Audubon Minnesota organizes an annual “chimney swift sit” event, enlisting volunteers to stake out swift roosting areas — primarily smokestacks, towers and chimneys — and count the birds that roost. The first phase was in late July, and the second phase begins at 8 p.m. Friday and goes until 9:30 p.m. Sunday.

Chimney swifts generally roost about 20 minutes before sunset, according to Audubon Minnesota. Volunteers count and estimate the number they see going in to roost, record the time and location, and input their data on an online reporting form. Past recorded chimney swift data was used to designate two Minnesota areas (Upper Minnesota River Valley, St. Croix bluffs) as global “Important Bird Areas.”

Go online to mn.audubon.org and click on events to learn how to participate, get locations in the Twin Cities area and see results from past years. More than 9,800 swifts were observed in 2014, mainly at schools.