Picnic area at Goose Lake Prairie has a copse of about 15 trees in the center and many more trees surrounding the area. Many of the trees hosted several roosts each.
[Additional information contributed by observer, added by Journey North, 09/10/21]:
We have spotted roosts in this area at Goose Lake Prairie the past 3 years and where we look for roosts (and have found some) at the local forest preserves in Will County, we always plan trips to Goose Lake when we start seeing reports at Journey North. It is a perfect setting for large quantities of monarchs. Goose Lake is the largest intact remnant of Illinois prairie left in the State. Nearby is also Midewin National Tallgrass Prairie.
We arrived at 6:00 PM and just started watching the prairie fields around the copse of trees. When we arrived, the monarchs were mostly nectaring out in the prairie. Around 6:30 PM, the sky above the copse of trees started to fill with monarchs coming in. There were 5 of us (4 Master Naturalists) in the group and as the trees started to accumulate clusters of monarchs, we spread out and started to look at how many clusters we were seeing and the average size of the clusters. Shortly before 7:30, the sky started to empty of monarchs "on the wing" and they were now settled in the trees. We compared notes and came up with the approximate 2,000 number. The number is probably on the conservative side because there were more trees on the perimeter that we saw monarchs "checking out" but did not go there to count. So, in other words, the monarchs were arriving that evening and I don't believe that had been there all day. Goose Lake Prairie is not close to where we live, so it is not something that we check out every day.
The trees that they were roosting in were mainly oaks, but there were also a few other species of trees in the copse that they were roosting in. I remember one was a black walnut and I really didn't take note of all of the other species of trees, but the trees are mostly white oaks.
There was little wind last night, but the way this picnic grove is set up, there are trees circling the parking lot on 3 sides with the the north side looking out into the prairie. At this time, Goose Lake Prairie had a lot blooming. There was, of course, a lot of goldenrod and many of the fall yellow blooming species like yellow ironweed, coreopsis, tall sunflower, the silphiums and boneset. I really wasn't focusing on all that was blooming.
On a side note, after going to this same location for several years now, and speaking to one of the people from the Illinois Department of Natural Resources that is based there at Goose Lake, this location is a definite "hot spot". The employee stated that even though Goose Lake Prairie is over 2,000 acres, the picnic parking lot is generally the only place that roosts form regularly.
Latitude: 41.4 Longitude: -88.3
Observed by: Phyllis
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