Bluebird and Small Cavity Nester Conservation
Sialis - Bluebirds and other small cavity nesters
 
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Nests and eggs that may show up in bluebird nestboxes

ChickadeeHouse Wrenbluebird grass nestTree SwallowTufted TitmouseHouse Sparrow
Cavity nester photos of nests eggs and young

Cavity Nester Nests, Eggs and Young Photos and Bios. Also see Nest ID Matrix (contents) and Egg ID Matrix (color, spots, etc.)

Descriptions (click to jump to): Ash-throated Flycatcher | Bewick's Wren | Eastern Bluebird | Mountain Bluebird | Western Bluebird | Black-capped Chickadee | Carolina Chickadee | Carolina Wren | Cowbird | Eurasian Tree Sparrow | Great Crested Flycatcher | House Finch, House Sparrow | House Wren | Juniper Titmouse | mice | Mountain Chickadee | Nuthatches: (Brown-headed | Pygmy | Red-breasted | White-breasted) | Oak Titmouse | Prothonotary Warbler | Purple Martin | (European) Starling | Tree Swallowv Tufted Titmouse | Violet-green Swallow | Woodpeckers. Also see chart to help ID nests by construction material.

Eggs of various cavity nesters. Photo by Bet Zimmerman.One of the easiest ways to identify a nest is by the eggs. You can also gain clues by the shape of the nest and materials. There are several guides to nests and eggs. To identify eggs, it is helpful to know where they were found, color, markings, gloss, size, and shape.

Be aware there is often considerable variation in a nest of a particular species, depending on the individual, circumstances, location and available materials. Timetables vary. You may be able to identify the nester by watching what birds go in and out of the box with nesting material. But other birds may sit on or check out a box - with my birdcam, over a two day period I saw a bluebird, Starling, House Wren and Titmouse all sitting on or checking out a box claimed by a Black-capped Chickadee.

Other birds will enter a box being used by another species: e.g., House Sparrows and House Wrens for the purposes of attack; or other birds like bluebirds or Tree Swallows out of curiosity. If you see a parent feeding nestlings, you can be pretty sure. (There have been a few documented cases of birds feeding nestlings of other species though!) Usually Bluebirds, House Sparrows, House Wrens, and Tree Swallows are very visible (sitting on top of box, etc.) You may never see Chickadees or Titmice until the nestlings hatch and require constant feeding.

Other birds may also take over a nest started by another species, or two species may be trying to claim a box and build in it or lay eggs in it at the same time. Unless nests are removed after each fledging or at the end of the season (a good practice), material from a previous nesting by another species can confuse identification, which is why its best to go by eggs and adults.

NOTE:  You should welcome ANY native cavity nesters in your nestboxes. You may be able to change the birds you attract by moving boxes to different habitat, or by using different nestbox styles or sizes. See top tips for attracting bluebirds. It is illegal to disturb an active nest of any bird without a permit, except for House Sparrows, starlings and pigeons, which are not protected. Empty House Wren nests (sticks only, no nest cup or eggs) can be removed. More info.

Species are listed below alphabetically by Common name genus (e.g., Bluebird, Eastern; Bluebird, Western, etc.) along with links to "All About" pages on their nesting biology, and photos of nests, eggs and young.
SPECIES
NEST ID
EGG ID
Bluebird, Eastern
EABL
Bio | Photos
BBS Map
Neat, cup shaped, woven nest typically 100% fine grass or pine needles. Cup may be in the back of the box. Occasionally bits of fur or a few feathers, or even some hair (e.g., from a horse). Fairly deep, often cylindrical nest cup - usually 3-4" deep, with the cup portion 2.5" in diameter and about 2.25" deep. Eggs are powder blue (no dark spots), sometimes white. Surface is smooth, shape is subelliptical to short subelliptical.
Bluebird, Mountain
MOBL
Bio | Photos
BBS Map
Nest of dry grass, weed stems, pine needles, twigs, straw, rootlets, shreds of dry bark, and, sometimes, wool, hair (e.g., deer or horse), or feathers. Deep, well-formed cup lined with finer materials, and occasionally a few feathers or trash (shredded paper, plastic wrappers) Eggs are oval, smooth, glossy, unmarked, and are pale/light blue, bluish-white, or, rarely, white.
Bluebird, Western
WEBL
Bio | Photos
BBS Map
Collection of dry grasses/hay/straw, weed stems, and, sometimes, hair and feathers. Routinely add ribbons, strips of cellophane, thin bark (e.g., cottonwood fibers and cedar bark) and leaves to their nest, which may cause some to confuse it with a House Sparrow nest. Also conifer needles, moss, mammal fur/horse hair, dry rootlets. May be lined with finer grasses, nest not tightly woven. Linda Violett has also found straw wrappers (common), 8-track tape, shoestring, a large pink costume feather, flowers (Bougainvillea is "in" in 2007), plastic newspaper ties, polyester batting, leaves, cigarette filters, and plastic rings in WEBL nests.

