Joshua Swamidass:

I’m pretty interested in Wallace’s line. What do you find in the distribution of birds here?

Observers might need a quick refresher on what exactly Wallace’s line actually is.


It’s a biogeographical break in the Indonesian archipelago that separates Asia from Australasia (New Guinea/Australia) named after Alfred Russel Wallace. It’s created by very deep water channels running through the archipelago and is why there are no tigers and rhinos in Australia and no kangaroos in Asia.

It also affects the distribution of birds. Some have managed to cross it (pigeons and cockatoos for example). Most others (birds of paradise for example) not so much.


IIRC there are (at least) two lines - Wallace’s and Weber’s - for different types of fauna.


I forgot about Weber.

Can you link some papers please?


Wallace, Alfred Russel (1863). “On the Physical Geography of the Malay Archipelago”. Royal Geographical Society. 7: 205–212.


If I recall, oscine passerines have escaped from Australasia (i.e. crossed Wallace’s line), based on phylogeny, only three times in earth history. Though a few have made it back across the line also.

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How many individuals have to cross in order to establish a sustainable population?

Wallace’s Malay Archipelago itself is an interesting read if you want to go old school. Just imagine the collecting permit issues he would have today!

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No idea. The “three times” are of course not individual birds but three instances in which enough birds crossed of one species to establish a clade that survived until the present day.


Yep that indeed appears to be the case.

I believe this is the one: Barker F.K., Cibois A., Schikler P., Feinstein J., Cracraft J. Phylogeny and diversification of the largest avian radiation. Proceedings of the National Academy of Sciences 2004; 101:11040-11045.

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Jon Fjeldså, Les Christitis, and Per Ericsson have a new book out on the evolution of the passerines that I need.

Teach me. What is a passarine?

The perching birds. About half of all avian species are passerines.

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Yeah it’s a stochastic thing. The more immigrants there are the more likely a new population is founded. Lots of these avian taxa that are good at speciating on oceanic islands aren’t solitary.

Member of the order Passeriformes, or perching birds, which is a bit over half of all extant bird species. Oscines is a suborder that’s about 2/3 of passerines. The evidence is quite good that it originated in Australia.

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It’s an order of birds, the passeriformes. That cardinal and finch and wren at your feeder are all passerines as is the robin pulling up worms in the yard and the crows flying overhead. They have some synapomorphies in regards to the anatomy of their feet and the palette among other things but they are a VERY diverse group.

What are the other orders of birds?

There’s like 40 or so. Off the top of my head. This is something where Wikipedia can give you a decent answer.