Although it must be determined by experiment I would guess anything in front of the jet intakes would severely affect engine performance.

I agree with sand, jet fuel is really expensive, having anything in front of it will cause a drop in efficiency. Even a 1% drop translates into 100's of millions of $ for the airline industry.

A similar idea was proposed, something like a grill in front of the turbine blades, which can be pulled back after takeoff. The problem again however is that a very large quantity of fuel is burned during take off to create the lift, so lots of losses if we put something in front of the jet engine.

I suppose a sound based approach is better.

The US Defense Department is developing a narrow beam microwave projector to stimulate pain in crowd control. If this could be projected in front of an airliner it might cause birds to quickly scatter away from the beam without interfering with engine function.