Bluebirds – predation control

This is the third article in a series related to attracting bluebirds to your yard and properly caring for them.

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Predation Control

Properly mounting your nest boxes is an important part of caring for bluebirds.  Nest boxes should never be nailed to trees, fence posts, or outbuildings.  Climbing varmints including cats, raccoons, foxes, possums, and rat snakes can easily reach the nest box and harm the bluebirds.

The proper way to mount bluebird nest boxes is to attach them to metal poles equipped with approved predator guards under the nest box to deter climbing varmints.  Generally speaking, the bottoms of nest boxes should be about 5 feet above ground to facilitate monitoring activities.  Creating a 3-foot diameter circular barrier centered around the mounting pole filled with several inches of white play sand will help deter rat snakes as well as display paw prints and signs of  other unwanted visitors.  The sand must be kept clean and loose by raking it after every hard rain.

Placing a molded wood fiber nest cup in the nest box will enable you to inspect the nest without destroying its physical integrity.  Be sure the nest cup fits snugly in the bottom of the nest box.

Keep the grass around the base of the nest box trimmed and free of yard debris that could provide a hiding place for predators.

Check the area around the nest box for ant hills especially fire ants.  Dispose of ant hills immediately by spraying them with an organic pesticide such as Pyrethrin.  Cover up treated ant hills with dirt to prevent ant-eating birds such as Northern Flickers from ingesting the poisoned ants.

Spray the metal mounting pole with PAM cooking spray to deter ants and mites from climbing the pole.  You will need to re-apply the PAM from time to time.

Inspect your nest boxes frequently for active wasp infestations.  Bluebirds often will not select nest boxes with wasp infestations and may abandon nests that have become infested.  If you encounter an active wasp infestation, don padded garden gloves and physically destroy the wasps and their nest including the nest stem.
Do NOT spray the interior of nest boxes with pesticides of any kind.
Apply a generous coating of unscented ivory soap on the interior of the roof, sides, and door to deter subsequent wasp infestations.

Tip:  Always check the interior of the nest box door from the side first.  Wasps will often build their nests on the interior of nest box doors and you may be stung on the hand if not careful.

Check the nest box and interior of the nest for mites.  You will have to look very closely and may even need a magnifying class to see them.  If you find a mite infestation, use a molded wood fiber nest cup and make an artificial nest of pine straw or rough dried grasses lined with fine grasses.  Carefully remove the eggs or nestlings from the mite-infected nest, dust them off with a very fine soft brush and place them in the artificial nest.  Thoroughly clean the nest box with a cloth and warm water.  Bag and dispose of the infected nest.  Re-insert the artificial nest into the clean nest box.

Nest box mounting supplies and molded wood fiber nest cups can be purchased at most wild song bird supply stores.

Contact me bluebird-shepherd if you would like free D-I-Y plans for nest boxes and mounting systems.

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New Neighbors

This is the second article in a series related to attracting bluebirds to your yard and properly caring for them.

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New Neighbors 05-24-2007

May 25, 2007

  New bluebird neighbors moving into Gilbertson style nest box.

This morning a bluebird couple claimed a Gilbertson style bluebird nest box located about 20 feet across the driveway from our back door.  The process was filled with a number of small challenges that are often associated with bluebird nest site selection and nest building.

Challenge #1

The young female bluebird began to attack her reflection in our kitchen window.  I closed the curtains and that helped for a few minutes.  Then she started visiting our cars parked in the driveway and attacked her reflection in the windshield and side view mirrors.  I relocated both cars some distance from the driveway. She then joined her mate in sitting on top of the Gilbertson nest box.

Note:  Bluebirds become quite territorial during nesting season.

Challenge #2

Birds feeding on a feeder array near the Gilbertson distracted the bluebirds from building their nest.  I relocated the feeder array to another part of the yard some distance from the Gilbertson nest box.  The bluebirds settled down and started going in and out of the nest box.

Note: Feeders located too close to the nest box may disturb bluebirds and distract them from the nesting process.

Challenge #3

The young female bluebird apparently had never built a nest before and did not know how to begin.  She repeatedly went into and out of the nest.  She landed beside her mate on top of the nest box and they engaged in animated conservation.  The male flew into the yard and picked up a piece of pine straw in his beak and deposited it inside the nest box.  He then landed on the roof beside her and they had another conversation of sorts.  She flew into the nest box, stayed a couple of minutes, and then returned to the top of the nest box.  The male repeated the process of placing one piece of pine straw in the nest box.  This time the female must have understood because she flew into the yard and returned with a big wad of pine straw in her beak and entered the nest box with it.

Note:  Put several small handfuls of pine straw or clumps of dried grass in the general vicinity of the nest box to facilitate nest building.

