Martial eagles (Polemaetus bellicosus) are Africa’s largest eagles, and they have unique adaptations to stay warm in cold temperatures. These adaptations include a specialized feather structure, a counter-current heat exchange system in their legs, and various behavioral strategies.
Feather Insulation
Martial eagles have a unique feather structure that helps them stay warm. They have two layers of feathers – a stiff exterior layer of covert feathers and a fluffy layer of down feathers underneath. The covert feathers zip together, creating an overcoat that channels water away from the eagle’s skin and down feathers, absorbs solar energy, and reduces energy loss. The down feathers trap and hold warm air, keeping the eagle toasty even in subzero temperatures.
When martial eagles are cold, they can erect and fluff out their feathers using a specialized muscle at the root of their body feathers. This increases the depth of the warm air surrounding them, further enhancing their insulation.
Counter-Current Heat Exchange
Image source: Martial eagle by Charles J. Sharp
Martial eagles have a built-in counter-current heat exchange system in their legs. The arteries and veins in their legs run close together, allowing cold venous blood returning to the eagle’s core to wick heat away from warm arterial blood flowing to its feet. This system keeps the eagle’s feet and legs from freezing or leaking too much heat, reducing its energy burden.
Behavioral Strategies
In addition to their physical adaptations, martial eagles also employ various behavioral strategies to stay warm in cold weather:
- Reducing Activity: Martial eagles will reduce their activity levels to conserve energy when it’s cold.
- Seeking Protective Microclimates: They will seek out and create protective microclimates, such as sheltered areas or roosts, to reduce their exposure to the elements.
- Manipulating Temperature: Martial eagles can adjust their body temperature by shivering or panting to regulate their heat production and loss.
- Foraging and Roosting in Groups: Martial eagles may forage and roost in groups, which can help them conserve heat and share resources.
- Gorging on Food: When food is scarce, martial eagles may gorge on food to increase their energy reserves and insulation.
- Increasing Food Assimilation: Martial eagles can increase their assimilation of food energy to stay warm in cold weather.
By combining their specialized feather structure, counter-current heat exchange system, and various behavioral strategies, martial eagles are able to thrive in the diverse habitats of Sub-Saharan Africa, even in cold temperatures.
