Reportedly, 2019 is a "Mast" year. A mast year is one in which trees and other plants produce exceptionally high amounts of seed. In fact, this time its said to be the biggest seed-spreading "megamast" in nearly half a century. This means more food is available for predators like rats, stoats, possums, mice and more, and consequently they will breed more and cause more havoc killing our native birds and eating their eggs.
So what has this to do with Monarchs? To begin with the warm temperatures mean that the butterflies are still flying and, even more unusual, the butterflies are apparently still mating, eggs are still being laid and caterpillars are still emerging and growing.
On a negative side, the mast year means that Monarch predators are doing better than usual, for the time of year. Asian Paper Wasps were still around, well into Winter, but we are not seeing any right now. German Wasps are still very much around, now, in large numbers.
If you look at the milkweed that the caterpillar is on, in my photo (above), you can see the leaves are infested with Aphids. Aphids were showing strongly on all the plants the caterpillars were eating, in the area I photographed them.
I, for one, will be interested to see what happens when Summer comes around again.