Harpy Diaries 6: Is the harpy eagle chick male or female ?

Well, let’s dig a bit into raptor ecology then...

• Raptors are a group known for having morphological adaptations to hunt and/or feed on carrion, so they have sharp eyesight, powerful claws to catch their prey, and a strong beak. Harpy eagles fit in a small class or group that tends to be called "forest raptors".
• Forest raptors have particular features. For example, they never soar over the forest canopy because they like to ambush their prey, usually other birds. Also, most of them have a barred chest, which allows them to camouflage among the branches, the foliage, and the contrasts between lights and shadows.
• Forest raptors also have reversed size dimorphism (RSD). This means that females are larger than males, and this difference is going to be more acute the faster and more agile their prey is. If a raptor is specialized in hunting blackbirds (like a goshawk) the difference in size between female and male is going to be proportionally bigger than if a bird is specialized in hunting sloths or monkeys (like harpy eagles).

Harpy eagle on a branch by Arturo Bullard

Why do males and females demonstrate RSD?

Well, nobody knows exactly why yet, but a couple of hypothesis are the most supported:

1. To avoid competition between males and females for the same prey (Kee Wai is able to prey upon big howlers and Baawaja is not, for example)
2. Males are smaller in order to be more efficient foragers in the breeding season, especially when the female is incubating the egg. That is because it is supposed to be easier to hunt on a larger number of small prey rather than bigger ones, which can assure a constant food supply for both female and chick (s).

So, this is the reason why the male, Baawaja, is smaller than the female, Kee Wai.

Now, our main question is - what gender is harpy eagle chick, Elpis?

We cannot know for sure, but take a look at the image below. That’s Elpis appropriating the prey that Dad brought (the video will appear later on) and you can notice that Elpis is at least the same size, if not slightly bigger than Baawaja.

Bawaaja and Elpis in the nest by Rainforest expeditions

Considering that our juvenile is still 6 months old, judging by size alone, it seems likely Elpis is a female.

Also,  our team here at the lodge, the guides, the staff, and us, the biologists, can recall the size of the previous chick, Jupiter.  He never got bigger than Baawaja (Dad) - that's how we knew he was a male. This comparison makes us even more convinced that Elpis is female,  although we still cannot prove it 100%.

Finally - let's look a bit at their daily life.  Elpis is getting more and more confident. Every day jumping and flapping her wings to become stronger, which allows her to fly properly.

This confidence is not only on a physical level but also in terms of behavior. Stay tuned, as we will see in the next video Dad delivering what seems to be a two-toed sloth and Elpis taking the dead body under her claws and protecting it in the same way Mom used to do in the past, with an aggressive display towards Baawaja.

We think that the harpy eagle chick, Elpis, learned that behavior from mom and is getting prepared to confront the new challenges of the forest on her own.

So what happened with the Female Harpy Eagle, the Mom?

Things are changing up there in the nest. Even Mom and Dad appear to have changed roles again because we haven’t seen the female mother, Kee Wai, in the videos for a couple of weeks.

Perhaps she is taking a break after having been in charge of 80-90% of chick feeding since the hatch (but remember that during the incubation period dad was the one delivering prey for both Mom and Elpis).

What could be happening? Regular duty- shift? Short break? Mom coming at night when we have our camera off? We will figure it out the next weeks when we finish analyzing the videos of the last month.

Read Harpy Eagle Facts Here