Acorn Woodpecker

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Acorn Woodpecker

• Melanerpes formicivorus

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Physical Description

• 65-90 g
• 13-15 cm wing span
• Clown faced
• Distinctive red crown
• Black and white head
• Glossy
• White eye area
• Males and Females roughly the same size

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Immature Description

• Hatchlings
• Naked
• Pink Skin
• Feathers begin to grow at 10 days
• Relatively poor coverage at 21 days
• Males and females have red crown (which looks
  like adult males) when young
• Basic Plumage appears 2-4 months after hatching
• Definitive plumage finalizes roughly 9 months
  after hatching

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Male v Female
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Geographic Range
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Home Range

• Along the west coast of the United States
• Interior hills and valleys of Oregon
• Various mountain ranges in California
• Not in coastal regions
• Ranges nearly to the Mexican boarder
• Throughout Western and Southern New Mexico
• In the mountains of Trans-Pescos Western Texas
• Pacific slope of Mexico through to central
  Chiapas
• Southern Guatemala
• Northern El Salvador
• Central Honduras
• Costa Rica
• Columbia

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US Population Map
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Migratory patterns

• It is not typical for populations do not migrate
  great distances
• When there is a great reduction of the major food
  source of insects, the birds rely on stored
  acorns
• If the stores run out, birds will wander away in
  search of food, but typically stay close enough
  that they can return the following spring
• One population is known to migrate
• From the Huachuca Mountians in SE Arizona
• This group stores acorns in natural holes, and
  expends them quickly
• It is belived that they then migrate South to the
  Sierra Madre Oak forests
• Adults return in the sping and occupy the same
  territory they left
• Young leave in the fall independently

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Food Habits

• Staples include
• Insects (Flying ants and other Hymenoptera and
  Coleoptera)
• This makes up approximately 23 of their diet
• This is the preferred source of food
• Arthropods will be eaten anytime they are
  available
• Acorns (Both directly from the tree and those
  that have been stored)
• This makes up approximately 53 of their diet
• They are eaten whenever arthropods are not
  available, typically from storage
• Fruits (Anything that they can find)
• This makes up approximately 23 of their diet
• Sap (Sap sucking is done in communal groups,
  birds congregate at particular holes that have
  been used for multiple years)
• Nestlings typically eat Arthropods, with
  increasing amounts of acorn fragments as they
  grow older

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Food Storage

• Some captured insects are stored in cracks or
  crevasses in trees
• Acorns (and sometimes other nuts) are stored in
  individually drilled holes
• This behavior is unique to the species, and is
  what gave the birds their common name

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Food Storage Diagram
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Mating and Nesting Systems
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An Overview

• Varies greatly from population to population
• Ranges from Cooperative polygyny to cooperative
  polygyny-polyandry
• Groups typically are made up of 1-7 male breeders
  and 1-3 female breeders
• Some groups also have up to 10 nonbreeding
  helpers to practice cooperative breeding
• Mating typically begins in April, peaking by the
  end of the month, and continues through June

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Courtship, etc.

• Courtship plays little role in mating
• Pair bond is not exhibited in the usual
  definition of the term
• Many nonmigratory populations live and breed in
  the same territory
• Inter-group mating is rare

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Nest Location

• Hastings Reservation
• Birds prefer east-facing holes on the undersides
  of slightly inclined, living, medium-sized oak
  limbs where temperature extremes are most
  buffered (Hooge 1989)
• New Mexico
• Cottonwoods and ponderosa pines are preferred.

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Nest Layout and Construction

• Typically cut out of the largest trees available
• Interior diameter 15 cm
• Depth Average 40 cm
• Height from ground Average 8.3 m
• 50 chance that any given nest will be reused by
  a particular bird

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Clutch Size and Egg Appearance

• Clutch 5.06 1.06 eggs
• Eggs
• White
• Smooth
• No Markings
• Translucent to begin, but turn opaque later

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Parental Characteristics

• Time spent incubating eggs
• Peeping begins after approximately 10 days
• Complete hatching within 12 days
• Brooded by all adults in a given group
• All group members help to feed chicks
• Breeding males clean the nest area

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Social Behaviors
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Social Behaviors

• Practice cooperative breeding
• Dominance relationships are established
• Most often between mating males
• Groups attack nest competitors
• Such as the European Starling
• Groups mob larger animals who attempt to steal
  stored acorns