How can you tell a female acorn woodpecker?

A black band between the red cap and the white forehead

How does it catch most of its insects?

By chiselling grubs out of wood

Acorn Woodpecker

Melanerpes formicivorus

The acorn woodpecker (Melanerpes formicivorus) is a medium-sized woodpecker of oak woodlands from Oregon and California through Mexico and Central America to Colombia. Family groups drill trees full of small holes, called granaries, and store one acorn in each. It is one of the few birds in which several males and several females breed together in one group, helped by their grown-up young.

Acorn woodpecker abilities

50,000 holes in the biggest granaries
Acorn woodpecker families drill a tree full of small holes, then push one acorn into each hole to eat later.
- Each hole is about 1.3 cm wide and 3.8 cm deep, just right for a single acorn.
- Drilling never really stops. Most of it happens in winter, and every member of the group helps.
- As stored acorns dry and shrink, the birds move them to smaller holes so they stay snug.
- In one study in the southwestern US, groups with more than 3,000 holes had a 58% chance that their acorns lasted the winter. With fewer than 1,000 holes the chance was 9%.
Chance the acorn store lasts the winter
Granary over 3,000 holes58%
Granary under 1,000 holes9%
A study in the southwestern US, summarised by the US Forest Service.
Sources [2, 3, 4]
17 eggs recorded in one shared nest
Acorn woodpeckers raise their young as a team. Several breeding males and females can share one nest hole, and grown-up offspring help.
- A group can have up to 8 breeding males and 4 breeding females, plus up to 10 helpers. Most are much smaller.
- The females in a group lay in one shared nest hole. A typical clutch is 3–7 eggs, but up to 17 have been recorded.
- Before she starts laying, a female may remove eggs that another female has already laid. Once all the females are laying, this stops and the group cares for every egg.
- After about a week, everyone in the group takes turns keeping the eggs warm and, later, feeding the chicks.
Sources [1, 2, 3, 4, 10, 11, 12]
Apr–May when flycatching is its main way to feed
Most woodpeckers chisel grubs out of wood. This one waits on a high perch, then sallies out to catch insects in mid-air.
- At Hastings Reservation in California, flycatching is the main way it finds food in the nesting months of April and May.
- It hunts from stumps, treetops or branches just above the grass.
- Flying ants and their relatives, and beetles, are favourites.
- Insects are the main food for the chicks. Spare ones can be tucked under loose bark for later.
Sources [2, 3, 4]
>50% of its diet is acorns in California
Acorns are its main food, but it also sips tree sap and eats insects, oak flowers, fruit and nectar.
- In California, acorns make up more than half of what it eats. In Arizona and New Mexico they make up 25–50%.
- It drinks sap from small wells it drills in bark, or from holes made by sapsuckers. Sap holes are used again year after year.
- In California it sips sap from February to early March, and again from June to August.
- In the Andes of Colombia it seldom eats oak acorns, but it may often drink oak sap.
Sources [1, 2, 3, 4, 13]
ja-cob how field guides spell its loud call
Acorn woodpeckers are noisy birds, and their calls carry information: they know their family members by voice.
- Audubon’s field guide spells the loud call “ja-cob, ja-cob” or “wake-up, wake-up”.
- In playback tests, birds reacted faster to the calls of strangers than to the calls of their own group.
- They still knew the voices of old group mates that had moved to nearby groups.
- They even noticed when two outsiders from different groups seemed to call together, which suggests they keep track of who belongs with whom next door.
Sources [3, 14, 15]
1 band of black on the crown marks a female
Its bold black, white and red face is easy to learn, and the crown tells you whether you are looking at a male or a female.
- Look for a white forehead, a yellowish to white throat, black around the bill and a black stripe around the white eyes.
- Male: the red cap touches the white forehead.
- Female: a black band separates the red cap from the white forehead.
- In flight, look for a white rump and small white wing patches.
Sources [1, 2, 3]
30+ birds at the biggest battles
When the breeders of a top territory die, rival teams of brothers or sisters from nearby groups battle to take it over, and other woodpeckers come to watch.
- A dozen or more teams of three or four birds can fight at once. Radio tags showed some birds come back day after day and fight for up to 10 hours at a time.
- The biggest battles drew more than 30 birds, about a third of the woodpeckers in the area. Some travelled more than 3 km just to watch.
- Spectators spent up to an hour a day watching. Scientists think they are collecting news about their neighbours, but nobody knows for sure.
- These power struggles can last days or even weeks, and the largest team usually wins.
Sources [7, 16, 17, 18]
Stiff tail feathers with thickened shafts
Like other woodpeckers, it leans back on its stiff tail to brace itself against the trunk while it drills or stores acorns.
- The thickened shafts of the tail feathers work like a kickstand on an upright trunk.
- The feet grip the bark while the tail keeps the bird steady.
- Scientists study woodpecker tail muscles to learn how the birds hold still while clinging.
- The acorn woodpecker’s tail is wedge-shaped with pointed tips.
Sources [3, 8]