Eggs are pale blue, bluish-white, or white.

 

Chickadee, Black-capped
BCCH
Bio | Photos
BBS Map

Downy nest with moss base, topped with a thick lining of fur and soft plant fibers. Distinct, small, deep cup. Female may cover eggs with a moss/fur "plug" when leaving the box.  Very thin-shelled white/cream eggs with light brown/reddish speckles, dots or blotches, little or no gloss, spots may be concentrated more on the wide end of the egg.
Chickadee, Boreal
BOCH
Chickadee Bio | Photos
BBS Map
   
Chickadee, Carolina
CACH
Bio | Photos
BBS Map
Nest base of moss, sometimes with strips of bark, thickly lined with grass, plant fibers, fur, hair (e.g., rabbit deer, squirrel, opossum, raccoon, cow, cat). Distinct, small, deep cup. Eggs are ovate to rounded ovate, white, finely marked with reddish-brown dots, spots or blotches, often concentrated on the larger end, little or no gloss.
Chickadee, Chestnut Backed
CBCH
Chickadee Bio | Photos
BBS Map
   
Chickadee, Mountain
MOCH
Bio | Photos
BBS Map
Nest of soft materials, with base of rotten wood chips or lichen, moss or grass, topped with loose fur or hair from mammal scat, owl pellets or other sources, (feathers?). Distinct (small and deep) cup molded in fur, then plugged with a blanket of looser fur used to cover eggs when not being incubated. Eggs are ovate, smooth shell with little or no gloss, pure dead white to entirely marked with reddish brown dots which may be concentrated on the larger end. Less heavily marked than Black-capped Chickadee eggs.
Cowbird, Brown-headed
BHCO
Bio | Photos |
BBS Map
Cowbirds do not build their own nest - they lay eggs in the nests of other birds, depending on the host to incubate and raise their young. Eggs are oval with variable shape, with a moderately glossy, granulated shell, white or grayish white, evenly dotted with brown/ reddish brown/gray, sometimes with heavier markings at the large end. Granulated, moderately glossy. Similar to a House Sparrow egg, but larger (size varies). The eggs of the Bronzed cowbird are pale bluish-green and have no markings.
Eurasian Tree Sparrow
ETSP
Bio | Photos

Domed structure of loosely intertwined (not woven) stems of dried grass, straw, pine needles and rootlets, a few sticks, surrounding a cup lined with softer materials such as feathers, fur, flower parts, waste paper, bits of cloth, string, and green leaves. Entrance is on side. May fill box to top. Currently only found in MO and IL.

