While flying his quadcopter earlier this week in Cambridge, Massachusetts, Christopher Schmidt experienced firsthand the problem that confronts drone-delivery startups: raptors don't like sharing their airspace.

What happened to Schmidt is a portent of what could happen to that package you're waiting for if companies like Amazon begin flying the not-so-friendly skies.

As bird expert Nicholas Lund has written in Slate:

Birds already cause a lot of problems for other things in the airspace. The FAA has tracked more than 121,000 instances of bird-aircraft collisions since 1990. These are accidental; the birds—most frequently gulls or pigeons, or in the case of the plane that landed on the Hudson River, Canada geese—are spooked off a runway during takeoff or landing.

The difference for Amazon's drones is that the birds will be chasing them. Unseen to us, the skies are checkered with fiercely defended bird territories. Open-country raptors—hawks, eagles, kites, harriers, etc.—don't take kindly to interlopers on their hunting grounds, and frequently chase, dive-bomb, and take talons to intruders. The confrontations can be even more violent during nesting season when vulnerable chicks are potential prey.

Won't birds know that Amazon's drones aren't really threats, though? Nope. To a bird, a big flying thing is a big flying potential threat.