Roosting at mid-day. Several different groups, each with 10-25 butterflies in each group.
[Additional information contributed by observer, added by Journey North, 09/18/21]:
I saw the roost about 12:30 p.m. on 9/16/21. There were 3 roosts with 25-30 butterflies each and a couple of smaller groups with 5-10 each. I went back about 6:30 p.m. and there were only 30 or so butterflies left. Early the next morning (7:30 am) there were 25-30 butterflies.
This event was in a city park. There is a flower bed in the park with petunias and a few other annuals blooming. A few of the houses bordering the park have flower beds, but other than that, so significant nectar sources.
The overnight low was 60 degrees, The high that day was 87. The wind direction varied from 3 to 14 mph. There was a fairly strong wind from the south that afternoon, so I assume they were just sheltering for a while and then most moved on when the wind died down.
Most of them were in a large maple, but there were also a few in a white pine. The ones in the pine were very sheltered, but most of the ones in the maple were disturbed when the wind gusted.
I counted the number of butterflies in the largest group (30) and the smallest group (5) and then guessed at the total based on how the other groups compared in size.
Latitude: 41.4 Longitude: -92.9
Observed by: Wendy
The observer's e-mail address will not be disclosed.
Contact will be made through a web-based form.