Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters




The last batch of bluebirds fledged from our small trail in northeastern CT on August 10, 2004. Generally I think trail results are like dreams – only interesting to the person who has them. But that won’t stop me from sharing some stats, and some lessons learned. (I also report data to the North American Bluebird Society [NABS], The Birdhouse Network [TBN-Cornell], CT Dept. of Env. Protection, and Massachusetts Bluebird Association.)

SUMMARY: Total number of fledglings (114); and number of bluebird pairs, clutches (3) and fledglings were double to triple what they were last year; probably because of weather (thank you global warming), more boxes (with empties available) in great locations, significant reduction in local House Sparrow population and competition (due to use of passive and aggressive control methods described on, and mealworm feeding. Bluebird nesting started two weeks earlier, and lasted a month longer. Bluebirds had three clutches for the first time. I believe two pairs of Tree Swallows had second broods (extremely rare per TBN). Many more House Wren dummy nests in different locations. Only two nestlings lost (Tree Swallows in late nesting – reason unknown). Peterson box utilization was 100%.

Sincere thanks to the Hansen, John, Hosmer and Chapuis families; and the Town of Woodstock for hosting nestboxes. And thanks to the generous people like Wendell and Cher who let me use their awesome photos (since birds in my photos resemble blurry ants), and those who patiently share their wisdom with me so I can improve the usefulness of the website, and improve my own bluebird conservation efforts.

LESSONS LEARNED (i.e., mostly things I did wrong. I’m still new to bluebirding. I imagine I’m not the first person to make these mistakes and could have learned from the experience of others….)