NON-NATIVE. DO NOT ALLOW IN NESTBOXES UNLESS PROTECTED IN YOUR STATE

4-7 eggs, 0.8" eggs are white to pale gray, heavily marked with dark brown (sometimes purplish or grayish) spots/small blotches/speckles, darker than a House Sparrow. Markings usually concentrated around broad end. Smooth, slightly glossy. Great variation in size, shape, and color.
Flicker
Use wood shavings provided.  
Flycatcher, Ash-Throated
ATFL
Bio | Photos
BBS Map
Messy, typically with rootlets, grass, weed stems, and dry cow or horse dung in the nests, and a cup lined with fine grass and matted hair/fur. Unlike Great Crested Flycatchers, they seldom add snakeskin to their nests. Eggs are oval, smooth, slightly glossy,creamy white to ivory, and sometimes pinkish white background color, heavily marked with fine or heavy streaks or blotches in browns, purples, and grays (fewer markings than GCFL eggs.)
Flycatcher, Great Crested
GCFL
Bio | Photos
BBS Map
Bulky nest constructed of twigs, leaf litter, pine needles, bark, moss, lichen, grass, and rootlets, usually about 10-18" high (most are 12-15"). Off to one side a cup is lined with finer hair, feathers or fur. A piece of snakeskin or cellophane is often found in the nest. Eggs (larger than a HOSP egg), moderately glossy, ivory/cream/pink, and densely streaked/scrawled with fine purple, gray, red, brown, or olive markings often concentrated on the larger end of the egg.
House Finch
HOFI
Bio | Photos
Primarily of twigs, grasses and debris. May contain slender, dry stems with small leaves attached, lined with soft, wooly branch tips. May contain grass stems, plant fibers, leaves, rootlets, hairs, string and wool, lichens. Sometimes nest in wreaths on doors of houses. Not typically found in nestboxes. After day 5, a halo of fecal material starts to forms on edges of nest, creating a filthy mess. Typically oval, smooth shell, slight gloss, pale bluish white/green with sparing, delicate black (or dark brown or olive) spots/dots, speckles or streaks on the large end of the egg, forming a fine, loose ring. Occasionally eggs are unmarked. Length may vary.

House Sparrow
HOSP
Bio | photos and more photos.
BBS Map

Loose jumble of odds and ends, including coarse grass (with seed heads), cloth, feathers, twigs and sometimes litter (e.g., clear plastic, cigarette filters). Mid-summer nests sometimes contain bits of green vegetation (mustards or mints.) Tall nest, often with tunnel like entrance, particularly when built outside of a nestbox. In a nestbox may have more of a cup shape, and may be built up to cover sides of box.

NON-NATIVE to U.S.. Do not allow to nest in nestboxes.

 

Eggs are cream, white, gray or greenish tint, with irregular fine brown speckles, shell is smooth with slight gloss. Variable background color, color and thickness of spots, and size

NOTE: House Sparrows are non-native invasive pests, and are not protected by U.S. law. They will attack and kill adult bluebirds (sometimes trapping them in the nestbox), and destroy eggs and young.  House Sparrow nests, eggs, young, and adults may be legally removed or destroyed. It is better to have no box at all than to allow House Sparrows to reproduce in one.

Nuthatch, Brown-Headed
BHNU
Nuthatch Bio | Photos
BBS Map
Nests may start with dried leaves, or be lined with pine seed husks, inner bark strips, wood chips, grasses, cotton and feathers. Eggs smooth (almost no gloss) with evenly distributed fine reddish-brown dots/small spots/blotches.
Nuthatch, Pygmy
PYNU
Nuthatch Bio | Photos
BBS Map
Nest cup of bark shreds, fine moss, grass, plant down, fur, hair, cocoons and other soft fibrous materials, most incorporate feathers. May also contain snakeskin and bits of cloth (wool or cotton) and papery material from wasp nests, string, grass blades. Never include conifer seed wings (see Brown-headed Nuthatch). May also "caulk" nest site cracks with hair and feathers. Eggs are short subelliptical to short-oval, little or no gloss, white, unevenly and sparingly speckled or finely spotted with chestnut-red, reddish/purplish brown, with heavier markings often at the large end.
Nuthatch, Red-breasted
RBNU
Nuthatch Bio | Photos
Nest of bark shreds, grass, moss and feathers. Eggs white, heavily or sparingly spotted and dotted with reddish brown, little or no gloss.May dab globs of pitch around hole. Eggs similar to White-breasted Nuthatch but smaller.
Nuthatch, White-breasted
WBNU
Bio | Photos
BBS Map
Nest base may be about 1/2" of bark (flakes and strips) and pellets of dried earth or lumps of mud. Matted nest of bark shreds, small twigs, grasses, rootlets, with fur, hair, feathers, cellophane, cigarette butts. Cup may be saucer shaped. Shell smooth, very little gloss, white (can be creamy or pinkish-white), usually heavily marked with light cinnamon brown/red/ lavender/gray speckles and spots, often denser at larger end. Subelliptical to short subelliptical.
Phoebe, Eastern
Photos
Not a true cavity nester (nests on ledges)  
Purple Martin
PUMA
Bio | Photos
BBS Map
Nest of grasses, twigs, bark, paper, leaves, string; nest cup lined with fine grasses, decorated with fresh green leaves. Eggs slightly glossy, pure white, larger than Tree Swallow eggs.
Prothonotary Warbler
PROW
Bio | Photos
BBS Map
Mainly mosses and liverwort, plus lichen, rootlets, small twigs and dry leaves, and strips of bark (e.g., grape and cypress), plant down. Usually neatly rounded, cup shaped hollow, smoothly lined with fine grasses and sedges, poison ivy tendrils, leaf stems and skeletonized leaves, fishing line, and feathers. Boldly and liberally spotted/blotched with dull reddish brown and pale purplish gray spots and splotches over the entire egg.
Starling, European
EUST
Bio | Photos

