Monarch Butterfly Population Crash

Monarch Butterfly populations are dropping rapidly. This one was in my garden just now.

This was a second Monarch, near the first, nectaring on Verbena bonariensis. You can see this one has worn or damaged wing tips.

Just photographed these Monarch Butterflies in my garden. They have become rare as hen's teeth here in NH with reports of population crashes in many other places in the country as well. There were two in the garden just now and they were nectaring on Verbena bonariensis, which I plant a lot of just for the butterflies.
Some think the population drop is due to a loss of milkweed, their larval host plant. That is the only plant on which they lay their eggs and their caterpillars eat the milkweed then pupate and turn into the adult butterfly. Milkweed has gotten wiped out in the midwest due to pesticides as well as drought last summer. Monarchs go to Mexico to overwinter in a few mountain pine forests and those places are also under threat from logging.
So sad to think their populations are plummeting, not sure what the future holds for them. But also so special to have two in my garden today. Safe journey.