can anyone verify the following?

i once heard a theory posed about the extinction of Passenger pigeons (besides their wanton slaughter and habitat destruction). the theory goes something like this:

after many of the birds had been killed their population reached and dropped below a lower threshold at which the birds could not get 'excited' enough for the hormone spike needed for the birds to reproduce. in other words, the flocks had to be a certain minimum size in order for them to produce the necessary sex hormones for mating and reproduction. this is thought by some to have been the nail in their coffin after all the slaughtering, becuase even though there were a handful left (say 10000), this was enough of a bottle neck for reproductive success reasons for all of them to perish for good.

if anyone can verify this theory with links, author names, book titles where i could find documentation i would reaaaaallllly appreciate it.

thanks in advance.