Tap a pin on the model or a part below.

- Males have a red cap that runs all the way forward to the white forehead.
- Females have a black band between the red cap and the white forehead.
- That one band is the easiest way to tell a male from a female.
Sources [1, 2]
- The head has a bold “clown” pattern: a white forehead, a yellowish to white throat and black around the bill.
- A black stripe runs around each eye and joins the black of the neck and back.
- Field guides describe it as a clown-faced woodpecker.
Sources [1, 2, 3]
White eyes in a black mask
- Adults have white eyes set in black, which makes their stare stand out.
- From high perches they watch for flying insects, then swoop out to catch them.
Sources [2, 3, 4]
1.3 cm wide storage holes
- The bill drills storage holes about 1.3 cm wide and 3.8 cm deep, each made for one acorn.
- In a 1979 high-speed film of a drilling woodpecker, the bill hit the wood at about 6–7 m/s.
- Unlike most woodpeckers, the acorn woodpecker rarely chisels into wood to hunt insects.
Sources [3, 4, 5]
- Like other woodpeckers, it has a long tongue that can reach out thanks to a special set of bones and elastic tissue.
- In a woodpecker scanned with X-rays, these tongue bones (the hyoid apparatus) had four sections joined by three joints.
- The acorn woodpecker mostly catches insects in the air or sips sap, so how much it uses its tongue reach has not been studied much.
Sources [1, 3, 4, 6]
- In flight it shows a white rump and a small white patch on each wing.
- Its wings are broad and rounded, and its flight dips up and down.
- It uses them for swooping, acrobatic flights to catch insects in mid-air.
Sources [2, 3]
73 g average weight
- It is black above and across the chest, with a white belly.
- An adult weighs about 73 g on average, about the size of a robin.
- Scientists track some birds with tiny radio tags worn on the back like a climbing harness with a bum bag, so they can follow them minute by minute.
Sources [2, 3, 7]
- Woodpecker tail feathers have thickened shafts. They act as a prop that keeps the bird steady on an upright trunk.
- Its tail is wedge-shaped with pointed tips.
Sources [3, 8]
- Woodpecker feet are built for gripping upright tree trunks.
- It rarely goes down to the ground, except to pick up grit and fallen acorns.
Sources [2, 8]
50,000 holes in the biggest granaries
- A granary is a tree or post drilled with storage holes, one acorn per hole. The biggest have up to 50,000 holes.
- The same granaries are used year after year, and new holes are added all the time.
- Granaries can be in oaks, pines, redwoods, palms, utility poles, fence posts, pine cones and even the wooden trim of buildings.
- A DNA study found the valley oak acorns in a granary came from only about 4–8 trees on average.
Sources [2, 3, 4, 9]

Real acorn woodpeckers

Photos from Wikimedia Commons. Some of them can repaint the 3D model.

