Apr 11, 2018 | Featured in: Watching Backyard Birds, April 2018

Top Ten Nest Box Tips

A female eastern bluebird perches on top of a nest box. Photo by Bill Thompson, III

So you want to be a landlord to the birds, eh? Well, it's not as easy as falling off a log. It's no accident that the most diligent landlords often have the highest rates for fledging healthy young birds. The good news is that diligence as a bird landlord need not be painful or overly difficult. Below are my Top Ten Nest Box Tips for backyard landlords.

10. Spring cleaning. Now is the time to get busy with cleaning out your boxes, if you haven't done so already. In some areas, you may find that March or even February is not too early. Sweep all the crud out of the box (making sure it's not this year's nest, of course). If it's still a little grungy, give the box a rinse out with a 1:9 bleach–water solution, using a scrub brush or an old toothbrush if necessary. Rinse well and let the box air dry before closing the entry. There's no need to place any nesting material inside the box in spring; the birds prefer to do that themselves.

Is it really necessary to do this? After all, natural cavities don't get scrubbed out each spring. That's true, but an empty next box is more likely to attract a tenant than one that's full of crud, and the box will be a clean and healthy space.

9. Maintenance and replacement. Spring is also the time to repair damaged or worn boxes. I take a Leatherman utility tool with me for tightening screws, bending metal baffles back into shape, and pounding loose nails. Sometimes a box is too far gone and must be replaced. This is the perfect time for an upgrade to a better box, a different design, or a box for a different tenant.

8. Right box, right place, right hole. There are nest boxes that go years without tenants. If you have one of these, your problem could be the box's location. Bluebirds and swallows prefer to use boxes in open grassy areas. House wrens, Carolina wrens, chickadees, titmice, nuthatches, and woodpeckers prefer boxes near or in the woods. You may also have a box with an improper entry hole size. The ideal universal entry hole is 1½ inches in diameter, although an even smaller hole (1 inch in diameter) is better for wrens, chickadees, and nuthatches. Entries larger than 1½ inches in diameter will permit house sparrows and European starlings to enter. BWD's A Guide to Bird Homes has a complete chart of the proper nest box entry sizes for all cavity-nesting species. Studies have indicated that most box-using birds may prefer their boxes to be oriented so that the entrance is facing east.

7. Predators & pests. The onset of nesting is also the start of nest-predator season. Make sure your boxes are mounted on galvanized metal poles with pole-mounted baffles below the box. Also check to make sure that a predator cannot access the nest box by slithering, reaching, or jumping from a nearby perch. Do not use insecticide or pesticides inside or near your bird houses. If your boxes are raided by predators during the nesting season, do your best to determine which predator gained access to the box and then take steps to prevent a recurrence.

6. Monitoring notebook. The very best way to keep track of your tenants is to keep a watchful eye. Do this by making regular visits to each nest box and recording what you find in your landlord's notebook. A small spiral-bound pocket notebook and a pencil are all you need. Information to record includes: name or number of box (see number 5), date of visit, time of day, weather conditions, contents of box, number of eggs or young, age of young, condition of young, presence of adults, presence of parasites, and anything else you can think of that will be a useful reference for the future. After several years of record keeping you will know and appreciate your most productive boxes and tenants.

5. Numbering/naming. If you have a variety of boxes on your property or an entire trail of boxes, as many bluebird landlords do, it is extremely helpful to name or number and label your boxes. This aids a great deal in record keeping and in helping you remember over the years which boxes are good producers. We've named our nest boxes after their locations on our farm: upper meadow box, spring trail box, far orchard box, etc.

4. Other enhancements. Good landlords know there are certain little things you can do to attract the attention of potential tenants. Most cavity-nesting birds prefer an unobstructed path to the entrance, so make sure that vines and brush do not get in the way. Tree and violet-green swallows use white feathers in their nests, so a handful of them spread across the lawn during nest-building time will entice swallows to use your boxes.

Adult bluebirds always seem to appreciate a snag or T stand that is 20 to 50 feet from the nest box entrance. This serves as a song and hunting perch and as a place that fledglings can aim for on their first flight from the box. Great crested flycatchers love a good snakeskin to pull into the nest box. Purple martins readily take to perches above their houses and to trays of crushed eggshells, which they eat for grit and calcium. Barn swallows and robins appreciate a nice puddle of mud for nest construction materials.

3. Know your tenants. It is important for you to know which species are using your boxes and how long they incubate their eggs. For instance, the time between incubation and fledging for a bluebird and a tree swallow can differ considerably. Check a good reference book or a reliable website for incubation and fledging times of the species nesting in your boxes. Bluebird and purple martin landlords can also rely on the expertise of conservation organizations devoted to these species.

2. Scheduled visits. If you know the dates of your birds' first eggs and when incubation started, you can guesstimate when to visit safely and when to leave the birds alone (near fledging time). A visit to a box full of 13-day-old bluebirds may cause the nestlings to leave prematurely. If you visit a nest and find everyone gone long before the estimated fledging date, you can surmise that the nest met an untimely end. Your familiarity with the birds in your boxes will also help you to know when something is not right, such as when you see an agitated adult fluttering near the entry. Intervention is not as good as prevention in the case of predators. In any case, an empty nest can be cleaned out and readied for the next potential tenant.

1. Compare and share data. As you accumulate more and more data from your nest boxes, it becomes valuable to others. You can become a citizen scientist through online forums such as Cornell Laboratory of Ornithology's NestWatch project. This kind of data can give you a glimpse into the lives of our most beloved backyard birds—those species that are willing to accept our offerings of housing and shelter. We owe them the helpful stewardship of being good landlords.

About Bill Thompson, III

Bill Thompson, III, was the team captain for Watching Backyard Birds from its inception 23 years ago through his death on March 25, 2019. So much of what he wrote is timeless and remains informative, helpful, and inspiring.

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