Many people are puzzled or excited when bluebirds (which may have disappeared in the summer after nesting season ended) show up again in September and October and visit nestboxes. The birds usually do not bring any nesting material to the box, although the female may spend some time inside. They may chase off intruders, and males may perch on the roof, wingsave and sing like they do in the spring. You may also see flocks of bluebirds.
More than 160 years ago, Henry David Thoreau witnessed the same behavior, and wrote about it in his journal on September 29, 1842
"Today...the bluebirds, old and young, have revisited their box, as if they would fain repeat the summer without intervention of winter, if Nature would let them. "
"The first southbound migrants were noted during the first half of September, and until the end of the month a rather gradual, daily increase in numbers was observed. The migration reached its peak in October, when the bird was as numerous as in spring. In autumn its lisping note, uttered from overhead or from a fence post or tree, was one of the most pleasing and familiar of all fall bird calls. The Eastern Bluebird was very conspicuous during the calm, warm 'Indian summer' days of late October--such weather was called 'bluebird weather' by local sportsmen."
What are they up to? Are they confused? Homeless? Thinking about starting another brood so late in the year? Unlikely. I think the reasons bluebirds (and other species like chickadees) check out boxes in the fall may be any or all of the following:
Prospecting: previous residents scope out future nest sites or migrants passing the area get curious. (Eastern Bluebirds may leave for migration from early September though December, depending on the location (BNA).
Practice (e.g., young birds)
Weather (temperatures and day length) mimic breeding season temperatures so it is possible they are confused
Looking at spots for roosting. Note House Sparrows WILL use boxes for roosting. Do not allow this, as it gives them a jumpstart on the next nesting season. Consider inbox trapping (http://www.sialis.org/hosp.htm#nestboxtraps.))
That is why it's a good idea to put up any new boxes in the summer or fall. It gives birds a chance to check them out BEFORE they migrate. Maybe they will be back to nest in that box the following year. It also lets the boxes weather a bit. Some folks think birds prefer a weathered box (although I haven't seen any definitive research conclusions on that issue.)
See high quality, interesting video of bluebirds hanging around a nestbox, hacking up hackberry seeds, iwishicouldfly.com
Suggested Fall and Winter Bluebirding Activities:
Clean out boxes: I try to do this after each nesting, but better late than never. More....
Roosting: Prepare nestboxes for winter roosting by sealing up ventilation holes (with removable Mortite rope caulk, styrofoam, cardboard, or a strip of wood), and/or insulating the floor. More information.
Downy woodpeckers seldom if ever nest in boxes, but they will roost in unused boxes, usually arriving right before dusk. Sometimes they excavate the interior a bit.
Waterproofing: Late summer (after nesting season ends) or fall is a good time to do annual waterproofing of nestboxes, because you should do it when the box is not in use. Double check the caulking of the various seams of the box and re-caulk if needed before waterproofing.
Icicle Prevention: If you're in a really cold climate, and the roof allows icicles to form in front of the entrance hole, birds could get trapped inside. To avoid this:
mount the box so the box is tilted slightly to the side so water drains away from the entrance hole, or
make boxes with a roof that is slanted so it drains to the side or the back, or
Add a longer roof to extends farther away from the entrance hole.
Repairs: If you opt to leave your boxes up year-round, take measurements of the various parts of your nestbox to have them handy for winter days of making repair parts. Sometimes wintering critters will chew or excavate your boxes resulting in springtime repairs being needed. By January (southern blues are real close to nesting), you should have ready various repair parts for your boxes - new interior wall liners might be needed if woodpeckers roosted. Replacement hole-guards might be needed. New box-fronts or hole repair pieces to 'fix' an entrance hole that may have been enlarged by squirrels, woodpeckers, mice, etc. By mid-winter, begin checking the fasteners that mount your boxes on their poles, to be sure none have broken, rusted, or worked loose. This can save a fallen box during nesting season.
Take down or leave up various shade devices, unless you want to use them to shield against raging winter winds.
Keep an eye out over the fall for when field grasses start dying - time to collect lots of soft dead grass for IN CASE replacement nests are needed next year. See how to do a nest change.
All winter, take your preferred steps concerning House Sparrows if they are in your area.
Feed: Offer suet (you'll have to train them first) when temperatures are below 40 degrees and insects are not active.
Water: Eating snow for moisture uses up extra energy. A heated birdbath can help birds, but your electric bill will go up. You can also use a heated dog food bowl (less expensive than a heated birdbath) with pebbles in the bottom to keep it shallow.
Here's another little poem excerpt, written by Susan Stiles in 1973
When the frost is on the punkin' and when leaf and branch diverge,
Birds with hormones reawakened sing a paean, not a dirge.
What's the reason for their warbling? Why on earth this late-year splurge?
The autumnal recrudescence of the amatory urge.
"in October, transient Bluebirds are abundant, and natives come back as if to say good-bye to their homes, and sometimes carry nesting material into their boxes, in that Indian summer of the procreative instincts that many birds evince on warm October days."
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