At a granary tree in Chico, CaliforniaPhoto: Frank Schulenburg, CC BY-SA 4.0
MaleBlack back and chest, white belly and rump, white forehead and white eyes. The red cap reaches right to the white forehead.The crown is the only easy way to tell the sexes apartA male in cloud forest in Panama. Photo: Charles J. Sharp, CC BY-SA 4.0
FemaleThe same clown face, but a black band separates the red cap from the white forehead.Females in one group lay their eggs in a shared nestA female in Chocó, Colombia, near the southern end of the range. Photo: Charles J. Sharp, CC BY-SA 4.0
Storing acorns at a wildlife refuge in OregonPhoto: Megan Nagel / USFWS, Public domain
A granary packed with acornsPhoto: Raresvent, CC BY-SA 4.0
MaleBlack back and chest, white belly and rump, white forehead and white eyes. The red cap reaches right to the white forehead.The crown is the only easy way to tell the sexes apartA male at his granary in Solano County, California. Photo: Becky Matsubara, CC BY 2.0
MaleBlack back and chest, white belly and rump, white forehead and white eyes. The red cap reaches right to the white forehead.The crown is the only easy way to tell the sexes apartResting on a park bench at Atascadero Lake, California. Photo: Kevin Cole, CC BY 2.0
FemaleThe same clown face, but a black band separates the red cap from the white forehead.Females in one group lay their eggs in a shared nestA female stopping for a bath. Photo: Kevin Cole, CC BY 2.0
Busy at the granaryPhoto: Mark Gunn, CC BY 2.0
Eating an insect in Sonoma, CaliforniaPhoto: Sarah Stierch, CC BY 4.0

Acorn woodpecker by the numbers

Measured by field biologists, many from a study running since 1968.

Weight: 73 g; average adult, about the size of a robin⁠[2, 3]
Granary holes: Up to 50,000; in the biggest granaries, one acorn per hole⁠[3, 2, 1]
Storage hole: 1.3 × 3.8 cm; typical width × depth⁠[4]
Breeders in a group: Up to 8 ♂ + 4 ♀; plus up to 10 helpers; most groups are smaller⁠[10]
Eggs: 3–7; per clutch; up to 17 in a shared nest⁠[3, 1]
Incubation: 11–14 days; the whole group takes turns⁠[3, 4]
First flight: 30–32 days; after hatching⁠[3, 4]
Battle shifts: Up to 10 h; of fighting a day in a territory war⁠[7]
Spectator trips: >3 km; travelled by some birds just to watch a battle⁠[7]
Population: ≈7.5 million; estimated number of acorn woodpeckers⁠[3]

Acorn woodpecker myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“Acorn woodpeckers eat their acorns as soon as they find them.”
“Drilling a granary kills the tree.”
“Like most woodpeckers, it drills into wood to find insects.”
“Several females can lay their eggs in the same nest.”
“Woodpeckers travel kilometres just to watch a territory battle.”
“A bigger group always means more chicks for each bird.”
“A granary can be a utility pole or a house.”
“The size of a male’s red cap shows how important he is.”

Acorn woodpecker records

Superlatives from decades of field studies, each checked against its source.

Biggest acorn store
50,000 holes
Granary trees
one acorn per hole, in granaries used for generations⁠[3, 2]
Most eggs in one nest
17 eggs
Joint-nesting females
laid by more than one female in a single shared nest⁠[3, 1]
Biggest breeding teams
8 males or 4 females
Hastings Reservation groups
the largest breeding coalitions seen; most are 1–3 birds⁠[10]
Biggest battle crowds
30+ birds
Territory wars
about a third of all the woodpeckers in the study area⁠[7, 16]
Longest daily battles
Up to 10 hours
Fighting coalitions
and some birds came back day after day⁠[7]
Farthest trip to watch
>3 km
Spectators
travelled just to watch a power struggle⁠[7]

A year in the life of an acorn woodpecker

From sap season to the big acorn harvest, for a family group in central California.