Bluebird Nesting Basics

Bluebirds are secondary cavity nesters.  That is to say, they use available cavities or nest boxes in which to build nests and raise their young.  They do not excavate their own cavities as do some species of woodpeckers.

Nest Selection & Building

The male bluebird identifies and assesses potential nesting sites.  He then tries to persuade his mate that one of the nesting sites is ideal for their needs.  The male will often sit on top of a nest box and sing to attract the female’s attention to the box.  The male may even go so far as to leave a piece of pine straw protruding from the entrance hole to entice her to enter the nest box.

The female bluebird makes the final decision on which nesting site to use and she builds the nest in preparation for the egg-laying step. 

Note:  Nest selection & building can occur in 1 day or take several weeks to complete. 

Egg laying

The female lays one egg per day usually first thing in the morning until all the eggs in the clutch have been laid.  The typical clutch size for Eastern bluebirds is 3–5 eggs.  The range is between 2–7 eggs per clutch.  Clutch sizes larger than 7 eggs have been reported but are thought to be the result of additional eggs deposited by another female bluebird experiencing problems with her own nest.  The process of depositing eggs in other nests is referred to as “egg dumping.”

Note: The egg-laying step takes one day per egg until the entire clutch of eggs has been laid.  Five days will be required for a clutch size of 5 eggs. Bluebird eggs are oval shaped and blue in color.  In rare cases, bluebird eggs may be white in color and hatch normally.


The female bluebird incubates or regulates the temperature of the eggs as needed depending upon the ambient temperature.  She develops a “brood patch” on her stomach. The brood patch is an area where the down covering thins and blood vessels near the surface or the skin enlarge to allow her to better transfer body heat to the eggs. The incubation period is 11–19 days (13–14 days is typical) but can vary due to temperature and weather conditions.

Egg Hatching

Hatching is the next step in the nesting cycle.  The eggs hatch usually all on the same day in the order they were laid.   Just hatched baby bluebirds are referred to as “hatchlings.”

Nestling Stage

For the remainder of their time in the nest, baby bluebirds are referred to as “nestlings.”  During this stage, the nestlings develop and mature in preparation for leaving the nest.  The nestling stage has a range of 16–21 days. The typical nestling stage is 17–18 days in duration.

Fledgling Stage

One by one the nestlings leave the nest on their solo flights and become fledglings.  Once out of the nests, fledglings do not return to the nest on their own.  For the next two weeks after they have fledged, the new bluebirds are taught how to fend for themselves by their parents.

Extended Family

An extended family of bluebirds may be observed later in the the nesting season.  This happens when the offspring of earlier cycles remain with their parents throughout the remainder of the nesting season.  They can be seen accompanying the parents and even helping to feed the nestlings of a later cycle.  The extended family dissolves before the next nesting season as the bluebirds select their own mates and search for suitable nesting sites.

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Attracting bluebirds to your yard

Bluebird Breakfast 

Eastern Bluebirds dining on cracked sunflowers seeds

This the first in a series of articles to help readers attract bluebirds to their yards. If you would like to leave a comment, click on this comment link, enter your comment, and submit it.

If you have specific questions regarding bluebirds, click on the link immediately below.

Bluebird Question? 

Bluebird Factoid

Did you know there are three species of bluebirds?

Eastern             Sialia sialis

Mountain           Sialia currucoides    

Western            Sialia mexicana

Did you know two of the bluebird species have subspecies?

Subspecies of Eastern Bluebirds        

  1. Sialia sialis bermudensis (Verrill)
  2. Sialia sialis caribaea (Howell)
  3. Sialia sialis episcopus (Oberholser)
  4. Sialia sialis fulva (Brewster)
  5. Sialia sialis grata (Bangs)
  6. Sialia sialis guatemalae (Ridgway)
  7. Sialia sialis meridionalis (Dickey and van Rossem, considered part of guatemalae by Webster)
  8. Sialia sialis nidificans (Phillips)

Subspecies of Western Bluebirds

  1. Sialia mexicana amabilis (Townsend)
  2. Sialia mexicana anabelae (Anthony, not on Phillips list)
  3. Sialia mexicana bairdi (Ridgway)
  4. Sialia mexicana jacoti (Phillips)
  5. Sialia mexicana mexicana (Swainson)
  6. Sialia mexicana nelsoni (Phillips)
  7. Sialia mexicana occidentalis (Townsend)

There are currently no recognized subspecies of Mountain Bluebirds.

* Source for subspecies information : Sialis


The following is a brief description of the five basic steps needed to attract bluebirds to your yard and properly care for them.

