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Birds Had To Relearn Flight After Meteor Wiped Out Dinosaurs, Fossil Records Suggest (theguardian.com)
An anonymous reader quotes a report from The Guardian: Birds had to rediscover flight after the meteor strike that killed off the dinosaurs, scientists say. The cataclysm 66 million years ago not only wiped out Tyrannosaurus rex and ground-dwelling dinosaur species, but also flying birds, a detailed survey of the fossil record suggests. As forests burned around the world, the only birds to survive were flightless emu-like species that lived on the ground. The six to nine-mile-wide meteor struck the Earth off the coast of Mexico, releasing a million times more energy than the largest atomic bomb. Hot debris raining from the sky is thought to have triggered global wildfires immediately after the impact. It took hundreds or even thousands of years for the world's forests of palms and pines to recover. Fossil records from New Zealand, Japan, Europe and North America, all show evidence of mass deforestation. They also reveal that birds surviving the end of the Cretaceous period had long sturdy legs made for living on the ground. They resembled emus and kiwis, said the researchers whose findings are reported in the journal Current Biology.
It's interesting that flightless birds had a pretty strong reign during the early recovery phases. They were often the dominant hunters of the time.
It's often speculated that mammals eventually replaced those giant flightless birds as the alpha hunters not because mammals are more powerful than big birds, but rather because mammals learned to better leverage pack hunting: social coordination. Otherwise, this era would have resembled Dinosaurs 2.0, with 40-foot birds: Sqaaawwwk!! BOOOM
Table-ized A.I.
Both the article and the summary but not the actual paper make the claim that the only birds to survive were flightless. The actual paper talks about the demise of arboreal species. This makes sense as it is difficult for a tree-dwelling species to survive if the trees have gone. It does not follow that the survivors were necessarily flightless. Today most ground-dwelling species retain the ability to fly. And many of these have long, sturdy legs. Given that these kinds of birds don't tend to fly much, it is reasonable that many of these would adapt to a purely flightless lifestyle in the absence of predation. It does not follow that birds had to learn to fly all over again. Even if it took hundreds to thousands of years for the forests to recover, there should still be populations that retain flight ability allowing them to radiate back into the trees quickly.