Chimney Swifts, along with other aerial insectivores that eat insects while in flight, are of high interest in Wisconsin as they are a declining species. Swifts spend nearly their entire lives on the wing, only roosting at night or nesting inside chimneys, other structures such as silos, or rarely in trees, making it very difficult to confirm breeding. Here, with some help from Wisconsin’s Chimney Swift Working Group, we offer some tips for finding and confirming this unique species in your Atlas block.
Region: Entire state. eBird Range Map
Time of Year: Chimney Swifts arrive in Wisconsin in mid to late-April, with the majority arriving in May. They may be coded with breeding behaviors starting in the second week of May, if clearly not migrating. June and July are peak months of breeding activity. Some confirmations can still be made in August or even early September, but beware after early August because Chimney Swifts also use chimneys for roosting as numbers build for fall migration (sometimes in large numbers).
Breeding Guideline Bar Chart: (Full chart is on atlas handbook webpage)
Time of Day: Swifts start flying post-dawn and go to roost at or near dusk. While often found during those crepuscular periods, they could be nest-building or feeding young during any daylight hours from June into early August.
Focal Habitat: The best areas are small towns to large cities with adequate (un-capped and unlined) chimneys, although rural areas with appropriate silos or older farmhouses with good chimneys should not be overlooked. In the north woods, they may be found many miles from human inhabitation, where they nest in large snags in older forests.
Special Methods: Keep a close eye on fast-flying swifts in late May and early June as this is when you may see them flying low through the tops of trees that have thin twigs. Watch closely to see if these swifts “stall out” in order to snap twigs off for their nests (CN). Once the young hatch after an incubation period of 16-21 days (average 19 d), the parents will enter the chimney several times per hour. Be patient and watch closely, as swifts may slip in and out very fast and low and can easily be missed. Since swifts rarely enter chimneys except to roost at night or when the weather’s inclement, any swifts entering chimneys repeatedly (~several times per hour) confirms breeding (ON). The third way to confirm breeding is to listen, usually from inside the house, for high-pitched chatter from the young when a parent brings in food (NY). The nestling period is from 14-19 days; young birds emerge from the chimney for the first time 28-30 days after hatching.
Code Guidance: Use C for swifts performing aerial courtship displays. This V-display of pairs involves long glides with wings raised in a V-pattern and some rocking from side to side, usually within two weeks of arriving back on their breeding grounds. Use CN for carrying nesting material, or ON for likely occupied nests (swifts entering chimneys several times per hour, presumably feeding young), and NY if you can hear the young through the chimney. Be cautious about using N for visiting probable nest site. Only use N if you observe multiple entries and exits by 1-2 swifts during one observation period after June 1. Nonbreeding swifts also use chimneys, and some nesting pairs will tolerate nonbreeding birds using “their” chimney. In rare cases, you may be able to view the nest with eggs or young.
Other Species: Dawn and dusk surveys can be productive for detecting Common Nighthawks, which can sometimes be found in the same urban areas as swifts. Nighthawks are also declining aerial insectivores of high conservation concern.
Confusing Species: Few species can be confused with swifts. Swallows are similar in shape, but have broader wings, a clearly-obvious tail, never enter chimneys, and tend to be less crepuscular in activity.
More information about Chimney Swifts:
*Thanks to Bill Mueller, Karen Etter Hale, and Scott Diehl for being primary authors of this article.