Independent birding guide — not affiliated with the original Bird-a-Day challenge or the domain's previous owner.
Birdaday Field Notes

Species profile

Eastern Bluebird: identification, look-alikes, nest boxes and bluebird trails

The Eastern Bluebird is the small thrush that perches upright on wires and fence posts over open grass, then drops to the ground for an insect (Cornell). It is also the bird behind the nest-box movement: bluebird trails and box campaigns in the 1960s and 1970s helped it recover after introduced House Sparrows and European Starlings took over its nest holes (Cornell).

Quick facts

Fact Eastern Bluebird
Scientific name Sialia sialis, family Turdidae, the thrushes (Cornell)
Length 6.3–8.3 in, 16–21 cm (Cornell); 6–8 in (Audubon)
Weight 1.0–1.1 oz, 28–32 g (Cornell); 28–31 g (Audubon)
Population Global breeding population of about 23 million (Partners in Flight, via Cornell; Audubon lists the same figure)
Trend Increased from 1966 to 2019 (North American Breeding Bird Survey, via Cornell)
Status Low Concern, Continental Concern Score 7 of 20 (Cornell); Least Concern (IUCN, via Audubon)
Oldest known At least 10 years 6 months, banded in New York in 1989 (Cornell)

How to identify an Eastern Bluebird

Cornell describes a small thrush with a large, rounded head, a large eye, a plump body, long wings, a fairly short tail and a short, straight bill, about two-thirds the size of an American Robin.

Eastern Bluebird perched on a bare twig with one wing raised: deep blue head, back, wings and tail, rusty-orange throat and breast, white lower belly Female Eastern Bluebird perched on a weathered wooden post: gray head and back, orange-brown breast, pale belly, blue edges on the wings and tail
Left: Eastern Bluebird in Frederick County, Maryland (February 2026), a Quality image on Wikimedia Commons, showing the deep blue upperparts and rusty throat and breast that Cornell describes for the adult male. Right: female Eastern Bluebird, as identified on the Commons file page (January 2013): grayish above, orange-brown breast, blue in the wings and tail (Cornell).
Photos: Acroterion / CC BY-SA 4.0, via Wikimedia Commons; Dakota L. / CC BY-SA 3.0, via Wikimedia Commons

Eastern vs Western vs Mountain Bluebird and Indigo Bunting

Cornell lists these three as similar species. The table compares field marks from Cornell's identification page for each.

Field mark Eastern Bluebird Western Bluebird Mountain Bluebird Indigo Bunting
Length 6.3–8.3 in 6.3–7.5 in 6.3–7.9 in 4.7–5.1 in
Male throat Rusty, wrapping up the sides of the neck Blue Sky-blue (no rust) Blue
Male breast Rusty or brick-red Rust-orange vest that extends onto the upper back Paler sky-blue, white under the tail Blue all over (breeding)
Female Grayish above, orange-brown breast Gray-buff, pale orange wash on breast, gray-buff throat Mostly gray-brown, sometimes an orange-brown wash on the chest Mostly brown, faint breast streaks, whitish throat
Habits Open country in the East Open parklands of the West Often hovers while foraging; western mountains and plains Brushy edges; swishes its tail

On a male: a blue throat means Western, no rust means Mountain, and a small, all-blue bird in a hedgerow is an Indigo Bunting.

Song and calls

If your Bird-a-Day house rules count heard birds, the call is enough to log the day.

Food and feeders

Topic What the sources say
Main food Insects caught on the ground for much of the year: caterpillars, beetles, crickets, grasshoppers and spiders (Cornell). Audubon adds earthworms and snails
Fall and winter Lots of fruit, such as sumac, dogwood, hackberry and juniper berries (Cornell)
Feeders Rarely come to feeders unless mealworms are offered (Cornell)
Mealworms NABS: live mealworms only for nestlings ("never" freeze-dried); about 100 a day for a pair feeding young, split morning and afternoon; mealworms are low in calcium, so dust them with calcium powder or offer them only as a supplement

NABS warns that mealworms will not attract bluebirds if none live nearby. More on feeder styles: bird feeder types compared.

Nesting

The male shows a female the cavity; only the female builds the nest, a loose cup of grasses and pine needles lined with fine grass, and incubates (Cornell). Natural sites are usually old woodpecker holes in dead pine or oak, up to 50 feet up (Cornell); Audubon gives usually 2–20 feet.

Stage Cornell Lab Audubon North American Bluebird Society (NABS)
Clutch 2–7 eggs 4–5, sometimes 3–7 Typically 4–5, sometimes 6–7
Incubation 11–19 days About 13–16 days, mostly by the female Usually 12–14 days
Nestling period 17–21 days Leave at about 18–19 days on average 17–21 days
Broods 1–3 2, sometimes 3 Most raise 2; 3 or 4 in warmer climates
Start of nesting — — Usually late March or early April; as early as late February in southern states
Eastern Bluebird nesting timeline and when to stop opening the box A horizontal timeline in days from the first egg. 1 Egg laying, one egg a day, about 5 days for a typical clutch. 2 Incubation, usually 12 to 14 days, hatching about 17 to 18 days after the first egg. 3 Nestlings in the box, 17 to 21 days. 4 From nestling day 12 or 13, look only from a distance; do not open the box. 5 Fledging. 1 2 3 4 5 05183039 days after the first egg (example: 5 eggs, hatch day 18, fledge at 21 days) Laying Incubation 12–14 d Nestlings 17–21 d open to check look, don't open
  1. Laying: most cavity nesters lay one egg a day (NABS); a typical clutch is 4–5 eggs.
  2. Incubation: usually 12–14 days; eggs typically hatch about 17–18 days after the first egg was laid (NABS).
  3. Nestlings: usually in the box 17–21 days (NABS, Cornell).
  4. From nestling day 12–13: open the box only with caution, if at all, or view it from a distance, because the young may leave before they can fly (NABS).
  5. Fledging: remove the old nest once all young have left; this may encourage another brood (NABS).
Drawn for Birdaday Field Notes from the North American Bluebird Society's Getting Started and Monitoring fact sheets, cited below. The day axis is one worked example using typical values; real nests vary. Drawn to scale for that example only.

