Alan Murphy / Acorn Woodpecker (Melanerpes formicivorus), Arizona

Tom Vezo / Acorn Woodpecker (Melanerpes formicivorus) female, Madera Canyon, Arizona

Tom Vezo / Acorn Woodpecker (Melanerpes formicivorus) female bringing food to nest cavity, Madera Canyon, Arizona

Alan Murphy/ BIA / Acorn Woodpecker (Melanerpes formicivorus) pair, Arizona

Glenn Bartley / Acorn Woodpecker (Melanerpes formicivorus), New Mexico

Glenn Bartley / Acorn Woodpecker (Melanerpes formicivorus), New Mexico

Alan Murphy / Acorn Woodpecker (Melanerpes formicivorus), Arizona

Norbert Wu / Acorn Woodpecker (Melanerpes formicivorus) male at nest cavity with female looking out, Monterey, California

Norbert Wu / Acorn Woodpecker (Melanerpes formicivorus) male and females on trunk littered with their holes, Monterey, California

Norbert Wu / Acorn Woodpecker (Melanerpes formicivorus) breeding group at nest cavity to communally take care of chicks, Monterey, California

Norbert Wu / Acorn Woodpecker (Melanerpes formicivorus) female in nest cavity, Monterey, California

Norbert Wu / Acorn Woodpecker (Melanerpes formicivorus) male and females at nest cavity to communally take care of chicks, Monterey, California

Scott Leslie / Acorn Woodpecker (Melanerpes formicivorus) females at feeder, Cave Creek Canyon, Coronado National Forest, Arizona

Scott Leslie / Acorn Woodpecker (Melanerpes formicivorus) female, Cave Creek Canyon, Coronado National Forest, Arizona

Tom Vezo / Acorn Woodpecker (Melanerpes formicivorus) female, Madera Canyon, Arizona

Tom Vezo / Acorn Woodpecker (Melanerpes formicivorus) female, Madera Canyon, Arizona

Tom Vezo / Acorn Woodpecker (Melanerpes formicivorus) male, Madera Canyon, Arizona

Tom Vezo / Acorn Woodpecker (Melanerpes formicivorus) male, southeast Arizona

Thomas Mangelsen / Acorn Woodpecker (Melanerpes formicivorus) female clinging to pine tree with acorn ladder, Cuyamaca State Park, California

Tim Zurowski/ BIA / Acorn Woodpecker (Melanerpes formicivorus) pair at nest cavity, Arizona

Sebastian Kennerknecht / Oak (Quercus sp) branch, part of a granary tree, with acorns placed there by Acorn Woodpeckers (Melanerpes formicivorus), Blue Oak Ranch Reserve, Bay Area, California

Sebastian Kennerknecht / Oak (Quercus sp) branch, part of a granary tree, with acorns placed there by Acorn Woodpeckers (Melanerpes formicivorus), Blue Oak Ranch Reserve, Bay Area, California