Acorn Woodpecker

Melanerpes formicivorus

Order:
Piciformes
Family:
Picidae
Sections

Systematics

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Female Acorn Woodpecker; San Diego, California, United States.

Presumably subspecies M. f. bairdi. Resident from southern Oregon south through northern Baja California. Adult female with nape red; forehead patch broad and white; throat pale yellow; chest solid black; black flank streaks broad; black mantle with green gloss; irides white.

© Nancy Christensen , California , United States , 12 November 2017
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Male Acorn Woodpecker; Monterey, California, United States.

Presumably subspecies M. f. bairdi. Adult male with crown red.

© Paul Fenwick , California , United States , 28 December 2017
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Female Acorn Woodpecker; Santa Cruz, Arizona, United States.

Presumably subspecies M. f. formicivorus. Resident from southern Arizona and New Mexico south through Mexico to the Isthmus of Tehuantepec. Center of chest is streaked black (not solid).

© Audrey Addison , Arizona , United States , 15 March 2019
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Male Acorn Woodpecker; Coconino, Arizona, United States.

Presumably subspecies M. f. formicivorus.

© Daniel Irons , Arizona , United States , 20 April 2018
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Female Acorn Woodpecker; Baja California Sur, Mexico.

Presumably subspecies M. f. angustifrons. Resident in mountains of southern Baja California Sur. Chest streaked black, forehead narrow and yellowish, and irides dark; averages smaller.

© Nigel Voaden , Baja California Sur , Mexico , 1 May 2015
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Male Acorn Woodpecker; Baja California Sur, Mexico.

Presumably subspecies M. f. angustifrons.

© Gerardo Marrón , Baja California Sur , Mexico , 8 February 2015
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Female Acorn Woodpecker; San José, Costa Rica.

Presumably subspecies M. f. striatipectus. Resident in the mountains of Costa Rica and Panama. Throat is deep yellow (not pale) and black mantle has a blue gloss (not green).

© Doug Beach , San José , Costa Rica , 26 April 2016
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Male Acorn Woodpecker; San José, Costa Rica.

Presumably subspecies M. f. striatipectus.

© Steve Mayes , San José , Costa Rica , 25 February 2019
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Female Acorn Woodpecker; Caldas, Colombia.

Presumably subspecies M. f. flavigula. Resident in the Andes of Colombia. Adult female with nape black.

© Jacob Drucker , Caldas , Colombia , 4 November 2018
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Male Acorn Woodpecker; Antioquia, Colombia.

Presumably subspecies M. f. flavigula. Adult male with crown black.

© Camilo Jaramillo , Antioquia , Colombia , 16 April 2019

Part of the melanerpine line within the genus Melanerpes (sensu 22). Most species in this group are found in Central and South America; in the United States it is also represented by the Red-headed Woodpecker (M. erythrocephalus), Lewis' Woodpecker (M. lewis), and possibly also the sapsuckers (Sphyrapicus spp.). Melanerpine woodpeckers use a wide variety of foraging methods, including mast storage, frugivory, flycatching, and sapsucking, but rarely if ever drill for subsurface insects in wood in typical woodpecker fashion. Many species exhibit cooperative breeding or other complex social behaviors (see Breeding: Cooperative Breeding).

Geographic Variation

Plumage pattern, size, and coloration of bare parts vary strongly across the species’ geographic range (20). Bill length increases clinally with latitude, whereas tarsus length, tail length, bill width, and wing chord are smallest in the desert Southwest and the southern tip of Baja California and largest elsewhere along the Pacific coast. Plumage varies considerably, albeit subtly. The saturation of yellow on the throat varies from deep in southernmost populations to whitish in lowland pine forests of the Caribbean slope to pale yellow in the north. Continuity of black on the breast band creases somewhat clinally from complete in the north to broken (i.e., streaked) in the south. Populations in southern Middle America—i.e., Oaxaca, Mexico, south to Panama—have a few red feathers on the chest, whereas those farther north and in Colombia are polymorphic for this character (20). Crown color of the adult male and nape color of the adult female is black in northern South America, and red elsewhere. Eye color is apparently dark in Baja California Sur, and white elsewhere, except among fledglings.

