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Predatory birds like eagles have a unique feature that scientists call “reverse sexual dimorphism,” which means the female of the species is typically larger than the male. Scientists have measured the weight, wingspan, talons and beaks of eagles in captivity and in the wild. Researchers have also captured eagles’ vocalization on recordings and observed behavioral differences between the sexes as well.
The male bald eagle weighs 5 to 9 pounds and the female easily outweighs him at 12 to 15 pounds. Steller’s sea eagle is the largest of the eagle family. The male Steller weighs a mere 11 to 13 pounds in comparison to the female’s 15 to 20 pounds. The African fish eagle female is over 56 percent heavier than the male. She weighs anywhere from 7 to 8 pounds while the male weighs 4 to 5 pounds. Another eagle heavyweight is the harpy. The male harpy weighs roughly 8 1/2 to 12 pounds. In contrast, the female weighs 14 to 20 pounds. A notable exception to the weight of female eagles is a harpy named Jezebel who weighed in at a whopping 26 pounds. Experts believe being housed in a zoo with food readily available caused her excessive weight.
An adult female bald eagle’s wingspan is larger than the male’s. She has a wingspan of approximately 7 feet, whereas a male’s is 6 feet 6 inches. The male Florida bald eagle has a shorter wingspan of only 6 feet. The female of the larger Alaskan bald eagle has a wingspan of 8 feet. The harpy has a wingspan from approximately 6 to 7 feet. Harpy wing measurement data is usually not broken down by sex, but The Cornell Lab of Ornithology says that the females are at the larger end of the wingspan spectrum. Female Steller’s sea eagles boast a massive wingspan of 8 feet. Although the male’s wingspan is shorter, it is still an impressive 7 feet.
Talons and Beaks
In a 1983 research program, Dr. Gary Bortolotti discovered through measuring the beaks and feet of newly hatched eagles and periodically remeasuring the same nestlings, he could predict their gender. Both male and female eagles have four talons. The rear talon is called a “hallux.” Female bald eagles have larger halluces -- the plural of hallux -- than males. Female bald eagles also have deeper beaks, measured from the top of the bill to her chin.
Near dawn, the male African fish eagle fish is at his noisiest, but the female rarely makes any noise at all. A male bald eagle’s voice is higher in pitch when compared to the female’s voice. The male harpy’s call has been described as a whispy scream or wail repeated five to seven times in a 30 to 40 second time frame with 10 second rests between calls, The Cornell Lab of Ornithology reports. The female harpy’s call is a shorter call but repeated more frequently at nine to 12 times. A female harpy was recorded making a “yelping” noise while her mate was making soft quacking noises like a duck.
Both the male and female harpies contribute to the building of the nest, but once the female lays eggs she is the primary incubator. The male will take over while she eats the food that he brings her. Both parents feed the nestling, but the female harpy brings more food to the nest. The female bald eagle initiates their elaborate courtship ritual. After the nest is built and eggs are laid, they share the incubation process. One sits on the nest while the other hunts for food. Steller's eagles are so reclusive that researchers have some information about the nests they built, but not much about their reproduction behaviors.
- AvianWeb.com: Harpy Eagles
- Oiseaux-Birds.com: African Fish Eagle
- San Diego Zoo: Birds: Steller’s Sea Eagle
- American Eagle Foundation: Eagle Biology - Reproduction
- AvianWeb.com: Bald Eagles
- University of Saskatchenwan: Criteria for Determining Age & Sex of Nestling Bald Eagles
- The Cornell Lab of Ornithology: Neotropical Birds: Harpy Eagle
- Tom Brakefield/Stockbyte/Getty Images