There’s no doubt that animals are highly adaptable to their surroundings. And a perfect example of this is a group of chimney swifts that has recently taken up temporary residence in the Mokena Village Hall on Carpenter Street, gathering in an old chimney as they prepare to migrate south for the winter.
The village building is in the older section of Mokena, and the chimney swifts have been congregating there in the fall for at least the past several years, said Jessica Prince-Sharrar, education and outreach supervisor for the Forest Preserve District, who happens to live in the neighborhood.
Prince-Sharrar and some other neighborhood residents enjoy the annual visit from the chimney swifts, spending time outdoors watching the birds in flight.
“We go out there and watch them every night,” she said. “It’s like a little social hour.”
As their name implies, chimney swifts often nest in chimneys and similar structures. At this time of year, the birds congregate in preparation for migration, and sometimes hundreds or even thousands of chimney swifts may be roosting in one large chimney.
Using chimneys for roosting is an adaptation for the birds, which used to use hollowed out tree trunks as roosting spots. When much of the land in the U.S. was cleared for agricultural use, far fewer nesting spots were available, so they also began roosting in chimneys. While chimneys and similar structures – air vents, silos, barns and old cisterns – are the most common roosting spots, they do still sometimes congregate in hollowed tree trunks.
The flock of chimney swifts in the Mokena village building could include as many as 1,000 birds, Prince-Sharrar said. That number increases, too, as the days go by, with more birds joining the group as they prepare to travel south for the winter.
Prince-Sharrar said having the chimney swifts in her own neighborhood is “kind of a treat” because although chimney swifts are not an endangered or threatened species, their population is declining. They are considered a Common Bird in Steep Decline, according to the 2014 State of the Birds Report.
Among the reasons for the decline is a loss of habitat, Prince-Sharrar said. They are also affected by the use of herbicides and pesticides. As insect eaters, these attempts to control bug populations can be detrimental to their diet and ultimately to their health.
Chimney swifts eat all manner of bugs – beetles, ants, flies, bees, wasps, etc. – and they catch them in flight, the Cornell Lab of Ornithology reports. In fact, the birds spend their entire lives in flight except when they are roosting or on their nests. They mostly forage over open lands but, as the flock in Mokena would indicate, they can also be seen flying over residential and urban neighborhoods.
According to the Cornell Lab of Ornithology, their fall migration takes them from the eastern United States and Canada all the way to South America. Their stopover in Mokena will be temporary, with the flock departing the area during October, Prince-Sharrar said.
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