Subspecies

Seven subspecies, following Short (4) and Dickinson and Remsen (23) (cf. 24), diagnosed on the basis of variation in plumage color and pattern.

  • M. f. bairdi Ridgway, 1881. Includes M. f. martirensis (Grinnell and Swarth, 1926). Resident from southern Oregon south through northern Baja California [type locality = Petaluma, Sonoma County, California]. Adult male with crown red; adult female with nape red; forehead patch broad and white; throat pale yellow; chest solid black; black flank streaks broad; black mantle with green gloss; irides white.
  • M. f. angustifrons Baird, 1870. Resident in mountains of southern Baja California Sur [type locality = Cape San Lucas, Baja California Sur]. Broadly similar to M. f. bairdi, but chest streaked black, forehead narrow and yellowish, and irides dark; averages smaller.
  • M. f. formicivorus (Swainson, 1827). Includes Picus melanopogon Temminck, 1828; M. f. aculeatus Mearns, 1890; M. f. mearnsi (van Rossem, 1934); and M. f. phasma (Oberholser, 1974). Resident from southern Arizona and New Mexico south through Mexico to the Isthmus of Tehuantepec [type locality = Temiscaltepec, Estado de México]. Similar to M. f. bairdi, but center of chest streaked black (not solid).
  • M. f. albeolus Todd, 1910. Resident in coniferous lowlands from Belize to northern Honduras [type locality = vicinity of Manatee, Belize]. Similar to M. f. formicivorus, but throat whitish (not strongly yellow) and black flank streaks narrow or absent.
  • M. f. lineatus (Dickey and van Rossem, 1927). Resident from eastern Oaxaca south to Nicaragua [type locality = Mt. Cacaguatique, San Miguel, El Salvador]. Like M. f. formicivorus, but whole of chest streaked black (not solid laterally).
  • M. f. striatipectus Ridgway, 1874. Resident in the mountains of Costa Rica and Panama [type locality = Birris, Cartago, Costa Rica]. Similar to M. f. lineatus, but throat deep yellow (not pale) and black mantle with blue gloss (not green).
  • M. f. flavigula (Malherbe, 1849). Resident in the Andes of Colombia [type locality = Colombia]. Similar to M. f. striatipectus, but adult male with crown black and adult female with nape black.

Related Species

The woodpeckers constitute a well-resolved evolutionary unit, the family Picidae, characterized by zygodactyl feet, a lack of down feathers at all ages, stiffened rectrices, and chisel-like bills. There are 3 divergent subfamilies within the Picidae, the true woodpeckers (Picinae), the piculets (Picumninae), and the wrynecks (Jyginae), with a fourth, the Nesoctitinae, solely comprising Nesoctites micromegas (the Antillean Piculet), recognized at times (25). The Picinae is by far the most speciose of the subfamilies, accounting for 86% of the ~224 species in the family. Molecular studies (25, 26, 27, 28, 29) have begun to bring relationships within the Picinae into focus. The genus Melanerpes is phylogenetically near to Sphyrapicus, the sapsuckers (25, 30, 28, 29). These 2 genera are similar in voice, behavior, anatomy, and phenotype (31, 4).

Within Melanerpes, M. formicivorus apparently is sister to a clade that includes 2 South American species, M. candidus (the White Woodpecker) and M. cactorum (the White-fronted Woodpecker), and a species confined to a single island in the Lesser Antilles, M. herminieri (the Guadeloupe Woodpecker) (29).

Recommended Citation

Koenig, W. D., E. L. Walters, P. B. Stacey, M. T. Stanback, and R. L. Mumme (2019). Acorn Woodpecker (Melanerpes formicivorus), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.acowoo.02