Date: 08/24/2010

Number: 275

September 1
We have had perhaps a hundred or more Monarchs on the back hills for the last few days. They have been feeding almost exclusively on goldenrod. Tonight was the best chance for them to roost, and I did spot two small gatherings of three or four butterflies---hardly qualifying for clusters, but the best I've ever seen back there. I make the entry to establish this information: the temperature was falling from 70 towards 60, but only reached 64 by dark. I think that fact was crucial in the lack of a good roost. The wind was calm, and the wind had been mostly south for the past week, allowing the butterflies to accumulate and feed extensively. A factor working against roosting on our back hills are the absence of dominant trees......the entire pasture area of some 60+ unfarmed acreage is surrounded and partly overgrown with smaller trees. The presence of so much wooded area around their feeding area tends to encourage the butterflies to enter the woods in many varied places. But I'll keep trying.

August 24
Had a successful search for roosting Monarchs tonight (August 24th). The wind was westerly today and so most of our Monarchs held. Temperatures were falling from 70 degrees at about 6:00 to 60 degrees when I got home at 8:00 or 8:30. We ended up getting morning temperatures in the low 50s (about 53 for a low at home, and 55 at 7:30 a.m.) Monarch clustering is a very good indication of temps falling below 60 degrees. (Tom Murphy told me last year that he thinks 57 or 55 is the magic number for monarch clustering behavior.)

The Monarchs at the alfalfa field I found yesterday (August 23rd) were done feeding by 6:30. I saw only three butterflies when I walked across the partially cut alfalfa. In fact, I thought maybe the whole bunch had migrated. Then I started to see scattered Monarchs along the wood edge that borders the field, but only ones and twos.....nothing resembling a roost except for three or four that fluttered around one tree. I walked to the corner of the field, where it was much lower ground, and there I found a small cluster of maybe five, but they spooked--at least that's what I thought.

I continued walking the edge of the field, videotaping singles and doubles along the tree edge, mostly silhouette shots as they searched for roosting spots. I found one more small bunch fluttering around the east end, but the sun was setting and so I decided to retrace my steps and check the two earlier possible roost sites.

It was lucky I did. The corner low spot was now a good roost and getting better with each minute. I taped it for about 15 minutes and when I was just about to leave the group became very agitated and there was a swarming effect as they left their roosts and returned again and again. It was quite amazing. Much like watching a swarm of bees. The roost was the largest I have seen.......I'm guessing there were six dozen or so, maybe more. Before it got completely dark, I hiked back to the earliest spot I had hopes for, out near the road. I had about given up on finding anything when I saw a fluttering in the last main tree on the fencerow. There turned out to be three clusters there......I'm guessing 50-75 butterflies > between them all. Counting all the
butterflies I saw walking the field edges, I'm guessing there must have been 200 or more on Bill Thiel's alfalfa field. (Thanks for sharing, Bill!) To cap the evening off, a full moon was rising as I walked back to the car.
What a night.

Osceola, WI

Latitude: 45.3 Longitude: -92.7

Observed by: Pat
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