What is birds’ biggest threat since asteroid?

The threat paleontologists emphasize

A new book discussion with paleontologist Steve Brusatte frames a modern challenge for birds as potentially their “greatest existential threat” since the asteroid event that wiped out non-avian dinosaurs. The core idea is that, while birds survived the ancient mass extinction, they are now confronting a different scale of pressure from environmental change.

Why this comparison gets made

Brusatte’s perspective ties the long arc of bird evolution—from Jurassic survivorship to present-day diversification—to what makes that lineage vulnerable today. Birds are the sole surviving dinosaur lineage, so the stakes are inherently high: what endangers birds is not just a subset of wildlife, but the living representatives of a deep evolutionary history.

What matters for conservation

The excerpt provided doesn’t spell out the exact modern mechanism behind the “existential threat” phrasing. Still, the comparison signals why the book is structured around survival and resilience: it’s meant to highlight that the factors that allowed birds to persist for tens of millions of years are not automatically protecting them now.

At a practical level, the message is that current threats are severe enough to warrant urgency from conservation biology and policy—because losing birds would mean losing an entire branch of Earth’s evolutionary story.

What’s not specified

No detailed causes, study findings, or quantified risk estimates are included in the story text you supplied. To understand the “why” in full, you’d need the book’s specific discussion of the threat’s drivers.