Interestingly not mentioned is that many migratory birds that go through Europe pass through a lot of hostile territory. Covered several years ago by none other than Jonathan Franzen:
Maybe not a significant reason for the decline; I don't know, but obviously you can't blame the conditions in France alone for a decline in 70% of migratory songbirds. France could not be the issue at all.
EDIT: it’s fascinating that HN has people that don’t get that disbalancing a fairly balanced system (ecosystem) will lead to severe and, usually, hard to predict results. Birds and insects make up a vital part of our shared ecosystem. By breaking the balance in it further and further we are indangering ourself a further and further. The equation will balance itself, but that balance may or may not include us (humans) in the long run. I’d prefer we make significant concessions now, rather facing such dire consequences later.
http://ngm.nationalgeographic.com/2013/07/songbird-migration...
Maybe not a significant reason for the decline; I don't know, but obviously you can't blame the conditions in France alone for a decline in 70% of migratory songbirds. France could not be the issue at all.