Nest box specifications

NestWatch (the Cornell Lab's nest-monitoring project) and the North American Bluebird Society give different numbers, so both are shown.

Spec NestWatch (Eastern Bluebird page) NABS Nestbox Recommendations (2018)
Entrance 2¼ in 1½ in round, 1⅜ × 2¼ in vertical oval, or 1⅛ in horizontal slot; 1 9⁄16 in where Western or Mountain Bluebirds also occur
Floor 5½ × 5½ in 4 × 4 in up to 5½ × 5½ in
Depth 9 in inside 4½–6 in from entrance hole to floor
Height 4–6 ft above ground Entrance at least 5 ft above ground
Facing East, toward open habitat East or south, away from prevailing winds
Mount Pole Smooth pole such as metal conduit; not tree trunks

NestWatch's 2¼-inch figure equals the long side of the NABS oval and is larger than any round hole NABS recommends, so check the plan you build from. In one study cited by Cornell, bluebirds preferred 1.75-inch holes to 1.4-inch ones and 4-inch floors to 6-inch. Our birdhouse dimensions table compares other species.

Cutaway of a bluebird nest box on a guarded pole Side cutaway of a wooden nest box on a metal pole. 1 Entrance hole high on the front. 2 Distance from the bottom of the hole to the floor. 3 Floor. 4 Sloped roof overhanging the front. 5 Vent holes high on the side under the roof. 6 Drainage at the floor corners. 7 No perch; rough or grooved inside wall under the hole. 8 Entrance height above ground. 9 Predator guard on the pole below the box. 1 2 3 4 5 6 7 8 9
  1. Entrance: 1½ in round, 1⅜ × 2¼ in vertical oval or 1⅛ in horizontal slot for Eastern Bluebirds (NABS); NestWatch's page lists 2¼ in.
  2. Hole to floor: 4½–6 in (NABS). NestWatch lists 9 in of inside depth.
  3. Floor: 4 × 4 to 5½ × 5½ in (NABS); 5½ × 5½ in (NestWatch).
  4. Roof: overhang at least 2 in, 3–5 in preferred, especially at the front (NABS).
  5. Vents: high on the sides under the eaves, for example three ⅜-in holes per side (NABS).
  6. Drainage: cut-off ("dog-eared") floor corners or ¼–½ in holes (NABS).
  7. No perch: keep the inside wall under the hole rough or cut with grooves so young can climb out (NABS).
  8. Height: entrance at least 5 ft above ground (NABS); 4–6 ft (NestWatch).
  9. Predator guard: a wobbling stovepipe, PVC baffle, hardware cloth or Noel guard on a smooth pole (NABS).
Drawn for Birdaday Field Notes as a generic box, following the NABS Nestbox Recommendations and Getting Started fact sheets and NestWatch's Eastern Bluebird page, cited below. Not to scale.

Running a bluebird trail

A bluebird trail is a series of boxes checked through the season. Steps from NABS, NestWatch and the Tennessee Wildlife Resources Agency (TWRA):

  1. Pick open ground with scattered trees, such as pastures, parks and golf courses, without heavy pesticide use, 50–200 feet from brushy House Wren habitat and away from barns, feedlots and cheap millet seed that draw House Sparrows (NABS).
  2. Space the boxes. At least 100 yards apart for Eastern Bluebirds, 125–150 yards may be better (NABS); TWRA says at least 100 yards; NestWatch gives 300 feet.
  3. Pair boxes where Tree Swallows are common. The distance within a pair differs by source: 5–15 feet (NABS), 15–20 feet with pairs about 300 feet apart (NestWatch), within 25 feet (TWRA).
  4. Guard every pole; wooden guards do not stop raccoons (NABS).
  5. Have boxes up by early spring, and leave them up where bluebirds stay all year; they roost in them on cold nights (NABS).
  6. Check at least once a week in calm, mild, dry weather and record eggs and young (NABS). NestWatch suggests every 3–4 days, visits under 1 minute, late morning or afternoon, and a tap on the box before opening.
  7. Stop opening at nestling day 12–13 (NABS). If you must look later, Sialis.org suggests an inspection mirror and flashlight, or opening the box only a crack.
  8. Clean out the nest after each brood fledges (NABS). TWRA suggests moving a box with no native nesters after two years.

House Sparrows and the law

NABS says House Sparrows kill adult and nestling bluebirds and destroy eggs, and are non-native and "not protected under federal law"; state and local laws vary. Interfering with an active native nest without a permit is illegal under the Migratory Bird Treaty Act (NABS). So identify first: a bluebird nest is a neat cup of fine grass or pine needles with 4–6 powder-blue eggs; a House Sparrow nest is a tall, messy pile of coarse grass, feathers and trash with 5–7 cream or greenish, brown-marked eggs (NABS).

For your Bird-a-Day streak

Bluebirds are permanent residents in many southern areas (Audubon), so a known pair near a box is a dependable "reserve bird." Plan the rest with the species planner.

Eastern Bluebird checklist

Sources