Darwin talked about bird deaths around him during the winter. By his estimation, he thought ~3/4 birds would die of starvation every year. A massive amount. He

Darwin talked about bird deaths around him during the winter. By his estimation, he thought ~3/4 birds would die of starvation every year. A massive amount. He commented that a plague of 1/10 people would be a near apocalypse, yet many fauna experience this year after year. So, with a fecundity like that, it is a big deal that ~1/3 birds aren't returning relative to baseline. Something big really is happening to do devastation like that. I don't know the modeling and the second order partial differential equations to really say something (read the article, obviously), but I can say that reductions like this are big deals.