I like the high pressure sprinkler answer, I nearly wet myself with the images of a soggy feline flipping through the air.

I don't know that I'd blame cats for a lack of birds in your area though. There seem to tons of cats up my street and no shortage of birds ( it's bloody loud round here at dawn! ).

The recent study into the London sparrow have shown that pollution killing off the myriad bugs sparrows feed on and people cutting down privet hedges etc. and replacing them with fences ( removing the cover that sparrows nest / hide in ) have done far more to curtail the sparrow population than any moggy. Carion birds ( crows and magpies especially ) will also tend to drive off smaller birds by mobbing them and knicking their eggs etc.

My cats seem far more interested in frogs and moths, so much so, they keep bringing them in to show me! Yech!

The mighty hunter
Returns with gifts of plump birds --
Your foot just squashed one

( From Morty's list of cat haiku she sent me, from whence she got them I don't know )

TTFN M'Lady P.