Nest is bulky and slovenly. The cavity is filled up with grass, weed stems, twigs, corn husks, dried leaves, pine needles, etc, with a depression near the back. Feathers, rootlets, paper, plastics, cloth, string etc. may also be added. The cup lining may include feathers, fine bark, leaves, fine grass etc. Some nests also have fresh green plants (thought to work as fumigants against parasites and pathogens) like yarrow in them. May occupy boxes with holes larger than 1.5 inches.

NON-NATIVE. Do not allow to nest in nestboxes.

The slightly glossy eggs are pale bluish- or greenish-white (rare reports of eggs with fine reddish-brown spots), and are slightly smaller and darker than a Robin's egg.

Swallow, Tree
TRES
Bio | Photos
BBS Map

Nest of grass or pine needles, usually lined with feathers. Feathers often placed to curl up over eggs. Flatter cup (about 2" diameter, up to 1.5" deep) than bluebirds. (Note: the start of a Tree Swallow nest can look like a House Sparrow nest - don't remove it unless you're sure!) Occasionally contain mosses, rootlets, aquatic vegetation, and other plant materials. Some trash possible: cloth, paper, plastic, tinsel, cellophane, rubber bands, birchbark, often white. Eggs are pure white (may appear pinkish when first laid up to 4 days) with a pointy end.
Swallow, Violet-Green
VGSW
Bio | Photos
BBS Map
Shallow, loosely constructed, sloppy nest made of straws, dry grasses, strips of bark rootlets, pine needles, lined with abundance of feathers (white preferred?). Occasionally fur or horsehair? Sometimes wood chips, plant down, fiberglass insulation, string, rope and paper. Cupped middle? Subelliptical to oval white eggs, no markings, smooth to non-glossy to slightly glossy. (Indistinguishable from Tree Swallow.)
Titmouse, Bridled
   
Titmouse, Juniper
JUTI
Titmouse Bio | Photos
BBS Map

Grass, moss, hair and/or feathers, shredded bark, sheep wool or 'cotton"; also straw, twigs, plant down, rope/string, oak blossom, snakeskin, sycamore seed balls, rootlets, leaves, wood chips. Usually lined with hair and feathers and other materials listed above. (More hair and shredded bark in base than Oak Titmouse.)

 

