Question

If it is an advantage to be a food specialist and thereby avoid the extra competition that generalists face from other generalists, then why aren't all birds specialists?

Answer 1

All birds should not be specialists because in this era of increasing urban sprawl and habitat fragmentation, birds with fewer specific environmental requirements are far more successful than birds with many. This is because ecosystems are being chopped up, parceled out, and paved over everywhere hence specialist species are more likely to suffer from habitat loss and disruption than generalist species.