Feb–Mar
Sap season
Birds sip sap from small wells drilled in oak bark.⁠[4]
Spring
One shared nest
Females lay about one egg a day in a single nest hole lined with wood chips. The group uses just one nest at a time.⁠[2, 20, 4]
11–14 days
Team incubation
At first one male and one female sit on the eggs. After about a week the whole group takes turns.⁠[4, 3]
Apr–May
Flycatching time
Insects caught in the air are the main food for the chicks.⁠[4]
30–32 days
First flight
The young leave the nest and are still fed by parents and helpers. Many stay on as helpers for years.⁠[3, 10, 18]
Jun–Aug
Summer sap
Sap season returns. Some groups raise a second brood.⁠[4, 1]
Sep–Dec
The big harvest
For 4–6 weeks the whole group gathers acorns and stores them in 1 or 2 granaries.⁠[4]
Winter
Living on savings
They eat stored acorns, drill new holes and move shrinking acorns to smaller ones. The size of the autumn acorn crop matters more than anything for next spring’s nest.⁠[4, 2, 21]

Acorn woodpecker vs red-headed woodpecker vs great spotted woodpecker

The red-headed woodpecker is a close cousin in the same genus. The great spotted woodpecker is the familiar woodpecker of British gardens.

Acorn woodpecker vs red-headed woodpecker vs great spotted woodpecker
	Acorn woodpecker	Red-headed woodpecker	Great spotted woodpecker
Scientific name⁠[22, 23, 24]	Melanerpes formicivorus	Melanerpes erythrocephalus	Dendrocopos major
Lives in⁠[2, 25, 26, 27]	Oak woods from Oregon to Colombia	Eastern North America, from the Rockies to the Atlantic	Woods, parks and gardens across Britain and Europe
Average weight⁠[2, 25, 27]	73 g	About 70 g	78.7 g
Main foods⁠[4, 25, 26, 27]	Acorns, flying insects, sap	Insects, nuts, seeds and fruit	Insects under bark, seeds and nuts
Breeding⁠[10, 25, 26]	Groups with several breeders and helpers	Pairs, thought to be monogamous	Nests from April to June
Nest⁠[20, 25, 26]	One shared hole for the whole group	A hole both parents drill, mostly the male	A newly drilled tree hole
Eggs⁠[3, 28, 27]	3–7 (up to 17 in a shared nest)	4–5 (3–7)	4–6
Sounds⁠[3, 28, 26]	“ja-cob, ja-cob” or “wake-up, wake-up”	“churr-churr” and “yarrow-yarrow”	Loud call and spring drumming
Population⁠[3, 28, 27]	≈7.5 million	≈1.8 million	≈130,000 pairs in the UK
IUCN status⁠[22, 23, 24]	Least Concern	Least Concern	Least Concern

Only the acorn woodpecker builds big shared granaries. The red-headed woodpecker hides food one item at a time in cracks it finds.

Are acorn woodpeckers endangered?

No. Acorn woodpeckers are common, but they depend on oaks and on big old trees for their granaries.

IUCN Red List

Least Concern (LC)

About 7.5 million birds from Oregon to Colombia. Counts rose slightly across the western US from 1968 to 1991, but fell in the Sierra Nevada.⁠[22, 3, 4]

IUCN Red List (BirdLife International)

Threats

Losing oak woodlands
Oak woodlands in Washington, Oregon and California are shrinking because of building, farming, logging, firewood cutting and conifers spreading where fires are kept out.⁠[4]
Sudden oak death≈50%
A tree disease caused by a water mould, Phytophthora ramorum, kills several oak species. One study estimated it could halve acorn woodpecker numbers in coastal California.⁠[4]
Wildfire and smoke≈14%
Between 2016 and 2020, about 14% of the acorn woodpeckers in the US lived where fires burned. On smoky days, birds stayed home and visited neighbours less.⁠[19]
Lost granaries
If a granary tree burns, rots or falls, or the acorn crop fails, a group may have to leave its territory.⁠[4]

