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Re: Evidence for bat predation on birds

Googling around on stuff like "chiroptera, altitude" gleans 3000m foraging for t. braziliensis... I was mainly wondering about maximum observed reproductive altitude.

That's the figure I found as well, and seems to be what Dann Pigdon came up with.

As usual the most interesting stuff is accidental-- e.g., it seems species richness in birds and bats "declines smoothly" w/ increasing altitude (in the Andes) whereas species richness in local mice does not. Further, the mouse species are more 'discretely zonated' than the volants. Encouraging and unsurprising to a functionalist like myself, who assumes that the gradual change in flight medium density has shaped the bird/bat species profile... in all the ways you might theoretically expect. I hasten to add that as near as I can tell, the authors listed below don't necessarily share my locomotively based assumption. Hard to tell until I get the whole article.

I just took a very quick look through the paper; it's pretty interesting. One thing I note is that the species richness decline isn't really that smooth in birds, though it is in bats. Given the spike around 2500 m for bird diversity, and the high mid-range amplitude, it might be that changes in arboreal habitat are more at work than air density for the species richness change. The evidence for density effects looks (at first glance) to be a bit better for bats than birds. One bit of help would be to include some larger-bodied volant species; they should be less affected by density changes (though they would tend to be less affected by habitat gradients, as well).

This is a little surprising if you just paste it into a black/white cartoon world-- "Highland bat species occupy broader elevational ranges than lowland bat
species, but for both birds and mice, species at intermediate elevations
had the broadest amplitudes."

It is a bit counter-intuitive. Maybe intermediate elevation bird species have wider habitat preferences, or maybe they are adapted to flight at both highlands and lowlands, and just happen to roost at intermediate elevations. Hard to say, but just a couple of ideas to toss out there. Thanks for posting the reference.


--Mike H.