  • Even with a really patient and committed husband armed with a pickaxe, it is not possible to put up new boxes in February when the ground is frozen solid. Do it in October/November. That way, downy woodpeckers, nuthatches and others will have cozy places to roost, and they’ll be in place if blues show up early.
  • Don’t let House Wrens nest – if they start to add sticks, leave the box open for 1 to 2 weeks. Otherwise they may take over the trail, filling 1/3 or more boxes with dummy or active nests, making them unavailable to birds working on a 2nd or 3rd brood, and increasing the local wren population, which will probably result in even more nestings in subsequent years. I also noticed that their cheerful song can become grating after hearing it over and over and over and over and over.
  • Don’t try to open a Gilbertson box with one hand. I had a camera in one hand, and was taking the box off with the other, when a chickadee flew out in my face (even though I had tapped on the box), startling me. I dropped the box and EVERY SINGLE chickadee egg broke. Major guilt trip.
  • Chickadee eggs are very fragile (see above). While trying to get an egg count in a box that was mounted high, I lightly touched them and broke one egg.
  • If you use a battery driven screwdriver to mount sparrow spookers, remove the nest while mounting, as movement might addle eggs. I didn’t do this for 2 nestings, and one egg (don’t know if it was the one in the box when spooker was installed) failed to hatch in each clutch. All eggs in the third nesting (undisturbed by drilling) by this pair hatched.
  • Have empty boxes available for latecomers and second and third broods.
  • Soap interior (roof and walls) of boxes BEFORE nesting season in locations where paper wasps tend to show up. I almost had one box abandoned by bluebirds when a paper wasp started to build. Fortunately I caught it quickly in the midst of bluebird nest building and the blues returned to the box.
  • Keep better records and check all boxes regularly. I lost track of some activity when I traveled for work. I also didn’t get accurate counts of Tree Swallows because the female wouldn’t budge and I didn’t want to disturb her. I stopped checking some boxes after bluebirds fledged (because I’d never had a second brood) and was totally surprised to find a complete nest with eggs that may have been started before the previous brood fledged from another box. I was checking one box with Tree Swallow nestlings once a week and that may not have been enough – I found a nestling inside that had been dead for days, covered with maggots (quite disgusting.)
  • Leave Tree Swallow nests in place for 1-2 weeks before cleaning boxes, in case they might be reused for a second brood. I had two Peterson boxes in primo habitat reused almost immediately (building a new nest on top of the old one) by Tree Swallows that I think were the same birds who had earlier broods in these boxes, because there were other empty boxes in the area that new latecomers could have used. Unfortunately it’s not possible to be certain without banding.
  • House Wrens are prone to premature fledging if the box is opened late in nesting cycle
  • Forget trying to feed peanut butter suet in a mealworm feeder without a predator guard. Red and gray squirrels are relentless. Starlings love peanut butter suet, so use a cage inside a cage to feed.
  • Wren guards don’t appear to prevent wren entry once they’re active in a box. Wrens may rip out nests of other birds before building their own, and can be very aggressive about claiming a box even if they just end up putting a dummy nest in it.
  • When trapping House Sparrows in a nestbox, let them put a little nesting material in first, and try to trap both male and female by immediately resetting the trap. If the second bird is wary, try putting the first captured bird (and/or nest with eggs/nestlings) in a ground trap underneath the nestbox.
  • When ground trapping House Sparrows, put decoys in an adjacent birdcage with roof and easily removed water/food trays. Feed mealies to decoys to keep them healthy. As soon as you see parents bringing fledglings to food source, put out traps as you may catch the whole brood. (Thanks Keith Kridler!)
  • blow flies may not be able to chew through a coffee filter, BUT the flies lay their eggs on or under the nestlings, so putting one underneath a nest doesn’t help. You need to replace the nesting material first. (Thanks Terry Whitworth!)
  • Even though you trap every House Sparrow that shows up in your own yard, when you expand the trail to neighboring areas, you have to recruit neighbors to help control House Sparrows.
  • Don’t bother with winter trapping in CT – too many non target birds (juncos, chipping sparrows) are drawn to the trap, and it keeps getting buried in snow.
  • Bring captured House Sparrows/starlings to a local bird rehabber (mine even picks up!) They are volunteers that usually really need the food for their injured birds.
  • It’s actually possible to get a little tired of a bluebirds’ song. One male (abandoned after nestlings fledged) sang for more than one month solid on the telephone wire in front of my house. I think he finally hooked up with a female (the one who dumped him after the first nesting?) for the last brood of the season.
  • It’s possible to see a FLOCK of bluebirds! I’ve been swarmed by eight or more birds at the mealworm feeder. And to think I had never even seen a single bluebird prior to 1998.
  • New cedar boxes swell up when it’s humid and are almost impossible to open.
  • When puncturing (House Sparrow) eggs with a needle to prevent hatching, don’t use a really tiny one (like a #8 quilting needle) as the egg might still hatch.
  • Don’t buy dogwood berries in the spring and keep them in the refrigerator. They’ll rot, and the bluebirds aren’t interested in them when bugs are available.
  • Use predator guards on all boxes. I had a red squirrel chew up a box on fence that didn’t have a guard (because I was using it for HOSP trapping). If native birds had been in there, the squirrel could have raided the nest.
  • Dump mealworm shipments from box/muslin shipping bag in a white plastic garbage bag, then transfer into holding containers.
  • Pairing boxes AFTER bluebirds started nesting may freak them out or confuse them.
  • The Carrier slant box may be utilized by House Sparrows, and is not particularly attractive to other cavity-nesters.
  • Put metal hole guards up on all boxes to prevent chewing/predation (available from The Bird Watcher’s General Store.) They also look sporty. Keep various sizes on hand – as soon as chickadees pick a box, put one up to protect them from competition.
  • You can make a quickie mobile mealworm feeder (to help out parents who need to feed nestlings every 15 minutes) with a length of PVC pipe with two holes drilled in either side, PVC caps on top and bottom, a roof of plywood or plastic screwed on, and a cat food can on top (since the birds prefer to eat from the top). Hang it from a mobile shepherd’s crook.
  • Wrens will nest in the PMCA starling/House Sparrow nestbox trap (entering via the hole in the vent in the side even when the trap is closed).
  • The first boxes picked for nesting were Petersons. Starlings didn’t raid them, but I recognize this is a possibility in the future. In this area, starlings haven’t shown an inclination to use nestboxes (even the metal purple martin house I have up.)
  • If you get Peterson boxes from Ahlgrens, buy them assembled. It’s worth the extra 2 bucks.
  • Don’t assume others are familiar with the basics of bluebirding. One person who got a nestbox as a gift put the box out in the yard sitting on top of a tree stump. Provide informational handouts (e.g., to people who are interested in learning more.
  • Not everyone is as interested in bluebirds as I am, and most normal people usually slip into a coma after about 5 minutes of bluebird blather. (If you’ve read this far, you probably qualify as goopy over bluebirds – see



  • # boxes: 28 (compared to 13 in 2003)
  • # property owners hosting boxes: 7 (up from 4 last year)
  • Locations: 7 on lawn, 9 Christmas tree farm, 4 meadow, 2 closed landfill, 4 adjacent to woods. 15 of those with streams/wetlands/pond nearby.
  • Types of boxes: 1 Carrier Slant (experimental), 5 Peterson, 1 Gilbertson, 22 NABs (small and large). 1 Purple Martin Conservation Association starling/House Sparrow nestbox trap was used by House Wrens - that’s included in the 28.
  • Predator Guards: PVC pipe with cap, mounted on hose clamp so it wobbles
  • Paired boxes: 2. Neither were used (except for one failed House Sparrow attempt.) When given a choice between a Peterson and NABs box paired, the Tree Swallows picked the Peterson.