#1 Nest boxes

Put up safe, comfortable, and durable bluebird nest boxes in suitable spots around the yard. Bluebirds generally prefer open grassy areas near a suitable vantage point (power line, tree, gutter, roof top, etc.) on which they can perch. Avoid placing nest boxes in tree cover or near large bushes, shrubs, and thickets because these spots attract house wrens. Although not a hard rule, try to orient the entrance of nest boxes facing in a southeasterly direction. Ensure nest boxes have adequate ventilation. Be sure to mount the nest boxes on metal poles equipped with a predator guard/baffle. The predator guards will deter climbing varmints such as raccoons and rat snakes from invading the nest boxes and harming the bluebirds. If the nest boxes are in direct line of sight of one another be sure to allow a minimum of 100 yards between them. Keep the ground around the poles weeded and check frequently for ant hills especially fire ant hills. You can spray the mounting poles with PAM cooking spray to deter ants. Destroy all ant hills in the immediate vicinity of your nest boxes. Either physically destroy the nests by digging them up or spray them with an organic pesticide such as Pyrethrin which is available at hardware stores. If you use the spray, immediately cover up the ant hills with dirt to prevent ant-eating birds from ingesting the poisoned ants. You can view plans for safe, comfortable, and durable nest boxes at help-for-bluebirds (click on nest box plans). You can buy acceptable bluebird nest boxes from your local N. C. State Employees’ Credit Union branch for $10 each. You do not have to be a member to buy nest boxes but you will have to pay cash if you are not a member. You can buy mounting poles, brackets, and predator guard/baffles from hardware stores, Lowes, Home Depot, Wal-Mart, etc. Ace Hardware sells an excellent 18″ diameter cone-shaped predator guard/baffle for about $20. Buy some bars of unscented ivory soap and rub a good coat of soap on the interior of each nest box (roof, sides, and door). This will help deter paper wasp infestations which discourage and often prevent bluebirds from nesting in the box. If you find a wasp nest in a box, immediately destroy the wasps, remove, and destroy the wasp nest including the stem. Do not spray the interior of nest boxes with pesticides. Be sure to check under nest boxes and predator guards/baffles for wasp nests. When you open nest boxes to check for wasps, stand to the side of the doors, open them slowly, and be sure there are no wasp nests attached to the inside of the doors. Otherwise you may be stung on the hand. Wear padded garden gloves when you check the boxes. Use molded wood fiber nest cups in all of your wood nest boxes. The cups will facilitate nest building for the birds and monitoring activities for you. Cleaning the nest box will also be easier if you use a nest cup. Always clean nest boxes thoroughly and dispose of old nests after each nesting cycle during the nesting season. You can buy molded wood fiber nest cups at wild song bird supply stores.

#2 Feeding Stations

Establish several feeding stations around the yard. Bluebirds and other wild songs will feed at the stations. Bluebirds will be attracted to feeders containing cracked sunflower seeds, suet, peanut suet nuggets, and meal worms especially when they are feeding nestlings or their normal diet (~68%) of insects is hard to find. You probably want to use squirrel proof feeders that can be adjusted to close when a certain amount of weight is sensed. You can buy the seed supplies at Wal-Mart, Lowes, Home Depot, and other stores that sell supplies for wild song birds. Mealworms can be purchased via the Internet or at wild song bird supply stores like Wild Birds Unlimited. There are also a number of recipes for making your own suet to feed bluebirds. Use the Google search engine to search for bluebird suet recipes.

You can make your own wild bird seed mix using:

– sunflower seed combo (black oil & striped)

– safflower seeds

– cracked sunflower seeds

– peanuts

– Nut n’ Berry mix

Be sure to feed suet year round. In the heat of summer, switch to the non-melt type of suet cakes. Be sure to keep the area around your feeders free of weeds that could hide cats and other lurking predators. Remove discarded seed from the ground around the feeders that might mold and sicken the birds who eat it.

#3 Fresh Water

Provide shallow bird baths containing fresh water near the feeding stations. Change the water daily and keep the bird baths clean and free of mold. Avoid deep bird baths because very young birds are not quite ready to fend for themselves and may drown if their parents are not around to save them. You can buy an acceptable bird bath from Wal-Mart for about $10. Be sure to keep the area under bird baths clear of weeds that can hide lurking cats and other predators.

#4 Plant berry-bearing trees and shrubs

There are a number of berry-bearing trees and shrubs that bluebirds favor as food sources. You can contact your local County Extension Agent or Garden Club for recommendations.

#5 Join the N. C. Bluebird Society and become an active bluebirder

You will be able to share experiences with expert bluebirders at Annual Meetings. You will also be eligible to contribute to this BLOG. Annual memberships cost $10 and they make great gifts for friends and relatives. Membership information and forms are available from the N. C. Bluebird Society web site.

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