3-9 short subellipitcal to elliptical, white, may be faintly marked with tiny speckling of pale reddish brown, evenly scattered to scattered very sparingly, smooth and nonglossy or slightly glossy.
Titmouse, Oak
OATI
Titmouse Bio | Photos
BBS Map
A base of moss, next fine grass, then a thick topping of fur. The cup is deep and usually is filled with a wad of fur as a "blanket" to cover eggs while the hen is laying. Eggs are white, smooth and non-glossy or slightly glossy. Some have tiny pale reddish-brown speckles evenly and sparingly scattered over the egg.
Titmouse, Tufted
TUTI
Titmouse Bio | Photos
BBS Map
Downy nest of moss, fur, and soft plant fibers. Occasionally primarily crumpled up dried leaves with grass, and a bit of snakeskin, cellophane, bark strips, etc. Cup may be padded with hair, fur, bits of string, or cloth. May have earwigs living under moss.  Eggs are white with rose/mauve speckles, little or no gloss, more evenly distributed than chickadee.
Wren, Bewick's
BEWR
Bio | Photos
BBS Map
Bulky nest (sometimes domed) with a deep cup of grass, feathers, hair, plant down, moss and dead leaves on a base of short twigs/sticks, rootlets, chips/leaf debris, spider egg cases, oak catkins. May have a wider variety of material in the base, with finer materials in the cup. Often snakeskin or cellophane in cup, which is deep and tiny and may be in a back corner. May be a little more "organized" looking than a Carolina Wren nest. Do not fill up large cavities to the top like a House Wren. Eggs are oval or rounded oval, white with irregular brown, purple/gray spots/dots often concentrated in a ring on the larger end. Smooth with little or no gloss, unlike House Wren.
Wren, Carolina
CARW
Bio | Photos
BBS Map
Nest is a bulky, somewhat messy mass of debris like leaves with some coarse hay/grass, twigs, moss, little roots, weed stalks; strips of bark, plastic or even snakeskin; generally domed with tunnel like entrance; and lined with feathers, animal hair, Spanish moss, wool, and fine grasses. Eggs are white/pale pink or rosy tint/light gray (larger than other wren eggs); usually with heavy brown/reddish-brown flecks often concentrated at larger end. Little or no gloss, unlike House Wren.
Wren, House
HOWR
Bio | Photos
BBS Map
Messy nest of coarse twigs (often with cottony spider cocoons), lined with fine fibers and downy feathers, usually filling box. Males may build eggless "dummy nests" in nearby boxes to reduce competition.  Tiny glossy white eggs, often tinted pink/buff, with numerous pinkish brown/reddish brown/brown specks that generally form a ring on the larger end of the egg.
Woodpeckers
Downy Bio | Photos
Woodpeckers (Downy, Nuttall's) may enlarge the entrance hole and roost in bluebird nestboxes while roosting. Few woodpeckers nest in nestboxes, but if they do, they will use woodchips provided by the landlord.  
Mice
Info
Mice may breed or roost in a nestbox. Next constructed of a variety of materials, such as grass, leaves, hair, feathers, milkweed silk, shredded bark, moss, cotton, or shredded cloth. No nest cup. Rodent droppings are generally evident.  
Squirrels, Gray or Red
Info on Red Squirrels
Gray or red squirrels may occupy boxes with holes larger than 1.5 inches.  
Flying Squirrels
Info
Flying squirrels may also use boxes. Bulky, no cup, strippable bark (e.g., cedar, grape), grass, lichen/moss, fur, feathers, small twigs, tree leaves (deciduous and coniferous), and trash (insulation, newspaper). Acorns may be found in box. Natal nest is 700% larger than solitary male nest. More info.

IDENTIFICATION GUIDES
  • (Bird ID) The Sibley Guide to Birds, Sibley, David Allen
  • (Nest ID) A Field Guide to the Birds' Nests: United States east of the Mississippi River (Peterson Field Guide Series), Harrison, Hal H.
  • (Nest ID) A Field Guide to Western Birds' Nests, Harrison, Hal H.
  • (Nest ID) yJ. Colin James, O. Harrison
  • What Bird (adult bird ID - browse by location, shape, color, etc.)
  • Online guide to adult birds, where you enter location and whatever info you have (like color) and it shows you photos (unfortunately this site now seems to require a username and password.)

FOR MORE INFORMATION:

PHOTO CREDITS: Many thanks to the following people who allowed me to use their awesome photographs: Bluebars (from the Bluebirding Forum), Dick (BBnut) from PA (from the Bluebirding Forum), Pam from New Jersey, Susan Costa, Shelly Harris of Oklahoma. Steve Hewlett, Leslie McCulloch, Tracy Powell, Leah Solliday from Florida, and Photography of bluebirds and snowy owls. BZ is me - Bet Zimmerman from CT.

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Mouths are open. Eyes are closed. Hints of fuzz where feathers will grow are visible. How do such ungainly, scrawny little creatures ever acquire such phenomenal beauty?
- Shirl Brunnel, I Hear Bluebirds, 1984

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