@Sheril Very interesting. I suspect the causes may differ by country - even so, I'm surprised changes in agriculture is not in the list here for the US as, here in the UK, it's by far the biggest reason. Perhaps, it's due to the sheer size of the US (unless they made a mistake).
Here, we got rid of hedgerows and killed all the insects off so there's no food other than in the towns and cities. I think it also explains why so many big birds like crows, magpies and pigeons have come into the city