Mild, excellent weather all season long. No excessively cold & rainy periods (unlike 2003). Late in season, temperatures were rarely in 90’s.


  • First bluebird nest begun ~ 4/3, first egg 4/13 (compared to 4/21, with first egg 4/28 in 2003)
  • Last bird fledged 8/10 (compared to 7/12 or 7/13 in 2003, from a second nest attempt after first nestlings died, possibly from hypothermia)


  • # birds fledged: 114 (compared to 29 in 2003)
  • # successful bluebird nestings: 6 (compared to 1 in both 2002 and 2003)
    # bluebird nesting pairs: 3 (one “friendly” female may have been involved in 3 broods, mating with a different male on the second brood)
  • # bluebirds fledged: 26 (compared to 4 in 2003 and 5 in 2002), from 6 nestings.
  • # of bluebird pairs with second and third broods: 2 pair (compared to 0 in 2002 and 2003. Both those years I only had one pair with one brood.)
  • # Tree Swallows fledged: 67 (compared to 13 in 2003)
  • # chickadees fledged: 9 (compared to 2 in 2003)
  • # titmice fledged: 6 (compared to 5 in 2003). However titmice appeared to successfully nest in natural cavities, as many more fledglings were seen near feeders.
  • # House Wrens fledged: 6 (2 pairs. However, they tried to use 9 boxes, with 13 nests.)
  • # House Sparrows fledged: 0 (no House Sparrows are allowed to successfully nest on the trail.)
  • # failed nestings (nest construction began, no eggs/nesting interrupted. Does not include House Wren dummy nests or House Sparrow nesting attempts): 3-5.
  • Weirdness: two nests with no cup, never used for eggs. After third brood of bluebirds, one box filled with loose grass – no cup. Not sure what species did this.
  • House Sparrow nesting attempts/box claims: 10 attempts in 6 boxes.
  • # House Sparrows trapped/shot: ~39
  • Second bluebird nestings (assumed same pair, not possible to confirm without banding) occurred in different boxes than those used for the first nesting.


  • Predation: Six chickadee eggs disappeared, presumably from House Wrens who subsequently tore out chickadee nest and built a dummy nest. All boxes used by bluebirds were equipped with sparrow spookers ( after first egg was laid. Most had monofilament to deter House Sparrows. We do have plenty of starlings, and raccoons in the area, but not many snakes (thank goodness.) No known losses to mammalian/reptilian predators.
  • Dead/missing nestlings: 2 (Tree Swallows in late nesting. 1 missing, 1 dead in nest). Cause unknown. Other 2 nestlings were fine and fledged.
  • Broken chickadee eggs (accidentally by me): 7. (One nest abandoned as a result.)


  • Install 13 more boxes at the closed Woodstock landfill (adding to 2 existing), after checking with the State to ensure installation doesn’t impact cap, etc. Put up five each Gilwood (see plans at – supposedly preferred by blues, not preferred by House Sparrows), Peterson and NABS to test preferences.
  • Work with Terry Whitworth on blow fly control techniques (e.g., hardware cloth raising nest off floor.)
  • Try feeding dogwood berries (ordered from Dan Finch, in the fall and spring, along with suet (to date no bluebird takers, but other birds love homemade suet.)
  • Try Steve Gilbertson’s recommendation to sand metal mounting pole smooth with steel wool, then spray annually with furniture polish (in lieu of a PVC predator guard.)
  • Try some more paired boxes (before nesting season starts). Have a total of 50 boxes on the trail (all I think I can manage.)
  • Experiment with different hanging methods (I’ve been using U-bolts.)
  • Learn more. Read every book and journal, watch every video, and read postings from forums and listserv. Go to NABs convention in Asheville if I can talk my wonderful husband into it.

A man's interest in a single bluebird is worth more than a complete but dry list of the fauna and flora of a town.
- Letter, November 22, 1858, from Henry D. Thoreau to Daniel Ricketson, in The Writings of Henry David Thoreau, 1906

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