ROLLAND LAB - Wildlife Ecology
Bluebird Trail
Lab
Nest Box Monitoring
Prepared by Gunnar Muckelberg and Virginie Rolland
Preface and resources
The 6 commandments of a good bluebird nest box landlord/monitor
Our Bluebird Trail (and nest box types)
What tools do you need to monitor?
What may you encounter in nest boxes?
How to prevent or reduce predation?
How to control for House Sparrows?
Preface and Resources
You may have nest boxes (i.e., bird houses) in your yard or neighborhood and you would like to monitor the success of your guests. Everyone has a different way of monitoring and here we present the Rolland Lab’s monitoring protocol. You may want to compare with other sources and see what works best for you. Here are a few sources for you to consider:
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Sialis website for all kinds of information about nest monitoring but also about the history and the biology of bluebirds and other cavity nesters, nest box building plan, types of predator guards, house sparrow control, and bird baths and food (through native plants or bird feeders).
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Virginia Bluebird Society website where you can find a protocol but also monitoring sheets ready to print and use.
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The Bluebird Monitor’s Guide book by Griggs, Berger, and Kridler (2001)
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North American Bluebird Society factsheets: one is specifically for monitoring , whereas the other is if you’re starting from scratch and also need information about setting up a trail and building nest boxes and predator guards.
If you’re new to this, I really recommend the last two sources. Without going into details, I would just stress this: place your box at least 5 ft off the ground on a pole in open short grass areas (mowed yard, hay fields, pastures, road sides with low traffic) with high perching options (trees, telephone wires, etc.). Do not fix your box on a telephone post, tree, or fence post. Those boxes are easily accessible by all bluebird predators. Similarly, place them maybe 2 yards away from fences and bushes so they’re not within reach of a jumping squirrel.
Back to Eastern Bluebird Main Menu
The 6 Commandments of a Good Bluebird Nest Box Landlord/Monitor:
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You shall maintain it or take it down. A poorly managed box can be detrimental to bluebirds.
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You shall not collect anything (bird, egg, feather, or nest material). This is against law according to the Migratory Bird Treaty Act.
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You shall keep your cats indoors.
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You shall accept all species. Other bird species than bluebirds may nest in your box, accept them. Flying squirrels may also use your boxes to reproduce or store food like acorns. Accept them. Some species of flying squirrels are endangered. The only species you should not accept are European Starlings and House Sparrows because they are invasive species introduced from Europe. If your box is designed with the correct hole size (see below), you will not have to worry about starlings because they are too big to enter the box. House sparrows are small enough to remain a threat. However, you may want to check with your local bird society such as Audubon because some populations of house sparrows are declining.
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You shall not disturb unnecessarily.
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You shall take detailed notes. Your notes, as trivial as they may seem, are valuable!
Why do we Monitor Nest Boxes?
Overall, the long-term goal is to keep track of the population and detect any population decline as soon as it happens. Bluebird populations across their range suffered dramatic declines in the 20th century as a result of DDT, the introduction of House Sparrows and European Starlings (which competed against Eastern Bluebirds and other native passerines), a series of severe winters, and land use change. A nest box implementation program helped the populations rebound and we want to keep this conservation program a success story.
How does Monitoring Help?
Monitoring helps address problems as soon as they occur. It helps detect signs of parasitism (e.g., blow flies, black flies), diseases (e.g., avian pox), predation, competition with House Sparrows, etc. Therefore, we can better prevent by controlling House Sparrows, placing predator guards, conditioning or spraying the nest box appropriately. Monitoring also helps determine when to clean a nest box to prevent spread or survival of parasites before the next nesting attempt. As part of monitoring, we can also observe changes in the landscape that may be a cause for nest abandonment or on the contrary may attract new pairs.
Only though monitoring can we know if a nest box needs some kind of repair. A poor nest box can be what we call an ecological trap. It attracts bluebirds because it’s available, but the bluebirds will be more likely to fail because the box is not adequate. For example, the roof may be broken and the chicks will die of hypothermia with the first rain; or the entrance hole has been enlarged by a squirrel and a European Starling that can now access the box will kill the bluebird chicks to start its own nest.
Finally monitoring means data, which are crucial to determine population trends at the local scale of your trail but also at the species level across its range.
Our Bluebird Trail
Our trail consists of over 150 nest boxes outside the city limits of Jonesboro, AR. They are placed on private and public properties, and include hay fields, cow pastures, yards, and roadsides. Boxes are around 100 m apart. Closer than that, they would be within the same pair’s territory and would never be occupied at the same time. For convenience, our boxes face open areas, but if possible for Bluebirds, make them face East.
Several nest box style exist. You can find more information about the pros and cons of the different styles at the Sialis website.
