Just came across this Chimney Swift study "Swift Watch - Summery Report" published in 2012. It has some great findings about the preference of Chimney Swift habitat and the availability in Ontario urban cities.
"These descriptions revealed that Chimney Swifts preferentially used chimneys with a greater length exposed above the roofline of the building and a greater inside area than those available to be used. The average chimney used by swifts extended 2.86 m above the roofline and had an internal area of 1.0079 m2.
We also found that 73% of active chimneys were found on non-residential buildings. Interestingly, the majority of building types surveyed by volunteers were residential houses (63%), followed by commercial buildings. However, the building types with the highest number of sites occupied by swifts were commercial (mostly found in downtown urban habitat), churches and schools.
... We found that among 139 open and suitable habitat chimneys available, only 24.4% were actually occupied by swifts. These results suggest that in urban areas there is more nesting habitat available than being used by Chimney Swifts and it is likely that declines in Ontario’s swift population are primarily driven by a process other than habitat loss, such as prey abundance and availability."
They also did a study on natural nesting sites in both logged and unlogged areas in Ontario. It would be great to know more about the study area (is it in Southern Ontario or Northern Ontario?) and whether there are preferred spots and distances away from cities where Chimney Swifts choose these sites. I've never read about chimney swifts nesting in anything other than chimneys!
Here's a bit on that study:
"Deciduous trees hosted 24 used sites, whereas 17 used sites were in coniferous trees. The most commonly encountered tree species to host nesting or roosting Chimney Swift were: white pine, sycamore, yellow birch, and cypress. In three reports, the entrance used by the Chimney Swifts was an entrance previously created by Pileated Woodpeckers."You can read the full report here: http://www.birdscanada.org/download/CHSWONReport.pdf
And this newspaper article reports on Chimney Swifts nesting in hay barns out on the East Coast:
"NOVA SCOTIA NATURALLY: The world of spectacular swifts"
written by Donna Crossland published on July 19, 2015 in the Chronicle Herald.
Other Posts on Chimney Swifts:
All about Chimney Swift Towers and the Birds (2011)
Chimney Swift Tower in Toronto (2011)