> What's the defence against a swarm of drones apart from jamming them?

It's the same as the defense against a large air raid, except the targets are a little different:

+ Size of targets + Speed of targets + Altitude of targets

Or what's the defense for high end autonomous drones that doesn't even need operator for terminal guidance. Getting drones to terrain hug also circumvents alot of interception methods on the horizon.

EMP, strong winds, netting, lasers, and trained hawks

Counter-drone or other ballistic interception?