We use a NABS-style nest box that opens upward from the side. A roof opening allows for nicer pictures but it is easier to clean a nest box with a side opening.
The entrance hole is the recommended standard 1.5” in diameter to exclude European Starlings. Most have a generous overhang to handicap curious raccoons and cats, ventilation slots on each side to keep chicks cool in the summer, two nail-sized holes drilled in the floor for drainage, and a nail to lock the side door.
We have flashing stapled to the roof to prevent rain from leaking into the box. For boxes whose entrance hole has been enlarged by squirrels, we tack metal plates with a same size hole. Our boxes are made of cedar, which we found to be a more durable wood than pine for example. Other people report having more success with other types of boxes like the Gilbertson which is made of PVC. In addition to boxes that we set up, the trail also contains boxes that landowners chose and these vary in style, dimensions, and wood, although all are one-round-hole NABS-style boxes.
If you are a resident at our study site and we already monitor one or more boxes on your property, you can help by:
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Reporting to us anything abnormal you observe.
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Avoiding checking the box yourself. Since we are already monitoring them, this adds unnecessary disturbance. However, we are happy to show you eggs or chicks for you to take pictures when we are around. Just let us know.
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Trimming bushes and mowing your lawn from time to time. Your yard does not need to be manicured, but bluebirds are more successful finding food when the grass is short.
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Contacting us before altering the current set up (e.g., moving a box to another spot, taking a box down, storing hay stacks near a box). We are ready to help to minimize the disturbance if the box is occupied. If you need us to take a box down for whatever reason, please let us know. We can reuse boxes and predator guards and it would help us save money if we can the equipment back.
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Offering your driveway to park our car while we check a box or process a bird.
Please contact us if you have any questions. We will be happy to share what we know about bluebirds with you. We also create a short newsletter at the beginning of every season with some summary statistics of the previous nesting season (e.g., number of chicks produced) and our information (including a picture of our car). If you do not have a junk/newspaper mailbox, but would like to receive our newsletter, contact us and we will deliver it into your regular mailbox.
What Tools do you need to Monitor?
The typical toolbox may vary depending on the data taken and site conditions, but here are a few of the basics.
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Mechanics mirror – This is particularly helpful for seeing into higher boxes but can always be used to determine nest status and count eggs/chicks.
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Pencil – A no-brainer: you need a pencil to record your observations.
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Notebook or data sheet – You may want to keep your own journal, or have a nicely designed data sheet with all the fields you want to remember to fill out. Either way is fine. Datasheets can be downloaded from the Michigan and Virginia Bluebird Societies.
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Brush – Although an old nest may be reused, it is wise to clean it out once the chicks have fledged (i.e., left the nest) or after an unfortunate fate (abandonment, starvation, or predation). This will minimize chances of parasitism.
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Nails – Not only is it not a bad idea to keep a few nails with you to replace the ones you may drop and never retrieve, but nails are also very useful to unplug the drainage holes and scraping dried feces off the walls.
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Spray – A mud dauber will not cause harm, but paper wasps might kills chicks with their venomous stings. Therefore, when wasps are observed in nest boxes, it may be a good idea to spray them. We recommend the organic brand Safer® that is supposedly safe for birds. Still, if the nest box is occupied by a bird, make sure not to spray the birds. You can try to remove wasps with a stick too. If you are allergic to these wasps’ venom, make sure to carry some Benadryl with you and seek medical help if needed.
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Ivory soap – Before each nesting attempt, you may want to apply soap to the roof of your box. We found this technique to be not so effective when the wood wasn’t smooth. The idea with the soap is to make the roof so slick the wasps cannot attach their nest.
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Binoculars – Mandatory only if your monitoring includes banding and adult resighting, they remain a nice option for your observations of parental behavior.
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Camera – Also optional but so convenient to document something unusual or simply to keep some memories.
Additionally for yourself:
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Sun stuff (sunglasses, sunscreen, sun hat)
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Water bottle
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Insect repellent
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Baby wipes or Hand sanitizer to avoid disease contamination or spreading parasites among nests
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Paper towel just in case…
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Cell phone in case of an emergency.
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Long light-colored pants tucked in socks and rubber boots – Three purposes: (1) it will force ticks to go up on the outside of your pants and it will be easier for you to spot them on light-colored fabric -- Don't forget to check yourself in the shower, though; (2) if you accidentally step on a non-venomous snake, the bite will not be as bad (more about snakes later); and (3) you never have to worry about crossing a small running creek or a swampy cow pasture.
What may you Encounter in Nest Boxes?
We mentioned wasps and snakes, but you signed up for bluebirds. So, what creature may you possibly encounter in nest boxes? You might as well get ready for everything...
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Eastern Bluebird: your target!
