Female black eagles, also known as female black-winged kites (Elanus caeruleus), are indeed larger than their male counterparts. This size difference is a common characteristic in birds of prey, where the female is often the larger sex.
The Size Difference Between Female and Male Black Eagles
In the case of black eagles, females are about 25% larger than males, weighing between 10 to 15 pounds, while males weigh between 6 to 9 pounds. This size difference is not only reflected in their weight but also in their overall body size, with females having a longer tarsus (lower leg bone) and deeper bills than males.
| Characteristic | Female Black Eagles | Male Black Eagles |
|---|---|---|
| Weight | 10 to 15 pounds | 6 to 9 pounds |
| Tarsus Length | Longer | Shorter |
| Bill Depth | Deeper | Shallower |
When observing a mated pair of black eagles, the size difference is usually noticeable, with males appearing smaller and more agile in flight compared to the more labored flight style of females.
Reasons for the Size Difference
Image source: Black Eagle by Mike Prince
The size difference between female and male black eagles is believed to have evolved independently in different orders of raptorial birds, including the black eagle. This size dimorphism is a common characteristic in birds of prey and is thought to have several advantages:
-
Prey Specialization: The larger size of female black eagles allows them to tackle larger prey, while the smaller males can focus on smaller, more agile prey. This division of labor can improve the overall hunting success of the pair.
-
Incubation and Brooding: During the breeding season, there is a division of labor between the sexes, with females taking on more of the incubation duties due to their larger brood patch. This makes them better suited to incubate clutches and brood small young, particularly during poor weather.
-
Territorial Defense: The larger size of female black eagles may also give them an advantage in defending the nest and territory from potential threats, such as other predators or competing pairs.
Behavioral Differences Between Female and Male Black Eagles
The size difference between female and male black eagles is also reflected in their behavior and hunting strategies. Females, with their larger size and more labored flight, tend to be more patient and methodical in their hunting approach, often waiting patiently for prey to come within range before striking.
In contrast, male black eagles are more agile and maneuverable in flight, allowing them to pursue and capture smaller, more elusive prey. They often employ a more active hunting style, actively searching for and chasing down their prey.
Conclusion
In summary, female black eagles are indeed larger than their male counterparts, with a noticeable difference in weight, body size, and incubation duties during the breeding season. This size difference is a common characteristic in birds of prey and is believed to have evolved independently in different orders of raptorial birds, including the black eagle. The size dimorphism between female and male black eagles provides advantages in prey specialization, incubation and brooding, and territorial defense, as well as influencing their hunting strategies and behaviors.
References:
- Amadon, D. (1966). Why are female birds of prey larger than males? Journal of Raptor Research, 9(1-2), 1-11.
- Nature – PBS. (2020, September 24). Bald Eagle Fact Sheet | Blog | Nature – PBS. Retrieved from https://www.pbs.org/wnet/nature/blog/bald-eagle-fact-sheet/
- Watts, B. D. (2018, January 8). Gender Divide in Bald Eagles – The Center for Conservation Biology. Retrieved from https://ccbbirds.org/2018/01/08/gender-divide-in-bald-eagles/.
