Quick Tip: Replace a wet or blow fly infested nest by forming a new, cup-shaped nest out of long pieces of DRY grass (not treated with pesticides), pine needles or Timothy Hay you can get at a pet store. Wrap it around your hand and punch down the middle with your fist. Quickly and gently move the nestlings to the new nest. Fix box so future nests don't get wet. Also see Preventing Hypothermia. AVOID a nest change for fully feathered birds (e.g., 13 day old bluebirds) as they may prematurely fledge.
NOTE: Technically, under the Migratory Bird Treaty Act, handling nests or possessing old, used nests is not allowed unless you have a permit. While the U.S. Fish & Wildlife Service may chose not to enforce this requirement for bluebirding monitoring activities, they do have the authority to do so. More info.
Wet nests can result in hypothermia, cause a deadly fungal infection, affect egg hatching, or exacerbate pest problems. Nests may become soiled if parents feed mulberries or earthworms. Blowflies or ants may infest a nest. In these situations, bluebird or Tree Swallow nests can be changed out to protect nestlings. It's not hard, and the nestlings and parents will tolerate it. Do it before the 12th or 13th day after hatching, to prevent premature fledging. You may want to print these instructions to bring with you, so you are prepared and can move through the process as quickly as possible.
It is handy to save unused bluebird nests for these emergencies (note: See The Law.)
A holding bucket (deep enough to prevent escapes), small deep plastic container (e.g., for Cool-whip), shoe box, or grocery paper sack that you will put the existing nest and babies into
A bucket or container for tools
Two old cloth towels or some paper towels
An old paintbrush
A spatula or a putty knife
A rag or sock to plug the hole if nestlings are old enough to jump out in a panic
Replacement nest in a Tupperware/Rubbermaid sandwich container
Fashion a replacement nest out of dry grass (longer grass stalks work best) or pine needles (see nest material). You can use a round or square plastic container (e.g. Cool-whip), or a basket coffee filter to form the nest. Just like the female bluebird, first line the edges with grass (take some tall, dead, dry grass and wrap it around the fingers of one hand), and then place soft, finer grass in the center. (For Tree Swallows, line the cup with feathers.) Punch/smash down the center with your thumbs or fist to form a deep cup that will keep the babies contained and warm. A typical bluebird nest is about 2.25 - 3 or 4" deep, with the cup portion 2.38-2.5" in diameter. The nest should be about 3" below the nestbox entrance hole. Don't make it so high that predators could reach nestlings via the entrance hole, but do recognize that they will mash it down somewhat. The female will fix it if yours is messy.
Gather your tools, and a helper if possible. Take your holding container and open one of the towels out into it. Drape the long ends outside the bucket and push the middle into the bottom. Put the tools in the other bucket. Carry everything out to the nestbox.
Plug the nestbox hole loosely with a rag or sock. Open the box.
Gently stick the spatula or big putty knife under the nest. Cup your other hand over the top of the nest to cover and contain the nestlings. With the spatula under, and your other hand over it, carefully and quickly move the nest to the bucket with the towel in it.
To keep the nestlings calm, cover the top of the bucket with the other towel and move the bucket so you don't trip over it. (Or use a paper grocery sack and fold closed, or shoe box with cover.) Have the helper watch the bucket while you work.
Take the old nest out and put it into the spare bucket. Dispose of the nest in the trash or far enough away so as not to attract predators.
While standing upwind (or wearing a dust mask), sweep out the box with the old paintbrush. Scrape out corners with the putty knife.
Put the new nest into the nestbox.
Carefully pick up each baby and check it over for blow flies, looking under the wings and on the belly. Pull off any larva you find (they come off easily). Gently put each baby (one at a time) back into the nest and close the door. Moving the baby birds to the replacement nest can be dangerous to the baby birds' soft bones, so do not "roll" them.
Leave the rag/sock in the hole for a minute or two (longer if nestlings are older) to allow nestlings to calm down. Then pull it out and walk away. The parents (who may have been dive bombing you and making clicking noises during the process) will go right back into the box.
Material to construct the nest:
If you don't have an old, clean nest and you can't find any dry grass clippings, you can use Timothy Hay, which is available in bags at grocery and department stores that have a pet department (for guinea pigs, hamsters, etc). It is clean and dry and does not contain any herbicide or insecticide or chemicals, which can not always be said for lawn grass.
If you can't find any dry grass/needles, put several handfuls in a bucket and dry them out with a blow dryer.
If you have unused bluebird nests (abandoned before or during egg laying), save them in a plastic baggie for use as replacement nests. Used nests may contain blow fly larvae or other pests, and should be discarded away from the nestbox.
Figure out why the nest got wet:
If the nest is wet, figure out why and correct the problem (best to do this maintenance BEFORE nesting season starts!)
Double check the nestbox to ensure that all box seams (especially if the roof butts into the back) are sealed. If not, caulk.
Adjust the direction of the entrance hole away from prevailing winds.
Make sure the front and back pieces of the box have not pulled away from the sides - if so, screw them together and caulk.
Put a drip edge underneath the roof (a saw kerf that helps the water run to the edges of the roof instead of dripping straight down.)
If boxes have insufficient overhang (2" on the sides, 3-5" in the front is ideal to protect against rain, heat and roof sitting predators):
Put a second larger roof on top, leaving a 3/4" space (using spacers) between the roofs to keep the board underneath from rotting.
Flat overhanging roofs should have saw kerfs (grooves) 1/8" deep and 3/8" back from the roof edge to draw water away.
Put up a 7/16" thick cement board on top of the roof.
Add a piece of wood trim to the front edge of the roof to serve as a drip edge.
After nesting season is complete, coat boxes with linseed oil or SUPERDECK (Coastal Gray color works well).
Add a 12 x 12 piece of aluminum on top of the wood roof.
Bend soft aluminum over the roof and let the metal edges hang down 1/4" below the wood (ala Jack Finch boxes) to stop water from wicking into the box.
Tilt the box slightly forward facing the ground. (Be VERY careful when opening for monitoring so that contents do not spill out.) Or tilt it to one side so water rolls to the side instead of towards the entrance.
Long vents should not be wider than 3/8", and vent holes should be no more than 3/4" in diameter, and should be protected by a large roof overhang. Vents should be as close as possible to the roof.
To prevent water from entering side vents, Linda Violett offers the following advice:
On existing boxes, clear EXTERIOR silicone caulk can be squirted in the shape of an eyebrow over the exterior of vents to divert water runoff and another squirt of caulk from the interior side of the box at the bottom of the vents (acts as a dam) for extra protection.
For slotted vents, a slat of wood (eave) can be positioned over the top portion of the slot vent to keep water from blowing/dripping into the boxes.
For new boxes, vents should be drilled from the outside of the box at an upward angle to prevent water from entering.
The Law: Technically, removing wet nesting material from an occupied nest site and replacing it with dry material or treating or replacing a nest infested with parasites may require a permit, depending on the specific circumstances. The Migratory Bird Treaty Act also prohibits possession of old bluebird nests without a permit. Consult the US Fish & Wildlife Service or your State wildlife management agency to be sure. More info.
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