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House Sparrow: your enemy!
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Tufted Titmouse, Carolina Wren, Carolina Chickadee: the most common native birds that may also be interested in nesting in your nest boxes in Arkansas…
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Tree Swallow, Blue Grosbeak, White-breasted Nuthatch: we recorded only one instance of each of those species but they did occur!
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Flying Squirrel: they can carry diseases such as rabies but they are native, so leave these cuties alone. They reproduce twice a year and nest in cavities such as nest boxes, but may also use nest boxes as a storage room for their acorn collection.
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Bats: Evening and Big Brown bats have been common occurrences in nest boxes over the past two years. They usually don’t hang out in a box already occupied. They will only roost there for the day and leave. So far we have not seen the same box used more than twice and not the same day. Bats are a precious natural pesticide, so leave them alone too. Take a picture and close the box.
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Gray Treefrog, Green Treefrog: You can move them to a tree nearby or leave them there. They don’t really stay.
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Ants: They can be problem. Clean your boxes well. You may want to apply a ring of grease on your pole to prevent ants from getting to the box. Thankfully, in our region, we do not yet have Red Imported Fire Ants; they can kill chicks.
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Ladybugs: The Asian kind will overwinter in colonies in some corner of your boxes but they leave when the weather gets warmer.
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Mice: Similarly to ladybugs, they only use the nest boxes during the winter. To prevent mice from using the boxes, you need to keep the box open or take it down; but then, bluebirds cannot use it for winter-roosting either. We decided to “winterize” (see below) our boxes for bluebirds because we rarely have mice. The cost-benefit balance was weighing heavily for keeping the boxes usable for all rather than closed to all.
What do you need to Record?
The information below is a summary but each stage is detailed later.
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Box number (if any)
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Date of each visit
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Species
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Nest stage
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none,
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start,
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complete: nest material,
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egg laying: color and possibly size,
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incubation: number of eggs,
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hatching: estimated or exact date, number of eggs that hatched,
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rearing: number and possibly age of chicks
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Fate
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Fledged: number of fledglings
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Abandoned (cold eggs, chicks cold, underdeveloped, or dead)
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Depredated (raccoon, cat, squirrel, snake)
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Attacked by house sparrow
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• Any parental behavior (dive-bombing, calling, etc.)
• Other observations (including weather)
Monitoring Protocol
Ready?
Typically, nest boxes should be checked weekly and ideally in the afternoon (before dusk). Data sheets provided by the Bluebird societies are even designed for a weekly check. Bluebirds are very tolerant of humans so you may visit the boxes up to twice a week, but more often can be a disturbance or worse attract predators. Females usually lay their eggs in the morning, which is why it is best to check in the afternoon. Disturbing a female in the process of laying an egg increases chances of nest abandonment. However, if adult resighting is part of your monitoring (see advice below) or if you’re interested in recording parental behavior, nest box checks are best done before 11 am because adults are more active caring and provisioning their young during that time. Also, although weekly monitoring is typical for bluebird trails, a more accurate picture can be gained, if you want the exact date of hatching, with a modified schedule. Because our research requires exact hatching dates for adult and chick banding, our protocol deviates from the standard, as follows.
At first, we do only check the nest boxes once a week, like the standard monitoring protocol. Based on what is found, the schedule might change. To announce yourself and give a chance to the female to leave the box if she is inside, talk, whistle, or sing, and knock gently on the side of the box. Do not remain in front of the box to avoid a collision with an escaping bird!
Remove the nail that keeps the door shut and open slowly. Then, have a peak into the box. If empty, pretty easy, but if there is something, use the mirror to have a better look. Below are the different stages you may find:
Empty – If a box is empty, record and check it again in a week.
Twigs – A few twigs does not mean a nest. A bluebird male that has selected and is defending a box as part of his territory commonly place a couple twigs in the box as a display. These twigs may be small sticks, pine needles, or pieces of short dry grass. If a close-by female “likes the display” and chooses the male and his territory to settle, then she will begin to build a nest in the box. Because, twigs do not mean nest, a box with twigs can be checked a week later like an empty box.
Note: Males in other species may also use a display. At this point, it is difficult to determine the species. Chickadees and titmice may leave a little clump of moss, whereas House Sparrows, Carolina Wrens, Tree Swallows, and Bluebirds will use grass or sticks.
Start – A start usually has the shape of a nest with nest material on all four sides of the box, but the nest has no depth or cup and in its center, you can see/feel the bare floor. Check in four days. Females take more time to build a nest at the beginning of the season (late February – early March in Arkansas) than for their subsequent nesting attempts later in the season, but there is variation among individuals and we do not want to miss a complete nest with possibly eggs.
