also we're missing something with Henicorhina. Remarkable how leucophrys here 'drops off' at about 1400masl with no obvious change in anything. Then at about 1100masl leucosticta occurs around streambeds etc. That sp pair remains puzzling to me, where in other sites they abut..

..mexicanus is v.common here and terri density is high which probably contributes. Some frantzii territories are in bamboo thickets etc.
Could also relate to nest choice (mexicanus usually in the back of a bromeliad, which themselves change with increasing elevation, species i think + densities)

thats a v good question..
My hunch for Catharus is that its something about structural complexity and how they use territories. mexicanus is very prominent and vigilant - sings constantly to defend territory. frantzii is much more skulky, often on the forest floor so could be a behavioural thing..

cc/! @benjaminfreeman.bsky.social @sjportugal.bsky.social @josephtobias.bsky.social

Theres an urgent need to understand these mechanisms to make accurate projections of species responses to CC in tropical hyperdiverse regions.
..aside from the inherent interest in species ranges which naturalists of all shapes interact with daily (and that we have so much still to learn about!)

..but if not physiology (tracking thermal conditions that shift upslope), then why?
the answer is likely in complex relationships between competition&habitat which itself shifts at variables rates..
much to learn here in these combos -
www.science.org/doi/full/10....
www.pnas.org/doi/abs/10.1...

Why do tests like this matter?!
Understanding elevational ranges, allows us to understand elevational changes..

We know that tropical montane birds are shifting their ranges upslope.. (e.g. www.pnas.org/doi/abs/10.1...)

The answer appears to lie in habitat preference -

lower elevation (dominant) Catharus mexicanus, preferentially chooses open broadleaf forest and avoids fern dominated forest, excluding the higher elevation (subordinate) C.frantzii to habitats it doesn't want to occupy..

For Nightingale-Thrushes, an interaction between competition and habitat shape their elevational ranges.

The interaction between them is asymmetric (the norm in birds) - with the lower elevation species, dominant over its higher elevation counterpart.

So WHY NOT go higher up, if you can?

..with that info, we can test each hypothesis..
The upshot here is that thermal physiology has no bearing on where species CAN physically live (2x BMR suggested as the physiological 'ceiling' for species) - our species live comfortably within this.
So if not physiology, then what?

Then..
3. Measuring thermal physiology - what energetic cost to cold exposure does a species incur at different elevations?
4. Measuring microhabitat at every survey site
5. Experimentally testing how competition looks between species onlinelibrary.wiley.com/doi/full/10....

So i wanted to get mechanistic, and measure each of these variables on species and test them in unison, which meant:
1. Establishing abundance patterns across elevation by lots of point counts
2. Characterising the thermal environment birds experience across elevation..

3 key explanations-
1. Physiology (its too cold/hot at different elevations for a species to persist)
2. Competition between species limits distribution
3. Habitat (an ecological preference/specialism limits the range)..

There is nice work on each, but nothing pulling them together...

It was (still is..) wild to me that you can hike through the range edges of species.
Higher up = common, lower down = absent (or vice versa)

But what causes this?!
and why do species occur where they do?!
our understanding of what limits species ranges is still remarkably incomplete..

I especially like your wand there 🦎🧙‍♀️

Love it- nice one!