Natural Notes: Take a swift night out!

The next time you are down on the ground pulling weeds out of our garden plot, look up!  On a hazy late afternoon you might see dozens of sooty-colored birds twirling around and around in the open sky.  And you'll hear a lot of "chatter chatter" calls as these graceful urban birds catch and gobble down insects.  These birds that you are seeing and hearing are most likely one of the few native city birds we have in Chicago, known as the Chimney Swift (Chaetura pelagica). 

You can view a short video clip of Chimney Swifts flying over the Chicago Lakefront:

Chimney swifts live up to their name, as their primary choice of nesting locations are in old, brick chimneys commonly found in older neighborhoods like the University Village neighborhood in Chicago.  Historically these birds likely nested in large tree snags, but as cities in the United States grew, the population of Chimney Swifts increased in correspondence with the construction of open brick chimneys. 

Chimney Swifts are fidgety birds that are always on the move.  You can recognize them by their silhouette, which resembles a "flying cigar" (see figure 1).  They are most active in the late afternoon until just before sunset, and at this time of year are often seen gathering in large flocks as they begin their migration southward. 

Figure 1:  Chimney Swift silhouette.  

Arriving in the spring to northern regions of the United States from far away places such as Central and South America, Chimney Swifts have adapted well to urban environments, feeding on many insects.  Brick chimneys, which are not often used during the warm summer months, offer nesting habitat where these crafty birds construct a tight-knit nest made of sticks adhered to a concrete or brick chimney with their sticky saliva.  Chimney Swifts have about one or two broods per year, and in less than two months the eggs will hatch and the chicks will reach adulthood.  Eggs are small and solid-white and are laid in a nest with a half-saucer shape.  At adulthood their feathers have a sooty brown-gray color, and they fly rapidly in circles as they catch and eat insects. 

Chimney Swifts can sometimes be confused with bats, but are easily distinguishable in a few different ways.  Chimney Swifts are most active during the late afternoon to just before sunset.  They are fast and graceful fliers who are also very talkative with their chattery call.  If viewed up close or with a pair of binoculars, gray feathers are a quick giveaway that these animals are birds and not mammals like bats.   

Bats are typically most active just after sunset and into the nighttime hours.  Bats in our region generally do not congregate in large flocks, and their flight pattern is more "fluttery".  Bat silhouettes lack the cigar-like shape, as well.  If seen up close, bats lack feathers and superficially resemble "mice with wings." 

Take a look at this video clip of Chimney Swifts catching insects just before dusk at the Taylor Street Farms in Chicago:

In recent years, Chimney Swift populations have been in decline.  One possible reason is that newer buildings are constructed with closed chimneys or no chimneys at all.  Capping of unused chimneys, or cleaning of chimneys during the nesting season, might also be contributing to their decline. 

By maintaining open chimneys, as well as constructing artificial nesting structures, Chiney Swifts can potentially be conserved.  But why would you want to purposely have an animal living (and defecating) in our chimney?  The answer is hopefully simple and convincing enough:  Chimney Swifts eat insects, including pest insects such as mosquitoes, and as such they play an important role in our urban ecosystem.  So the next time you decide to clean out your chimney, consider waiting until the autumn or winter, and leave your chimney uncapped during the spring and summer to allow our feathered friends a chance to raise a family. 

More information:  https://www.allaboutbirds.org/guide/Chimney_Swift/overview