Note: At this point, you might be able to identify the species. So, it’s time for us to review the material and shape of each species’ nest. For additional help, I recommend Nests, Eggs, and Nestlings of American Birds by Baicich and Harrisson (2005).
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Eastern Bluebirds have nests that are primarily composed of pine needles or straw. They form a cup in the back of the nests to house the eggs. The cup is frequently lined with cow or horse tail hair, and sometimes the female adds feathers. The nest can be as shallow as 1.5” and as tall as 6” but it is always a compact cube with the cup open at the top. Caroline Chickadees and Tufted Titmice also build their nests in the same general shape.
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Carolina Chickadees have nests that are almost exclusively made of moss, although the nest cup will be heavily lined with animal fur. Once they lay eggs they bury them within the moss. These are loose spring nests.
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Tufted Titmice have nest similar to the Chickadees, but if you pay attention, you’ll notice leaves and maybe shredded bark intertwined with the moss. The general color impression is a brownish light green, whereas chickadees’ nests are a dark moss green.
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Carolina Wrens’ nests occupy the entire space of the nest box with a tunnel (from the entrance hole) that leads to the cup inside this “den” made of pine needles, straws, and leaves.
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Tree swallows’ nests resemble those of bluebirds in material and shape, but are always lined and topped with quite a few feathers.
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White-breasted Nuthatches build compact nests of the same shape as Tree Swallows and Bluebirds, but their nests are made of shredded bark, pieces of wood, and fur.
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House Sparrows, our invasive species, form nests with straws and pine needles, like Bluebirds, but they frequently include human products as well like pieces of plastic or cigarette butts. Like the Carolina Wrens, their nests fill up the entire box. If you find a House Sparrow nest, control for it. See our House Sparrow control section.
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Flying squirrels build a high compact nest made mostly shredded bark and fur. If the nest is occupied, the female and her offspring will be sleeping in the center of the nest – this is a nocturnal species that looks for food from dusk to dawn. You cannot see them. If you want to make sure the squirrels have not vacated the nest, you may use a long stick and poke gently into the nest. When mom is disturbed, the nest moves, and she may stick her head out. Remember in spite of their cute faces, they are wild animals and may bite if feeling in danger. The stick method should be used with caution. What I found fairly reliable is a good observation of the nest. If the nest is really tall, taking up most if not all the space of the box, it is likely occupied. And the earlier in the season it is, the more likely it is occupied. When squirrels vacate the nest, the nest tends to shrink and may take half to three-quarters of the box space. Sometimes, we can even see where the cup was. May–July are months during which squirrels are unlikely to nest with babies. When you’re ready to clean a flying squirrel nest, you need to be sure it is unoccupied or you may discarding a nest with hairless, blind babies. The nest will have accumulated possible rain but also urine and feces, so, when you do clean it out, scrub the box thoroughly.
Complete – A tightly woven nest with a defined cup lined with horse/cow hair or feathers is considered to be complete and can be checked every two days. If the nest is still loose, the cup is not well defined, or a small area remains bare, it is not complete and can be checked as often as a nest start (i.e., every 4 days). Nest height varies and does not define being complete. As a matter of fact, females, though rarely, may lay eggs on the bare floor.
Eggs – Eastern Bluebirds lay up to 3–6 eggs in one clutch, and they normally lay them a day apart. Use your mirror to determine the color, shape, and number of eggs in the nest. If you forgot your mirror and the nest is too high for you to see, do not remove the nest out of the box. You risk dropping eggs. Instead, you may, with a very light touch, feel for the eggs. You can determine how many are present by rolling delicately the pulp of your fingers over the eggs. Birds see and hear better than we do, but their sense of smell is poor, so touching the eggs will not drive the female away. This is no reason to handle the eggs unnecessarily, though! Also, make sure your hands are clean and dry before you do this.
Bluebird eggs are mostly blue ovals, but some females (up to 9%) lay white eggs and even more rarely (1%) they may lay pink eggs. Also, check the size of the eggs. They should be about the size of a nickel. If bigger, they may still hatch, but if much smaller, they are infertile.
Above: Found on the Internet. Right: two cases at our study site (normal with dud and elongated)
How about other species? Titmice, chickadees, and wrens lay smaller eggs with pinkish brown speckles. House Sparrows lay eggs of about the same size as Bluebirds but are white covered with dark brown splotches. Tree Swallows have longer white eggs.
Also, look for eggs that look foreign, i.e., eggs larger with small brown spots. These are eggs of Brown-Headed Cowbirds, a native species that lay eggs in the nests of other species. This reproductive strategy is called brood parasitism and this is only way these cowbirds reproduce. If you find such eggs, monitor them, but do not remove them; it is illegal. They will likely hatch before the others but it is not impossible for all chicks to be raised successfully.
