I write from Johnson County, Iowa.
What is the latest time in the breeding season that a pair of kestrels might take occupation of a nest box?
We have mounted boxes in a few new locations and do not have occupancy, now (almost May).
Should we consider blocking the nest box entrances until wintertime, or even until February?
Hi, Could we ask when the nest boxes were installed ( year and date) ?
If the nest boxes were install very recently it may take a while for the Kestrels to find them.
What type of landscape are they installed near or on ? Have you seen Kestrels in the area ?
Link to Kestrel Korner for info of our research, http://www.nu-sun.com/html/kestrel_korner.html
Have a nice day,
Nu-Sun Cinema American Kestrel Research Center
Winnipeg, Manitoba, Canada.
Thanks for reaching out! Kestrels have been documented initiating nests as late as mid-July in the Northern Hemisphere, with later attempts likely representing second nests within the season. So unless you're having massive issues with starlings taking over the boxes, we'd recommend leaving them unblocked and continuing to monitor them at least until then, as there's a chance that if one of your occupied nests fails a pair could try again in one of the new ones.
With the boxes being new, the lack of occupancy isn't unexpected (like Nu-Sun said, it often takes a year or two before kestrels move into new boxes). But all the same, observation data from empty boxes are still valuable for analyzing nest selection preferences and more.