The bald eagle (Haliaeetus leucocephalus) and the golden eagle (Aquila chrysaetos) are two of the most iconic eagle species in North America. Both are large, powerful birds of prey, but they differ in size, coloration, habitat, and behavior.
The bald eagle is the national symbol of the United States and is best known for its distinctive brown body and contrasting white head and tail. The golden eagle is less widely recognized, with its golden-brown plumage throughout. Comparing the sizes of these two majestic birds brings insight into their differing lifestyles and ecologies.
Body Size
On average, the bald eagle is larger than the golden eagle in most standard measurements.
| Measurement | Bald Eagle | Golden Eagle |
|---|---|---|
| Length (inches) | 30-43 | 27-33 |
| Wingspan (inches) | 72-90 | 66-84 |
| Weight (pounds) | 8-14 | 7-15 |
As the table shows, bald eagles are larger in total length and wingspan. However, there is some overlap in weight between the species, with very large golden eagles capable of exceeding the size of small bald eagles. Overall though, the greater dimensions of bald eagles confirm they are North America’s larger eagle species.
Differences in Females and Males
Another consideration when comparing bald eagle and golden eagle sizes is the differences between females and males. In both species, females are noticeably larger than males.
Among bald eagles, females weigh about 25% more than males. The average female bald eagle has a length of 35-37 inches and weighs 10-14 pounds, while the average male is 30-34 inches long and weighs 7-10 pounds.
The size discrepancy is even more pronounced in golden eagles. Female golden eagles are up to 45% larger than males by weight. An average female is 31-37 inches long with a 79-90 inch wingspan and weighs 9-15 pounds. Male golden eagles measure 27-32 inches in length, have a wingspan of 66-79 inches, and weigh 6-10 pounds.
Therefore, while the bald eagle is considered the larger species on average, a large female golden eagle could potentially exceed a small male bald eagle in size. However, on the whole, the bald eagle’s greater size is clear when comparing the species’ ranges and typical measurements.
Reasons for Size Differences
A few major factors contribute to bald eagles generally being larger than golden eagles:
Habitat Variation
Bald eagles primarily occupy areas near large bodies of water, including coastlines, rivers, and lakes. They mainly eat fish, which they swoop down to grab from the water surface. Larger size aids bald eagles in physically overpowering fish and carrying more weight in flight back to the nest.
Meanwhile, golden eagles inhabit open country and mountains. They rely more on mammalian prey like rabbits, ground squirrels, and even young deer. The golden eagle’s smaller, more compact build allows greater maneuverability when pursuing and striking fast-moving prey on land.
Regional Adaptations
Bald eagles only occur in North America, while golden eagles have one of the most extensive distributions of any eagle species worldwide. Across this immense range, golden eagles exhibit some slight geographic variability in size, reflecting local adaptation. The largest golden eagles are found in the northernmost populations, such as Alaska and Canada. Further south, reduced body mass facilitates coping with higher temperatures and drier conditions.
Dietary Advantages
Access to more abundant food resources also plays a role in the bald eagle’s larger size. As the bald eagle specializes in scavenging fish and waterfowl, there is an ample source of food to sustain its greater mass in aquatic regions. More limited prey availability for golden eagles in terrestrial habitats selects for a smaller build requiring less energy intake.
Hunting and Feeding
The size difference between bald eagles and golden eagles contributes to variations in their foraging ecology and behavior.
Hunting
The large bald eagle is well-adapted for hunting fish, up to 6 pounds in weight. With a 6-7 foot wingspan, bald eagles are also capable of handling sizable waterbirds such as herons, cormorants, geese, and gulls. In contrast, the moderately smaller golden eagle more regularly takes smallish mammals like hares and marmots weighing 2-5 pounds. However, giant golden eagles of the northernmost regions can kill prey up to 30 pounds, including reindeer calves and bighorn sheep lambs.
Feeding
Bald eagles and golden eagles have distinct feeding behaviors related to their prey types. Bald eagles utilize their massive bill to tear fish flesh, often feeding on carrion. Golden eagles employ their smaller, hooked bill to rip into mammal hides to access meat. Most mammal prey of golden eagles is taken live rather than scavenged.
Competition
The sized differences reduce competition between bald eagles and golden eagles for food resources. Bald eagles’ huge size equips them to hunt larger fish that golden eagles can’t handle. Golden eagles’ greater agility enables them to pursue nimbler mammalian prey on the ground compared to bald eagles. Separate hunting skills allow the species to largely partition food within overlapping ranges.