If you need to know the exact date of the onset of incubation, you may check every other day to determine the last egg date, which is also generally the first day of incubation. Otherwise, you are fine checking every 4–7 days.
Onset of Incubation – Incubation starts with the last egg laid. To tell if a clutch is being incubated, a light touch can give you an indication of the eggs temperature. If incubation has started, eggs will feel really warm even on a cold day. From the last egg laid, count 11 days. This will be the earliest possible day of hatching as Bluebirds incubation lasts 11–14 days. Alternatively, if you know the date of the first egg but not that of the last, you can add the date of the first egg laid to the total number of eggs plus 11 days. So if the first of April was the first egg date and 4 eggs were laid, the estimated hatch date would be 1+4+11 = the 16th of April. Check only once half-way through incubation to ensure the nest is still active. No need to check more often; ït causes more disturbance than necessary with a risk of nest abandonment and there is no information to be gained. Although the length of the incubation period varies among species (see Table below), the same schedule can be followed.
Middle of Incubation – Count and feel the temperature. Warm eggs are a good sign; come back at the estimate hatch date. If the eggs are cold and you do not observe any sign of parental activity around the nest, eggs may have been abandoned. Check in a couple days. If the eggs are still cold and adults are nowhere to be seen, the nest may have to be discarded. You may want to check one more time 2–3 days later before deciding to toss it away from the box, especially early in the season, when females sometimes decide to hold incubation for a few days if it is too cold. Eggs can survive a few days without being incubated. If the eggs are gone, your nest has been depredated. Look for signs that may indicate the culprit species.
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Egg shells and nest not disturbed: likely a squirrel
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Nest disturbed (with or without egg shells) if not even pulled through the entrance hole, with maybe scratches on the box: sign of a raccoon or a cat reaching into the box. In such case, you may want to increase the size of the overhang part of the roof and/or add a Noel guard.
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Nest undisturbed and no egg sign: likely a snake.
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A coiled snake: well obviously… In such case, the snake, digesting a full meal, is likely harmless. You can choose to wait for the snake to leave on its own or remove it yourself. Neither Black Rat Snake nor Speckled Kingsnake are venomous snakes, but use caution nonetheless. You may be angry that it ate your dear guest’s eggs, but they are both very beneficial to have around; rat snakes because they keep mice and rats away from your house and kingsnakes because they eat other snakes including the venomous copperhead.
Hatching – Check for pipping eggs or hatched eggs at the day of the estimated hatch date. Come back every day until eggs hatch and record the date if you are not tied to a strict weekly schedule. Otherwise, count the number of chicks and estimate the hatch date based on the size of the hatchlings (see aging guide). The day of hatching is typically noted as DAY 1. Hatchlings are blind and featherless with the exception of a few gray, wet tufts -- The tufts are darker in bluebirds than titmice. All eggs should hatch within 24 hours. Once the eggs have hatched, you may visit the box only in one week (DAY 7) to check that they are still alive and growing normally.
As part of our monitoring protocol, we spend time resighting parents with binoculars. If they were previously banded, we record their ID, which is made of a USGS aluminum band and three color bands in a unique combination. We use 6 different color bands to create these unique combinations: White, Hot Pink, Yellow, Orange, Lime Green, and Green. Their ID is determined by the left leg then the right leg by noting the color of the bands from top to bottom. If a parent is not banded, we would come back the following day (DAY 2) to capture, band, and measure them. Note that capturing and banding can only be done with proper federal and state permits. See below for more information on trapping and banding and how to read their bands. If you ever find a dead bird with a band, report it to USGS to this link. You will receive a report of the bird’s story and a certificate for reporting the bird.
This male bluebird ID is read XGGG. The X band is the USGS metal band and is the top band on the left leg of the bird. G stands for Green.
USGS certificate sent to Mr. Nicholls after he reported the band number of a dead Gray Jay he found in 2002. With this certificate, Nicholls learned that this bird was actually born in 1985, making it the oldest known Gray Jay!
Young chicks – Check that the chicks are alive. If alive, count them and record your observations of their growth. Make note of any begging behavior. Are they cold or lethargic? Are their eyes open? Can you see tiny feathers pointing out? Are the parents around, maybe dive-bombing you? ––Don’t worry, they’re trying to intimidate and make you move away from the box. They rarely touch but even if they do, they don’t hurt.
If only one chicks seems less developed than its siblings, it’s ok.
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If all chicks seem cold, lethargic, hungry, see if there are signs of the parents. If no parent and the situation seems critical, you may want to bring the chicks to your wildlife rehabilitator. If the chicks seem cold but healthy, they have gotten wet during the last rain event and risk hypothermia. Check if the nest is wet. If so, you may want to replace the nest with a clean old one. If you do not have an old nest handy, you may pack dry grass and pine needles and offer some mealworms.
