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

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

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)

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)

Wild populations

• Variable
• Average life expectancy (Watson 2010; Table 55, p. 295)
  • Estimates from Europe
    • About 11–40 years
  • Estimate from California
    • 11–13 years
• Another modeling study estimates 20 years (Whitfield et al. 2004)

Managed care

• No AZA estimates

• 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)