Yesterday afternoon, my mother reported that my uncle had told her that the monarchs were numerous in a little park across the street from our shore houses. A good flight was passing through Cape May Point the same day, so on my way home from there I decided to stop in at Stone Harbor Point as evening approached. SHPt has built up some wonderful natural habitat in the 18 years I've lived here full time, and has become a reliable spot for spotting migrating fall monarchs.
We'd had couple of well-populated roosting sites (~1500-2000 individuals Saturday, ~1000) Sunday in just one location at the very tip of New Jersey over the weekend, so I figured I had a chance at finding a roost at the end of Seven Mile Island as well on Monday. Monarchs migrate during the day and settle together in evergreens to wait out cool fall nights; the island had a bunch still flying south as I drove through, so I knew they were going to have to put down somewhere well north of the jumping point for crossing the Delaware Bay some dozen miles to the south.
As I had noted the evening before farther south, quite a lot of monarchs were still fluttering indecisively about Stone Harbor Point. After a quick walk up to the dune crossover to see what was coming in from the north and where they were heading (and to note that the goldenrod a mere ten miles or so north of Cape May Point was about a day or two behind the full bloom that had just started in Cape May), then down the dirt road to check out the vegetation, I returned to the parking lot only to find a roost literally at the end of the street I'd come in on.
One windswept cedar was collecting the majority of the butterflies--as well as a Red-breasted Nuthatch who politely remained on the windward side of the tree and left the roosting (and toxic) monarchs alone. Interestingly, a few lone monarchs had taken up perches on a couple of other trees… The human theory on communal roosting is that it provides protection-in-numbers from predators that don't know not to eat the bright, don't-eat-me colored butterflies (toxic due to the fact that their caterpillar stage consumes only milkweed, can tolerate the poisonous stuff and then incorporate the toxins into the adult butterfly) and possible insulation from cool night air due to the sheer body mass that can accumulate in a big roost during a large wave of butterfly migration.
A roost of about 85 individuals doesn't pack nearly so much punch as seeing twenty times that amount, but it is still pretty damn impressive.
As you can see, monarchs roost with wings closed. Not only does this reduce surface area (thereby conserving as much heat as a cold "blooded" animal is capable of), the underwing pattern provides a relatively effective camouflage; I certainly had to look twice to tell monarchs from dead cedar twigs when not so far away… But incoming individuals tend to disturb the already-settled ones, rousing the roost into motion. I was certain I could hear wee little voices exclaiming "Eh, don't land on me!" and "Hey, I was here first--go find your own spot!" as new butterflies circled in to land and the dead-still ones fluttered briefly back to life with whisper-light complaints.
And not one of the half dozen or so people that drove into the parking lot while I was there asked me why I was staring into a seemingly empty, scraggly tree…