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If you observe black flies, spray around the box but not inside. If you find a blowfly infestation, remove the nest, clean the box, and place a new nest. Similarly, if you find ants, remove the nest, clean the box, and put the nest back.
These are tips to help bluebirds, but if your interest is only to provide a nesting cavity and to observe Nature at work, that’s fine too.
Candice is being dive-bombed. You can see a little blue winged thing above her pony tail.
Chick bruised with black fly stings.
If not all chicks from DAY 1 are present, try to determine the cause:
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One or more chicks is dead of the nest: may be because of starvation or hypothermia. If the nest was parasitized by a cowbird, the cowbird chick may have been able to claim all the food brought by the bluebird parents. Remove the dead individuals so that the rotten smell does not attract predators. Similarly, if there are eggs that never hatched, remove them.
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All chicks are dead in the nest: may have been abandoned because of the death of one or both parents, or because food is limiting. Dispose of the nest and chicks as far away from the box as possible to avoid attracting predators when a new nest is built. Clean the box.
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Body parts with or without chicks still alive in the nest: squirrel predation. Remove the dead parts from the nest.
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No chick in the nest and nest is disturbed: raccoon or cat predation. See Incubation.
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No chick in the nest and nest is undisturbed: snake predation. See Incubation.
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A coiled snake. See Incubation.
Squirrel depredation: soon after hatching (chicks are still featherless), blood traces and one chick missing its body (only head remains). Raccoon depredation: nest material and feathers pulled out of box. Snake depredation: recent meal as the snake is still resting in the box.
If at least one chick is alive, your next visit should be on DAY 13 at the latest. This is very important. Later than that, chicks are alert enough that they may attempt to leave the nest prematurely if disturbed. However, they may not be developed enough to fly and will be very vulnerable once out of the nest. We would even recommend to stop checking earlier for nests of Carolina Wrens as their development is slightly faster.
Older nestlings – The same observations as for the younger chicks can be noted. At this stage, chicks should have small feathers out of their pins and well opened eyes. As part of our monitoring, we band and measure chicks on DAY 13 (See below). The same kind of conclusions using the same observations and signs can be made. The final check should be made after the expected fledging date. Generally, it is safe to check on DAY 18 because a chick that fledges in front of you at this age is capable of flying to the closest tree.
Fledging – Open the box carefully and quietly. If there are still chicks in the box, count the best you can without too much disturbance. Check every day until they have all fledged. Once gone, make notes of what you find, and then brush the box, use the nail that keeps the door shut to clean the drainage holes and to scrap off dried feces from the walls of the box. Not only is this helpful, as explained previously, to minimize parasites such as feather mites, flies, and even ants, but it will also make your life much easier to detect the beginning of the next nesting attempt. Bluebirds are called multibrooded species, which means they can raise more than one brood per season. Depending on the region, Bluebirds lay 1 to 3 successful clutches a year, between March and July. At our site, we recorded 2 pairs in 2016 that reared 4 batches of babies. This is very unusual and needless to say their last protégés fledged around mid-September.
What to do with the nest? If it looks filthy (see picture below), discard as far away as possible from the box to avoid attracting predators. However, if it looks clean, shake the dander off, freeze it for about 3 weeks and you can place it back in a box when the nesting is over. Bluebirds are more likely to use a box for winter roosting if it contains an old nest. Alternatively, at the end of the season, if you do not have clean old nest, you can also pile dry grass and pine needles in a nest shape (without the cup, don’t worry!). Bluebirds will still be happy to use those over an empty box.
Left: Fecal sacs and leftover food (millipede and grasshopper). Right: floor covered in dander and semi-fresh fecal sac stuck to the wall.
Left: nest infested with mites (For mites to still be active in nest, chicks left recently). Middle: nest infested with ants (White eggs everywhere). Right: filthy nest flattened with chick waste (Mom did not do a good job with her offspring's hygiene).
Among your notes:
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Disturbed nest? Same as any other stage, a disturbed nest partially or completely pulled out of the box is indicative of raccoon or cat predation.
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Undisturbed nest? At this stage, an undisturbed nest either means chicks fledge or that a snake got there first. This is why it is important to record as many observations as possible to determine the fate of the nest.
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Parental activity? If parents are still around, emitting distressed calls or dive-bombing you, there is a good chance that their young recently fledged. They are worried you might find them and attack. The young are usually hiding in trees and you may not be able to see them… maybe in a few days when they feel more comfortable with their new flying skills.
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Any leftover food? Bluebirds provision their chicks with a range of insects including beetles, crickets and grasshoppers, moth and butterfly larvae, but also spiders, snails, lizard tails, slugs, and earthworms.
