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Acorn
Woodpecker
Melanerpes formicivorus Swainson
Field
Guide IDs:
NG-274; G-198; PW-pl 40; AW-pl 376;
AM(II)-222
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BREEDING:
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Oak and mixed
oak/conif woodland, often in foothills. Requires
acorns and storage trees. 1, rarely 2
broods.
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DISPLAYS:
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Bowing and wing
spreading commonly seen; some aerial
displays.
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NEST:
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Usu decid snag, esp
oak, also poles. Lined with chips.
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EGGS:
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White. 1.0" (25
mm).
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DIET:
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Mostly insects;
also acorns, fruit, sap, corn. In fall/winter
groups hoard by studding "storage" trees, utility
poles, other wooden structures with up to 50,000
acorns. Also hoard almonds/walnuts/
pecans.
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CONSERVATION:
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Winter
resident.
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NOTES:
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Live in communal
groups of up to 16, consisting of at least 2
breeding adults plus their young of previous
nestings and cousins. Large clutches result of 2
females. Reproduction highly dependent on size of
acorn crop. In CA maintain all-year communal
territories, with communal acorn stores. In AZ,
some nest as lone pairs and migrate if insufficient
food is stored; some AZ populations do not hoard.
Young independent at ca. 2 months. Often evicted
from nest cavity by starlings. Attack squirrels,
jays, nuthatches, titmice, and esp Lewis'
Woodpecker (which also store acorns) that raid
caches.
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STANFORD. NOTES:
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Common resident
virtually wherever there are mature oaks. Social
groups establish territories in which they collect
acorns and cache them in the limbs and trunks of
oaks, palms, eucalyptus, and occasionally the eaves
of buildings. These caches are defended against
Western Scrub-Jays and other groups of Acorn
Woodpeckers. Although populations have declined in
surrounding urban areas, those on campus should
persist if mature oaks remain available.
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ESSAYS:
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Cooperative
Breeding;
Hoarding
Food;
ParentalCare;
Monogamy;
Island
Biogeography;
Interspecific Territoriality
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REFERENCES:
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Koenig and Mumme,
1987; Stacey and Bock, 1978.
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