Breeding Comparison
From courtship rituals to rearing young, the sizes of bald eagles and golden eagles also impact their breeding biology.
Pair Formation
Due to the female bald eagle’s larger size, males must perform elaborate aerial displays to impress prospective mates. Soaring high and then plunging in dramatic dives tests the male’s fitness and flying prowess. Golden eagles engage in spectacular paired acrobatics, with the male and female repeatedly locking talons and cartwheeling together in freefall. The smaller male golden eagle can match the agility of the larger female this way.
Nest Site Selection
Bald eagles construct the largest nests of any bird, up to 13 feet deep and 8 feet across. Their huge nests are built from a deep base of large sticks, topped by softer branches and lined with grass. These immense structures can weigh over a ton and typically require sturdy trees near water able to support them. Golden eagles build similarly shaped but much smaller stick nests on remote cliff ledges or in trees in open country.
Egg and Chick Size
Female bald eagles lay 1-3 eggs which are about 3 inches long and weigh 5-6 ounces. Female golden eagles lay 1-4 eggs around 2 inches long and weighing about 4 ounces. Given the mother’s greater size, bald eagle chicks and eggs are predictably larger than those of golden eagles. Both species hatch asynchronously, so the first chick is much larger than later hatchlings.
Fledging Period
Bald eagle chicks fledge at 10-14 weeks, somewhat earlier than 12-15 weeks for golden eagles. However, in both species fledging age depends more on growth rate than a set timeline. Parent eagles judge readiness by wing length and feather development rather than age. Generally the bald eagle’s greater size equates to a longer pre-fledging period.
Species Recognition
The distinct size and plumage differences between bald eagles and golden eagles make these raptors difficult to confuse in the field.
Identification Tips
Bald eagles sport unmistakable white heads and tails that contrast sharply with their chocolate brown bodies, identifying them unambiguously even at a distance. Golden eagles exhibit various shades of golden-brown plumage without white markings. At close range, bald eagles’ massive yellow bills are much stouter and heavier than the smaller hooked bills of golden eagles. In flight, bald eagles’ broad, flat wingbeats and straight-line soaring contrast with golden eagles’ rounded, splayed wingtips and buoyant flights. The bald eagle’s proneness to soaring over water also sets it apart from the golden eagle’s propensity for hilltop perching.
Geographic Ranges
Some overlap exists, but certain regions favor either bald eagles or golden eagles based on habitat. Bald eagles thrive mainly near northern aquatic habitats, reaching peak numbers in Alaska. Golden eagles frequent arid environments and uplands in the southwestern United States. The species segregate geographically where their differing needs dictate.
Rarity
Bald eagles are vastly more numerous than golden eagles, especially in the lower 48 states. With around 300,000 bald eagles and 60,000 golden eagles in North America, bald eagles are 5 times more abundant. Seeing a golden eagle is a special event compared to the familiarity of bald eagles near many waterways.
Conservation Status
Both eagles experienced population declines linked to pesticides like DDT and habitat loss. However, recovery programs have helped restore numbers, particularly for bald eagles.
Current Populations
The bald eagle population has quadrupled since 2009 to around 316,700 birds. The species was removed from Endangered Species Act protection in 2007. Golden eagle numbers are estimated at about 60,000 in western North America. While still below historical levels, their populations are considered stable.
Legal Protection
In the U.S., both eagles receive safeguards under the Bald and Golden Eagle Protection Act. This law prohibits killing, selling, or otherwise harming eagles, their nests, or eggs. Permits are required for activities that may disturb nesting birds. Additional legal defenses bolster bald eagle populations, while golden eagle monitoring and habitat conservation are ongoing.
Threats
Bald eagles face threats from lead poisoning, collisions with vehicles and powerlines, and human disturbance. Wind energy facilities could increasingly impact golden eagles through turbine strikes. Maintaining suitable habitat and food resources remains a challenge for both species. But continued protections should foster future security.
Conclusion
The bald eagle is adapted to being the larger of the two eagle species. Its great size suits its lifestyle of fishing and scavenging near waterways. The golden eagle is smaller and built for agility to capture fleet-footed mammals in open landscapes. Though the bald eagle typically exceeds the golden eagle in measurements and mass, there is some overlap, especially with females. But on the whole, the bald eagle’s dimensions make it North America’s largest eagle. Continued conservation efforts for both these majestic and ecologically important species will be critical to preserve our national symbols for generations to come.
