Acorn Woodpecker

Melanerpes formicivorus
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STANFORD LOCATIONS:

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. 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.
  
Nest
Location
Nest
Type
Eggs
Mating System
Dev.
Parental Care
Primary &
2ndary Diet
Foraging
Strategy
MF
I: 11-12 DAYS
ALTRICIAL
20 feet - 25 feet
(6 feet - 60 feet)
MF+
3-7
(7+)
COOP
F: 30-32 DAYS
MF+
BARK DRILL
HAWKS
BREEDING: Oak and mixed oak/conif woodland, often in foothills. Requires acorns and storage trees. 1, rarely 2 broods.
DISPLAYS: Bowing and wing spreading commonly seen; some aerial displays.
NEST: Usu decid snag, esp oak, also poles. Lined with chips.
EGGS: White. 1.0" (25 mm).
DIET: 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.
CONSERVATION: Winter resident.
NOTES: 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.
ESSAYS: Cooperative Breeding; Hoarding Food; Parental Care; Monogamy; Island Biogeography; Interspecific Territoriality.
REFERENCES: Koenig and Mumme, 1987; Stacey and Bock, 1978.

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Except for Stanford Locations, the material in this species treatment is taken, with permission, from The Birder's Handbook (Paul Ehrlich, David Dobkin, & Darryl Wheye, Simon & Schuster, NY. 1988).