*Oology is a branch of ornithology studying bird eggs, nests and breeding behaviour. The word is derived from the Greek oion, meaning egg.

17. Black-headed Grosbeak

This part of the Stanislaus Audubon Website is focused on 44 common Central Valley nesting species with background about their nesting habits. Please check the Great Valley Museum Central Valley Egg Collection starting page for links to all the featured species.

BLACK-HEADED GROSBEAK NESTING INFORMATION (From birdsoftheworld.org)

Nests - Pairs form soon after females return to breeding areas in spring. nest-building begins in late April or early May. Nest is typically placed in outer branches of a small deciduous tree or bush, often near a stream. Female does virtually all building. Nests widely reported to be so thinly constructed that eggs can be seen through bottom. Nest is an open cup, bulky and loosely constructed. No mud or other cementing agent is used. Outer bowl is constructed of slender twigs, plant stems, rootlets, and pine needles.
Eggs - Subelliptical or oval, Pale blue or greenish blue with brown or reddish brown spotting and/or blotching, usually more concentrated around larger end. Clutch size average is 3 (range 2-5).
Incubation - Both sexes sit on eggs. Eggs hatch 12–14 d after onset of incubation.
Fledging - Altricial, hatch with eyes closed, naked except for sparse grayish white down. Leave nest between 10 and 14 days.

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