As I understand it, the ejecta resulting from the K-T impact (also known as the end-Cretaceous or Cretaceous-Tertiary extinction event) re-entered the atmosphere all over the world; the heat from friction with the atmosphere raised the air temperature to a few hundred degrees C. All organisms all around the World were incinerated, except those that could bury underground or move into water.Now birds don't bury underground, nor do they bury their eggs. So, how come birds didn't go extinct?
To clarify, I'm not considering the longer term cooling effect (which was in turn followed by a longer term warming effect due the CO2 dumped in the atmosphere). What happened just after the impact was that a sizable fraction of the entire volume involved on the collision would be on ballistic trajectories. Most of these would fall back to Earth, while a small fraction would escape Earth's gravity. Now, these ejecta actually contain a significant fraction of the total energy of the impact and almost all of that in then dissipated as heat when they re-enter the atmosphere. This leads to shock heating of the atmosphere to at least a few hundred degrees celcius, but much higher temperatures are also possible, see also this article.