Date: 09/17/2025

Number: 65

41.37435 N, -88.12267 W

1902 Hours

Approximately 65 monarchs in a common hackberry (Celtis occidentalis). One cluster on southwest side of tree, 6 meters above a trail. Second cluster had about 10 monarchs on the west side of tree above prairie restoration. Another 10 monarchs were roosting along in different areas throughout the tree and above 10 meters. Other monarchs would fly to explore tree then depart. It is possible that there were more, but with the leaves changing color and the dim lighting after sunset, it was difficult to determine. This was the largest roost located on September 17, 2025. Location is very close to the tree with the smaller roost located 5- 10 minutes prior.

Located right after sunset. 76 degrees (24.44 C). Sun has set on horizon at 1857 hours. Lighting is very dim. Light winds at 3 mph increasing to 5 mph from the northeast. RH 61%, Dew Point 62.

On Henslow Trail near at Midewin National Tallgrass Prairie (U.S. Forest Service).

Wilmington, IL

Latitude: 41.4 Longitude: -88.1

Observed by: Mike
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