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Golden Eagle (Aquila chrysaetos) Fact Sheet: Reproduction & Development

Golden Eagle (Aquila chrysaetos)

Courtship

Courtship (Kochert et al. 2002)

  • Assumed to mate for life, but little data to verify this. (Kochert et al. 2002) (Watson 1997)
  • Resident, non-migratory populations keep pair bonds year-round (Bergo 1987) (Gordon 1868)
    • Copulation occurs all year, but most often before egg laying
  • Obvious courtship behavior is rare (Watson 1997)
  • Pre-nesting behaviors include:
    • Territorial defense
    • Aerial displays
    • Carrying material to nest
    • Vocalizing

Reproduction

Nesting (Watson 1997)

  • Nest in cliffs in mountainous areas; tree nests built in flat landscapes (Watson 1997)
  • A pair of eagles may have several possible nests, up to as many as 12 (Watson 1997)
  • Golden eagle nests characterized by small sticks; bald eagles construct with medium and large sticks (Watson 1997)
  • Leafy twigs or tufts of conifer needles used to line the nest (Baicich & Harrison 1997)
  • Nesting season (from egg-laying to independence of young) lasts over 6 months (Kochert et al. 2002)
  • Orphaned chicks can be placed in foster nests as long as they are still covered in down feathers (Garcelon & Bogue 1977)
    • Feathered chicks may be viewed as intruders and killed

Egg laying

  • Eggs laid at 3-4 day intervals

Eggs

  • Average egg size: 74.5 x 58 mm (about 3.0 x 2.3 in)
  • Egg weight: 142 g (0.3 lb)
  • Clutch size: 1-3 creamy white eggs with small brown spots
  • Incubation period: 43-45 days
  • In a study at Snake River Birds of Prey Area, southern Idaho: (Collopy 1984)
    • Females incubated eggs more often than males
    • Only females incubated at night
    • Males main task was to provision females with food
  • Incubating adults arrange twigs around breast feathers, perhaps to insulate eggs below (Ellis 1979)

Life Stages

Nestlings (Collopy 1984) 

  • Nestlings semi-altricial (need care); downy; eyes open (Baicich & Harrison 1997)
  • Brooding, shading, and feeding of nestlings done by female; male delivers food
    • Females stop nighttime brooding around 29 days
    • Females roost on nest until young around 40 days old
    • Females supplement male prey items by bringing prey to nest during 2nd week, gradually increasing prey up to 7-9th week, then gradually reducing
    • At 34-37 days, nestlings pull meat from prey carcasses, about the time they can stand
  • Nestlings may distance themselves from brooding parent, even when offered shelter from inclement weather (Ellis 1979)
  • Parents fold feet, then shuffle towards offspring in nest; sometimes adults step on young but folded feet minimize accidental piercing (Ellis 1979)
  • Nestlings have difficulty scratching their head with a foot and usually loose their balance (Ellis 1979)
  • Fledge between 66 and 75 days (Collopy 1984) 
  • Fledglings remain at nest site for a few weeks (Baicich & Harrison 1997)
  • For protection of nest sites from human impact, some 300 m (984 ft) should constitute a protective zone (Miller 2002)

Young

  • After fledging, young remain weak flyers for about 3 weeks (Baicich & Harrison 1997)
  • During first year, eagles in far northern locales of North America may migrate thousands of kilometers to wintering grounds (MyIntyre et al. 2008)
    • Young Denali National Park's golden eagles do not migrate at same time as the breeding adults
    • Young who remain behind in extreme northern latitudes often die during their first winter
  • Young become as heavy as adults in their first year. (Palmer 1988)

Adults

  • Adult plumage develops by 5th year
  • Sexual maturity delayed until at least the 4th year; more likely 5th year with full adult plumage (Watson 1997)

Longevity

(del Hoyo 2005)

In managed care

  • Up to 50 years

In the wild

  • 38 years in wild

Mortality and Health

  • Other than humans, no natural predators.
  • Previous causes of death have declined, especially DDT related
  • Wind turbines (Hunt 2002)
    • In a study lasting 88 months in California, 52 of 257 monitored eagles died of wind turbine blade strikes
  • Occasional deaths of males engaging in combat over nesting territories (Newton 1979)
  • Nestling mortality by avian predators is rare; may happen if food is scarce and female needs to be off the nest during incubation period (Watson 1997)
  • Nestling mortality from exposure to extreme temperatures, especially too much heat. (Mosher 1976)

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