It is possible to 'hear' microwaves, so even if weather radar doesn't put birds away, a device that repels birds might be possible.
http://en.wikipedia.org/wiki/Microwave_auditory_effect
Microwave auditory effect
From Wikipedia, the free encyclopedia
The microwave auditory effect, also known as the microwave hearing effect or the Frey effect, consists of audible clicks induced by pulsed/modulated microwave frequencies. The clicks are generated directly inside the human head without the need of any receiving electronic device. The effect was first reported by persons working in the vicinity of radar transponders during World War II. These induced sounds are not audible to other people nearby. The microwave auditory effect was later discovered to be inducible with shorter-wavelength portions of the electromagnetic spectrum. During the Cold War era, the American neuroscientist Allan H. Frey studied this phenomenon and was the first to publish (Journal of Applied Physiology, Vol. 17, pages 689-692, 1962) information on the nature of the microwave auditory effect; this effect is therefore also known as the Frey effect.
Dr. Don R. Justesen also published Microwave and Behavior at The American Psychologist (Volume 30, March 1975, Number 3)
Research by NASA in the 1970s showed that this effect occurs as a result of thermal expansion of parts of the human ear around the cochlea, even at low power density. Later, signal modulation was found to produce sounds or words that appeared to originate intracranially. It was studied for its possible use in communications but has not been developed due to the possible hazardous biological effects of microwave radiation. Similar research conducted in the USSR studied its use in non-lethal weaponry.
........................................