Rod,
I am probably wrong but one very important habitat could be their overwintering refuge in Mexico. Global warming could effect overwintering survival there. One line thought is that they may age faster in a milder climate over the winter with fewer surviving to reproduce the subsequent spring.
In northern OK, one of the factors greatly affecting prairie spaces is the proliferation of blackjack oaks. In the past, trees were primarily concentrated along creeks. Fire suppression has allowed the blackjacks to take over. Even so, there is a lot of milk weed still around and again I don't think this loss of habitat is solely responsible. Even so, tens of thousands of acres of prime upland milkweed habitat have been lost there do to this influence. But probably most of that habitat was lost before 1980. Nowadays ranchers burn annually to keep trees at bay. Few are using herbicides there except for maybe hay meadows. Milkweed is especially abundant on heavily grazed land.
Last edited by jpsdad; 01/22/21 02:18 PM.
