After the asteroid hit, beaks were thought to be an advantage:
By the end of the Cretaceous, beaked birds were already eating a much more varied diet than their toothed relatives. These birds weren’t specialized on insects or other animal food, and so they were able to pluck up hard food items like seeds and nuts. And in the aftermath of the extinction, when animal life was severely cut back, those hard, persistent little morsels got beaked birds through the hard times. Beaked birds were able to feed on the seeds of the destroyed forests and wait out the decades until vegetation began to return.
Not that beaks guaranteed survival of the impact event. The duck-like bird Vegavis lived at the end of the Cretaceous and had a beak, yet there’s no indication that this avian survived. “Just having a beak was not enough,” Tucker says. Rather, it’s that birds with beaks and powerful gizzards capable of crushing tough seeds had an unexpected advantage that increased their chances of survival. Riley Black, “Why Birds Survived, and Dinosaurs Went Extinct, After an Asteroid Hit Earth” at Smithsonian Magazine
Interesting hypothesis. It would be thought-provoking to read a list of all the hypotheses as to why some life forms survived and others didn’t and look for patterns.