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Any fresh or semi-fresh fecal sacs? Chicks’ droppings come into a little white sac that mom can pick up with her beak and discard away from the box. Any fresh fecal material is a good indication that chicks have very recently fledged.
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The amount of dander. The more dander, the bigger the chicks before they left the nest.
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Flattened nest? Remember the nice cup of the nest when freshly completed before the female her eggs? Well, oftentimes, especially with a brood of 4–6 chicks, the cup does no longer resemble a cup and the whole looks flat. This is another sign that the chicks have had a chance to successfully fledge, although it is still possible that a snake snatched them a day or two before.
How to Prevent or Reduce Predation?
As mentioned, common bluebird nest predators include snakes (mostly Black Rat Snakes, but also Speckled Kingsnakes), raccoons, (flying) squirrels, and feral cats. You can even but seldom have birds of prey get to boxes. Snakes climb up the posts or poles and go through the entrance hole or ventilation holes if they are big enough. They characteristically take all eggs or chicks that are present. Raccoons and cats either climb up or jump on and reach inside with their paws. If an egg falls to the side or a chick squeezes in the back as mammal pulls the nest, the hunt may not be 100% successful.
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To help lower levels of depredation a few different guards can be considered:
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Messy and not perfect, axle grease can be applied on the pole in a thick coat from the base all the way to just under the bottom of the box. Ants get stuck and raccoons lose their grip and slide down, but a strong, long, and hungry rat snake will not abandon easily and will still be able to reach the box. If so, the snake will leave slithering tracks on the grease and you will see grease on and maybe inside the box. Also, grease is not recommended if you have domestic animals, especially those that sometimes like to rub against poles such as cows and horses.
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Any baffle: cone (expensive but effective), PVC pipe, or Kingston stovepipe (cheaper and effective) below the boxes. The cone blocks snakes, cats, and raccoons. PVC and Kingston block the snake that climb along the pole inside the pipe, whereas it destabilizes raccoons and cats and raccoons, provided that the pipe is set to wobble properly. The Kingstone stovepipe with his hardware cloth top has the benefit of keeping the snake interested as this mesh does not block its sensing of sight, smell, or heat emitted by the chicks. The goal is to have the snake go in the pipe rather than around. I recommend against lethal guards because as explained earlier non-venomous snakes are actually a good thing to have around. Also, unless you get rid of the snake quickly, a snake trapped dead is still a snake and the bluebirds will not go back into the box if they see it, leaving their chicks die of starvation. That kind of defeats the purpose, right?
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Noel guard: PVC or better hardware cloth tunnel creates an extension at the entrance hole that will be longer than a raccoon or cat’s limb s that they cannot reach in. The disadvantage of this guard is that it will attract House Sparrows. These birds love perches right at their nests.
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Large overhangs help against raccoons and cats reaching from the top.
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The best guard against cats is to keep your cat inside your house. Even if they don’t reach in the box, they may still snatch the parents while they pick up an insect on the ground. If you’re allergic or have another odd reason to have an outdoor cat (who may still risk his life around cars and nocturnal wildlife), fit them with a colorful collar. You can make your own or order one from Birdsbesafe for example.
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To limit cat and raccoon predation (but not snake and squirrel), I would remind you to place your box on a pole (no fence post or telephone pole, or anything that provides traction for a climbing predator) away from bushes, fences, and overhanging branches.
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One way to decrease likelihood of depredation is to not create a scent trail. So, try to use a different path every time you approach the box. The same path over and over can lead a predator right to the nest.
For more information, including plans to make those guards, check the Nest Box Builder website.
How to Control for House Sparrows?
House Sparrows are an invasive species that can kill bluebirds. They will first peck at the eyes of their target bluebird so they are rendered defenseless. Then, they will peck elsewhere to death. House Sparrows may also kill chicks and puncture bluebird eggs. There are different methods of control.
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Passive methods
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Avoid placing your box close to buildings. House Sparrows thrive around humans.
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Use deterrents: Whatever deterrent (fishing line, colorful or shiny spookers), House Sparrows will eventually learn they are not threats and will use the box.
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Dump the nest: You may remove every nest they attempt to build. They will be relentless and will try again and again, and the box will not be available to other birds until they abandon their efforts.
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Shake the eggs energetically: Once all eggs are laid, shake them. Shaken eggs are infertile and House Sparrow parents will incubate for much longer than needed, keeping them busy. Again this does not make the box available to other bluebirds, but at least they are not attempting to reproduce elsewhere.
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Active methods
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Some people shoot House Sparrows with a BB gun.
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Live trapping with a Deluxe repeating sparrow trap.
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Humane euthanasia after trapping them during incubation with the same trapping method used for Bluebirds.
