The Acorn Woodopecker, Melanerpes formicivorus is a species of woodpecker (Picidae).
Ant-eating woodpecker , Mearns' woodpecker , California woodpecker .
A black and white woodpecker. Black chin, yellowish throat, white cheeks and forehead, red cap.. Female has smaller bill than male and has less red on crown (top of the head) . In flight, it shows a white rump and wing patches that are conspicuous .
The acorn woodpecker mainly feeds on acorns. However, it will also feed on almonds, walnuts, and pecans; in California, in competition for food with Lewis's woodpeckers; during summer it eats mostly insects, often taken on the wing -- grasshoppers, ants, beetles, flies; also takes occasional fruit such as cherries, apples, figs, also green corn ; a major food especially in June and July is tree sap from small holes it drills in branches of live oaks  also from the holes dug by sapsuckers .
Its most common call is waka repeated several times; or, according to Peterson (1961), whack-up, whack-up, whack or ja-cob, ja-cob.