When something novel grabs our attention, our perceptual systems become more sensitive to it, and we become more likely to perceive it again. This perceptual phenomenon also happens with media attention, and can — and does — create the false appearance of epidemics or other connected events.
In this case, it’s clear that these bird-death events happen fairly often — the media just didn’t “discover” them until a relatively large event occurred. Now the less scrupulous news outlets are hyping new bird-fall events as if some new and mysterious force is behind them all.
This reminds me of mass-hysteria or false-syndrome cases, in which one apparent case of something new draws attention, triggering the “discovery” of further “cases” in a population where the same symptoms are already relatively common.