There are birds heavier than these, and planes usually handle bird strikes quite well.

Actually, Relatively small birds have been known to penetrate the windshield of a Cessna and injure the pilot or even wreck the engine of a single engine of a jet like a BAE Hawk.

See video of a Canadian CT-155 Hawk (Not F-16 as titled) https://www.youtube.com/watch?v=zN_Zl64OQEw

For an airliner like an Airbus A320, a small bird can damage the engine fan blades and require an expensive repair. If the bird goes through the core even minor damage becomes very expensive to fix.

I don't think it's so much the weight but the material.

Sharp metal and plastic edges are way more likely to shatter glass than a puny piece of flesh.

These can't be flown at 15,000 feet legally (in the US) without a special FAA civilian UAS license. Without such a license you can fly them under 400 feet using the model aircraft rules but going over 400 feet is not allowed sans license.

DJI's Phantom quadcopters (with newest firmware) enforce the 400 foot ceiling in software, not sure what their plans are with this one since it is being marketed as much more pro-sumer than than the Phantom line, but if Joe Schmoe Parkflyer flies one of these above 400 feet he is violating FAA regulations and theoretically could be charged large fines currently.

Regarding the 400ft limit in software: Has it got some sort of radar altimeter or does it just assume the launch point is the ground and will not travel 400ft above that?

It has GPS and knows when it is getting into restricted airspace. In addition to Lat and Long, GPS also gives altitude above sea level. You couldn't launch a Phantom from the top of a highrise and think you are cheating the system.

Are you sure about that? I mean, it still needs to know the starting altitude to calculate the difference. Unless this limit is above the sea level which I somehow doubt. As an engineer, I'm interested how did they manage to solve this problem.

Since the Phantom's flight controller is closed source, this is speculation but I assume it calculates it based on the altitude delta from "home".

When you turn the Phantom on one of the first things it does is tries to get a GPS lock on its current position which it will use as the "home" point. This is a pretty important piece of data for the device to have (and the bright LEDs on the arms will light up red until it has it, warning you that taking off is dangerous) because if it goes into "return to home" failsafe for any reason (loss of connection to the controller, battery low situation, etc) the device will attempt to fly itself to that position (after first ascending to a programmable return-to-home altitude if needed to minimize risk of hitting obstacles like trees or houses).

The controller on the Phantoms also has a barometer which can be used for (relative) altitude change readings. I have no idea if it uses that at all in the 400 foot ceiling calculations.

It is extremely doubtful that the Phantom carries any sort of WGS 84 to local height mapping because that is a ridiculous amount of data (even at a fairly low resolution) to carry for the entire globe, and it has no link to any kind of lookup service for that, and if you based the height on sea level that would make the device pretty worthless in many places (eg. Denver which is more than 13 times higher than 400 feet above sea level at ground level).