Just making a further brief comment on the field observation for benefit of future reference and research. Nest was in a completely dead tree. Chicks were observed multiple times experiencing heat stress. This was mitigated to some extent by standing at the shelf-like nest entrance, which fortuitously allowed such behaviour. The stronger chick stood on the shelf to the right of image, in a much cooler, ventilated position, and was not panting. The weaker chick stood at nest entrance and was constantly panting (as seen in this image). Both chicks survived and fledged, one day apart from eachother. Broader implication is that depending on the nest, chicks can indeed die from heat stress.