Bluebird Nesting—Possible Occupants


Nesting Activities
Tree Swallows
House Wrens
House Sparrows
Earliest arrival First week in March Last week in March Late April Permanent Resident
Peak arrival Mid to late March Mid to late April Early May Permanent Resident
Breeding season Mid to late April Mid May Late May Late April to early May
Peak departure Late Sept. to early Nov. July and Aug. Early Sept. Permanent Resident
Nest Building
Location of nest (in natural cavities) Open country with scattered trees to wood borders, near mowed or sparsely covered ground Partly open country with old or dead trees, often near water Partly open country with old or dead trees, often near water Open woodland and wood borders, shrubland, farmland, suburbs, up to 200′ from cover  Hole or crevice anywhere, especially by buildings
Male claims nest with: Grass (1-6 weeks before nest building) Curved white feathers Twigs with spider egg cases Grass or sitting in hole
Materials Dry grass and weed stems, pine needles (occasionally fine rootlets or twigs), lined with finer grass (occas, hair or feathers) Dry grasses (occasionally straw, cattails or pine needles), lined with feathers (often white) Twigs with spider egg cases (occasionally stems, leaves, fibers), lined with fine grass, feathers, hair, bark strips Long coarse grass stems with seed heads, weeds, feathers, trash
Size and Shape Loosely built with 2-3″ cup Loosely woven with large, shallow cup, feathers uprights curving over eggs Bulky base of twigs (nearly filling box) with small deep cup at top rear Large untidy dome with side entrance to deep space with little or no bottom
Days to build and builder 4-11 days usually (2-14 days possible) by female usually; can be up to 1 week before 1st egg is laid 14-21 days usually (7-30 days possible) by female 8-10 days for male to build base; 4 days for female to line; can be up to 2 days before 1st egg is laid Can be built in 1 day, usually by male
Color/Size Blue to white, somewhat glossy White, slightly glossy to non-glossy Light pink to white with rust specks Off-white to bluish-green with gray/brown spots
Total number laid 4-6 eggs (3-7 possible) 5-6 eggs (4-8 possible) 5-8 eggs (up to 12 possible) 4-6 eggs (3-8 possible)
Incubation period 12-14 days (12-18 possible) 14-15 days (13-16 possible) 13 days (12-15 possible) 12 days (10-14 possible)
Hatch timing Approximately same time Approximately same time Approximately same time Approximately same time

Do Not Disturb

(age when nestlings could prematurely fledge)

12 days 15 days 9 days Remove eggs before they hatch
Total time in nest 17-18 days (15-20 possible) 20-21 days (16-24 days possible) 16-17 days (12-18 possible) 15-16 days (14-17 possible)
Number of broods 2 broods sometimes 3 1 brood (rarely 2) 1-2 broods (rarely 3) 2-3 broods (sometimes 4)