[ArkanExplorer]

Could high levels of CO2 be the cause?

CO2 at 800ppm has a huge impact on mouse lungs:

https://news.ycombinator.com/item?id=27721892

Could lower levels (400s ppm) have an impact on other parts of animals?

[jbotz]

Unlikely. Remember that birds are dinosaurs... they spent a significant portion of their evolution at a time when there was a lot more CO2 in the atmosphere. Bird's lungs are much more efficient than mammalian lungs, which is why some birds can fly up to altitudes at which humans would lose consciousness if they weren't in a pressurized airplane cabin! With that and their mobility, birds (at least a few species) are good candidates for surviving the 6th great extinction... given that some are also very intelligent, maybe dinos will get another shot at inheriting the earth after all! ;-)

[hoppyhoppy2]

The article says they've been seeing this illness spread since April. If it was caused by rising CO2 levels I'd expect its appearance to be much less sudden.