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For more details about House Sparrow control, check the Sialis website.
Bluebird trapping and banding
As mentioned, we band both adults and chicks for future identification so we can estimate survival over time and monitor fluctuations in the population.
Adult Trapping – On DAY 2, we attempt trapping the adults to band them for future identification. This helps us estimate their survival probability from year to year. Again, these activities require federal and state permits, proper training, and must be approved from an animal ethics committee. Do not follow this protocol if you are not trained, authorized, and in compliance with
laws of animal care and use. Most songbird biologists use mist-nets to catch adults. However, Bluebirds are high flyers avoiding the nets. Therefore, we trap them directly at their nests using a trap designed by Robinson and Risch (2006). Nothing fancy, the trap consists of a little square of hardware cloth that we duct-tape to the inside of the box and that we prop up with a straw. The parent going into the box to care for their young will knock the straw and the square will spring back behind them trapping them inside with their hatchlings. Every box with a trap set is checked every 5–10 min. When a trap is down, we slowly slide a hand inside the box, keeping all spaces blocked; we seize the parent in the proper grip and put it in a clean cloth bag. We reset the trap in hopes of catching the other parent and we move with our bird to a safe distance to ensure that the other parent is not kept away from the box and can still go feed the chicks without worry. Once the bird is banded and all measurements taken, we bring the bird back close to its box to release it.
Adult banding – While the bird is still in the bag securely tied, we weigh the bird with a Pesola scale to the nearest 0.5 g. The bird is placed in bander’s grip* and we weigh the bag without the bird. The difference constitutes the bird’s mass. We keep the bird in bander’s grip with its head still in the bag to keep the bird as calm as possible – dark has a calming effect. If the bird is a chick from another year then its USGS band number will be recorded. If it is not a USGS band will be attached to one leg; this is done first to ensure that even if the bird escapes now it will be identifiable by its USGS band. We use butt-end bands that are applied with special pliers*. Next, combinations of colored bands are applied with small shoe horn-like devices. Color bands designed specifically for birds exist but they are not cheap. Bluebirds’ band size is luckily the same as color beads you can buy in big bags of 500 of more beads. In the lab, we prepare all the color bands by making a neat radial longitudinal cut. The shoe horn-like device opens the band that can be slid onto the bird’s leg. We use a unique combination of color bands (Figure). The bird is then aged based on the presence or absence of a molt limit (Figure), sexed, and measured for wing chord* and tail length*. We also assess its health looking for mites, pox, or any abnormalities, and determining its fat status*. Once the bird is released, we sanitize our hands and we use a new bag for the next bird.
*For detailed information on how to perform these measurements, consult the North American Bander’s Study Guide.
Top: Male has a recurved beak, whereas female has legs and feet covered with avian pox-related growths. They were both successful, though. Right: Aging bluebirds. Young males (SY) have a clear molt limit, not adult males (ASY).
Chick banding – On DAY 13, we band the chicks. This is not a strict time; other people band as early as DAY 9 and as late as DAY 15. Chicks being chill in their nest, this only requires a simple hand capture. Again, no matter how simple this may sound, the process requires a permit and an approved protocol. For chick banding, we stay close to the box so as not to tempt the parents to visit their nest while empty and risk abandonment. Banding the chicks is very similar to banding the adults, but chicks are only given two bands instead of four: the USGS band on one leg and a color band on the other. Their legs tend to be not as long as those of adults. In our protocol, the color is chosen to be the same for all chicks born the same year. If they are resighted in subsequent years, we can easily tell when they were born. If we recapture them as adults, we give them a full 4-color combination. Because chicks of the same nest live together, there is no risk of spreading a new disease from one chick to another. Therefore, we keep all chicks together in one bag, which is likely advantageous to them. If your siblings are with you during such stressful experience, you’re likely less stressed than if you’re by yourself. The first chick is placed into another bag to measure its weight before we band it and take its measurements. Because the tail feathers of a chick are not fully grown, we measure the tail
length differently from the adults: we slide the ruler between the outermost tail feather and the others to simply measure that outermost rectrix. Like for the parents, we also check for abnormalities and presence of mites, and we sex the individuals. The flight feathers, as small as they are, already show sexual dimorphism with fairly bright blue feathers for males and duller, greyish feathers for females. Once processed, the chick is put in a third bag. The process is repeated with all siblings before they are finally returned to their nest. If the parents are noticeably stressed, the first banded chick will be returned to the nest immediately. A parent with only one surviving chick is still dedicated and happier than if it lost its whole brood. Once returned to their nest, we sanitize our hands. It is not necessary to sanitize them between siblings as they already share parasites from their nest.
Finally, if you’re really into this, consider reporting your data to citizen science programs such as NestWatch.