What’s helping

Protected by law
In the US, the acorn woodpecker is on the official list of birds protected by the Migratory Bird Treaty Act.⁠[29]
Keep old oaks and dead trees
Acorn-producing trees, tree holes and standing dead trees are what it needs most. Leaving big oaks and snags standing helps.⁠[4]
Room for young oaks
Thinning crowded oak stands can grow future granary trees, and controlled burns can help young oaks.⁠[4]
Decades of watching
Scientists have followed colour-banded acorn woodpeckers at Hastings Reservation, California, since 1968, and count acorns on 250 marked trees each year.⁠[18, 21]

Other woodpeckers

Red-headed woodpeckerLeast Concern
A cousin from eastern North America, with about 1.8 million birds.⁠[23, 28]
Great spotted woodpeckerLeast Concern
A European woodpecker. In the UK its numbers grew by 373% from 1967 to 2024.⁠[24, 27]

Acorn woodpecker quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

How many acorns go into each granary hole?

Acorn Woodpecker field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

These clever birds eat mostly acorns and other nuts, but also enjoy insects, fruits, and tree sap.

Primary Foods

acorns
insects
tree sap
fruits
nuts
seeds
Foraging Method: Foraging

Ecological connections

Cooper's HawkEaten by
A hawk that preys on adult woodpeckers.
Red-tailed HawkEaten by
One of several hawks that can prey on adult woodpeckers.
Gopher SnakeEaten by
Preys on eggs and young nestlings in cavities.

Safety

Danger 1/5 · Very low

Always watch birds from a distance and don't disturb their nests.

Traits

Collections

Birds

Classification

Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Piciformes
Family: Picidae
Genus: Melanerpes

Sources for these acorn woodpecker facts

29 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Acorn Woodpecker?

Compare the silhouette, bill shape, tail length, wing bars and markings around the eyes. The same small brown bird at your feeder can look quite different in breeding plumage, winter plumage or its first year. Bird Identifier: upload a photo and compare the visible details.

How long is Acorn Woodpecker?

21-23 cm

What is Acorn Woodpecker's wingspan?

42-45 cm

How much does Acorn Woodpecker weigh?

0.065-0.085 kg

How long does Acorn Woodpecker live?

5-16 years

What does Acorn Woodpecker eat?

These clever birds eat mostly acorns and other nuts, but also enjoy insects, fruits, and tree sap.

Where is Acorn Woodpecker usually found?

Forests

Why do acorn woodpeckers put acorns in holes?

To save food for later. Each autumn the whole group stores acorns, one per hole, in a granary tree. The store feeds them through winter, and groups whose acorns last into spring nest earlier and raise more young.

How many acorns can a granary tree hold?

The biggest granaries have up to 50,000 holes, each holding one acorn. Groups keep adding new holes, so a granary grows year after year.

Do acorn woodpeckers damage houses?

Sometimes. They can drill storage holes in utility poles, fence posts and the wooden trim of buildings. They are protected by law in the US, so if they are a problem, an adult should ask a local wildlife agency for advice. Watch them from a distance and never handle one.

Why do acorn woodpeckers live in groups?

Granaries are hard to build and worth defending, so families stay together. Groups can include several breeding males and females plus grown-up young that help raise the chicks.

What sound does an acorn woodpecker make?

A loud, laughing call that Audubon’s field guide writes as “ja-cob, ja-cob” or “wake-up, wake-up”. The birds can recognise family members by their calls.

Do acorn woodpeckers really fight wars?

Yes, in a way. When the breeders of a good territory die, teams of brothers or sisters from nearby groups fight for it, sometimes for 10 hours a day over several days. More than 30 birds can gather, including spectators.

What do acorn woodpeckers eat?

Mostly acorns, plus flying insects such as ants, tree sap, oak flowers, fruit and nectar. In California acorns are more than half of the diet.

Where do acorn woodpeckers live?

In oak and pine-oak woodlands from Oregon and California through the southwestern US, Mexico and Central America to the Andes of Colombia. Most stay in the same territory all year.