I think the birds are heading in-land for no fault of their own, just the fact that, there are no longer huge sandeels shoals all along the coast which helps sustain everything that feeds on them. Instead they are ground up and used as farm feed and fertilizer etc!
I remember I guy I used to work with telling me, when he was a lad,, he could take a net down to hamworthy beach and in a matter of seconds fill it with eels.