How birds barely survived the K-Pg extinction event

Crown birds
“include the most recent common ancestor of all modern birds, and all of its extant or extinct descendants.”

Here
in the large reptile tree (LRT, 2017 taxa) the most recent common ancestor of all modern birds is Megapodius, the scrubfowl (Figs. 1, 2). That means if you have a flock of Megapodius living at the K-T boundary, you can evolve all the birds that appear in the post-Cretaceous era.

…which is exactly where you want to be according toWired.com
who created a “You might survive” zone (Fig. 4). This happens to more-or-less coincide with the known range of Megapodius and its fossil taxa. The islands were surrounded by moderating oceans, so neither fire nor freeze would have been lethal.

Whatever helped scrubfowl adults survive the K-T event
goes double for their eggs, which are buried under mounds of soil and vegetation created by their hopeful parents. Scrubfowl hatch out ready to take care of themselves, distinct from more derived birds that need parental care.

Perhaps the first post K-T generation of scrubfowl
had to take care of themselves in a world where, for a week or two, there were no dinosaurs or birds anywhere on the planet… and then, one-by-one little scrubfowl hatched to repopulate the planet, evolving over millions of years to fill every niche.

References
Claeys P 2007. Impact events and the evolution of the Earth. Advances in Astrobiology and Biogeophysics. In: Lectures in Astrobiology DOI:10.1007/978-3-540-33693-8_9

https://www.wired.com/story/how-to-survive-a-killer-asteroid/

https://www.princeton.edu/news/2011/10/19/impact-study-princeton-model-shows-fallout-giant-meteorite-strike