Monarch roosts continue to progress south as the monarch migration picks up, with reports moving into Illinois, Iowa, and Indiana.
If you look at the Journey North roost maps, the southern half of Minnesota and northern half of Iowa have the highest concentration of monarch roosts this year, with quite a few reports from southern Ontario as well.
We first started receiving reports from Minnesota in mid-August, and reports continue several weeks later.
In Barnesville, Minnesota, Doug reported 18 roosting monarchs on Sept. 8, writing, “Saw 2 roosts this morning of six and 12 in bur oaks. A couple of the monarchs seemed especially large and a bit lighter in color than usual. Going on about 4 weeks here with roosts; hope this equates to a strong overwintering population.”
Doug's first roost report of the season was on Aug. 15, with an estimated 880 monarchs sighted.
We're still receiving some large reports from the North Star State. In the southeastern corner of the state, Bronwyn estimated seeing 2,000 monarchs on Sept. 8, writing, “We have acres of milkweed and native grasses and prairie flowers.”
In Faribault, Minnesota, not far south of the Twin Cities, Angie reported an estimated 1,000 monarchs in a roost on Sept. 7.
South of the Minnesota-Iowa border, in Buffalo Center, Don reported 500 monarchs on Sept. 7, writing, “Lots of trees have them roosting here. They are trying to stay out of the wind.”
Among other reports from the Hawkeye State, Erica in Fredericksburg reported 20 monarchs on the same night.
Despite having the most reports of any area, Minnesota and Iowa aren’t the only states where monarchs are congregating.
To the west, a volunteer in Aberdeen, South Dakota, reported seeing approximately 500 monarchs during a quick count on Sept. 6. We also received a roost report from North Dakota, with Angelique reporting 30 monarchs on Sept. 8.
In Arlington, Wisconsin, north of Madison, Emma reported an estimated 596 monarchs on Sept. 9, writing that most were roosting on the south-facing side of trees. A volunteer in Green Lake, Wisconsin, estimated seeing 1,000 monarchs on trees throughout a field of blooming buckwheat on Sept. 6.
Mike in Wilmington, Illinois, reported 375 monarchs along 2/5 of a mile of trail in Midewin National Tall Grass Prairie, with the largest being 55 monarchs in a hackberry tree.
Jessica in McLean, Illinois, reported 28 monarchs roosting on Sept. 3, and the southernmost roost in Illinois so far came from Trish in Ivesdale on Sept. 8, who reported 14 monarchs in a windbreak just southwest of Champaign.
On the eastern end of the Great Lakes region, Dianna reported 83 roosting monarchs in Richmond, Indiana, on Sept. 8. Reports continue from Ontario, as well.
“Monarchs have been there for a few days,” Karen in Sarnia, Ontario, wrote on Sept. 9 alongside a report of 1,000 monarchs. “Trees are right next to a clover field, so that might be what is attracting so many.”
On the northern shore of Lake Ontario, Sarah reported 500 in oak trees on Sept. 5, and Claudia reported 150 in maples on Sept. 7.
What are monarch roosts?
Monarch butterflies migrate alone during the day. They come down at night and gather in clusters, called roosts.
Some roosts have only a handful of butterflies, while others will have hundreds or even thousands. Some last for only a night or two, while some trees will be filled with monarchs for a week or longer, and some areas will be used year after year as monarchs make their annual southbound migration.
Having trees that provide some shelter from the wind as well as nearby nectar sources may be two important considerations as monarchs choose roost sites. One hypothesis for why monarchs roost is that it's an anti-predator strategy. Cool temperatures paralyze monarchs, making them vulnerable to predators, so a roost could provide some safety in numbers.
Report fall roosts
You can report fall roosts by visiting the Journey North reporting form. Select “Monarchs & Milkweeds” as the project, then “Monarch Butterfly” as the species. Then, you can select “Monarch Fall Roost” as your life stage or type of observation.
It’s important to note that not all monarchs landing in trees constitute a fall roost. Monarchs may land periodically in trees to rest or sun themselves to warm up.
If you see multiple monarchs gathering in the evenings and settling in one place, you may be seeing a fall migratory roost, or you may see what’s left of a roost in the morning before monarchs take off again for the day.
Other activity
While we tend to focus on migration this time of year, there’s plenty of other monarch activity going on, including continued breeding. You can view all of the other Journey North maps here.
So far this week, at the same time we know monarchs are roosting near Champaign, Illinois, we received a report of monarch eggs courtesy of Russ in Champaign. This is a good example to show that not all monarchs are migrating now. Monarchs that emerged earlier in the year may still be laying eggs, as they are not migratory monarchs that have delayed reproductive diapause to take on the fall migration.
Other recent egg reports come from South Carolina, Pennsylvania, North Carolina, Georgia, Missouri, Delaware, Massachusetts, Tennessee, New York, and more.
From roost reports of 1,000 monarchs to reports of a single monarch egg, larvae, or adult, we appreciate all of your contributions to Journey North!