Monkey-eater: Black-and-chestnut Eagle, Spizaetus isidori

Black-and-chestnut Eagle juvenile in our Cerro Candelaria Reserve, taken in 2010. Click to enlarge! Photo: Luis Recalde/EcoMinga.

I just came back from a camping trip in our largest reserve, Cerro Candelaria, with most of our staff and with Andy Orchard and Kendal Kempsey of Puro Coffee, the World Land Trust’s sponsors for the 2007 purchases which established the core of this reserve. I’ll write much more about this trip in a later post, but today I want to write about the most impressive bird we saw, the endangered Black-and-chestnut Eagle, Spizaetus isidori (formerly Oroaetus isidori). This gigantic eagle is the largest Andean eagle and the third-largest in Ecuador, after the immense Harpy and Crested Eagles. Our guards once saw it flying through the air with a monkey (probably a Capuchin) hanging from its claws. Over the last few days an adult and juvenile Black-and-chestnut Eagle were constantly flying around our campsite and cabin. They must have nested nearby. Now that the juvenile has left the nest, it spends a lot of time begging for food on conspicuous perches here. I managed to make a very brief video of its begging:

This is the juvenile Black-and-chestnut Eagle in the video. Photo: Lou Jost/EcoMinga.

This juvenile is mostly white with some brown mottling. Younger birds are even whiter. Over the course of several years, it will become progressively darker and darker until it attains the mostly-black adult plumage, with a chestnut breast. Here is my painting of the head of an adult:

My painting of an adult Black-and-chestnut Eagle.

This eagle is distributed along the lower and middle slopes of the Andes from Venezuela to Agrentina. It is a very scarce bird, with an estimated 200 adult birds in Ecuador and between 375-1500 adults throughout its range. It needs large tracts of good forest, where it hunts large birds such as guans, and mammals ranging in size from small squirrels to large and heavy Woolly Monkeys. Unfortunately it eats many chickens in areas where people have invaded forests, and this often earns it a death sentence. Our caretakers say they have solved this problem by letting turkeys run with their chickens; apparently the eagles are afraid of them. In 2014 the International Union for the Conservation of Nature (IUCN) raised its conservation priority status from Vulnerable to Endangered, “on the basis that its declining population is estimated to be very small, with fewer mature individuals than previously thought. The destruction of its montane forest habitat, as well as direct human persecution, are inferred to be driving a continuing decline.”

However, we seem to have a healthy population of these eagles. Our caretakers regularly encounter adults and juveniles in our Rio Zunac and Cerro Candelaria reserves, and I had found an active nest in the area in the 1990s. Here are some of the best photos that our staff have taken of these eagles in our reserves over the years:

Black-and-chestnut Eagle juvenile in our Cerro Candelaria Reserve in 2009. This is the first one that we were able to photograph well. Luis Recalde had to climb a tree to get the green background instead of a glaring sky. Photo: Luis Recalde/EcoMinga.

Black-and-chestnut Eagle juvenile in our Rio Zunac Reserve. Photo: Luis Recalde/EcoMinga.

Juvenile Black-and-chestnut Eagle in our Rio Zunac Reserve. Photo: Luis Recalde/EcoMinga.

Juvenile Black-and-chestnut Eagle watching us build a cabin in our Cerro Candelaria Reserve. Or was it trying to decide whether one of us could be dinner? Photo: Luis Recalde/EcoMinga.

Very close adult Black-and-chestnut Eagle in our Cerro Candelaria Reserve. Photo: Luis Recalde/EcoMinga.

As you can see, almost all of our best pictures are of the juveniles, who are less wary and often curious about humans. Our photos of the adult are not so good. Here is a great photo of the adult taken by Roger Ahlman (Roger has generously given us permission to use his photos on this blog) near our newest reserve, in northwest Ecuador. More about this reserve later….

Magnificent adult Black-and-chestnut Eagle near Chical, where we are currently making a new reserve. Photo: Roger Ahlman.

One of the most striking things about this eagle is its complete change of color from white to black as it gets older. Many other large birds of prey have nearly white juvenile plumages that persist after leaving the nest. In the Neotropics, the Harpy Eagle, Crested Eagle, and Ornate Hawk Eagle are good examples; some Old World eagles like the Changeable or Crested Hawk-Eagle also do this. See this link for a juvenile Ornate Hawk-Eagle in Costa Rica that looks very similar to the juvenile Black-and-chestnut Eagles, and this link for a very similar juvenile Crested Hawk-Eagle in Asia.

Eagles and New World vultures seem to be most closely related to a branch of the bird family tree that includes owls, trogons, toucans, woodpeckers, motmots, and jacamars. A surprising conclusion from DNA research showed that falcons, forest-falcons, and caracaras belong to a completely different group, closer to the parrots and songbirds (passerines). Detailed DNA analyses of the hawks and eagles are in their infancy, and we still have not yet been able to fully resolve their evolutionary history. However, one thing that has become clear through DNA analysis in the last decade is the close relationship between the Black-and-chestnut Eagle and the Neotropical species of hawk-eagle. Scientists used to put these birds into three different genera: Oroaetus for the Black-and-chestnut Eagle, Spizaetus for the Black Hawk-Eagle and the Ornate Hawk-Eagle, and Spizastur for the Black-and-white Hawk-Eagle. Recent DNA analyses clearly show that this classification based on superficial body characteristics was wrong. All these species actually belong in the same genus, Spizaetus.

Black Hawk-Eagle, closely related to the Black-and-chestnut Eagle. Photo: Roger Ahlman.

Ornate Hawk-Eagle juvenile. Wikipedia Commons.

Black-and-white Hawk-Eagle, another close relative of the Black-and-chestnut Eagle. Photo: Roger Ahlman.

The other large Neotropical eagles are not closely related to the Black-and-chestnut Eagle. The gigantic Harpy and Crested Eagles appear to belong to a very old lineage (some studies link them with Harpyopsis, the New Guinea Harpy Eagle).

Harpy Eagle juvenile. This is the most powerful eagle in the world. Photo: Roger Ahlman.

The two remaining large Ecuadorian “eagles”, the Solitary Eagle (Harpyhaliaetus solitarius) and Black-chested Buzzard-Eagle (Geranoaetus melanoleucus), are not really eagles and are closely related to the soaring hawks (Buteogallus, Buteo, and their relatives).

The Solitary Eagle, Harpyhaliaetus solitarius, is closely related to the soaring hawks rather than the other eagles. This one was in our Cerro Candelaria Reserve where it shares its range with the Black-and-chestnut Eagle. Photo: Luis Recalde/EcoMinga.

The Black-chested Buzzard-Eagle is really just a big powerful soaring hawk. Photo: Roger Ahlman.

For more detailed discussion of the phylogenies of eagles, see the following references:

Lerner, H. (2007) Molecular Phylogenetics of Diurnal Birds of Prey in the Avian Accipitridae Family.

Hering, E., Kvaløy, K., Gjershaug, J. O., Røv, N. and Gamauf, A. (2007)Convergent evolution and paraphyly of the hawk-eagles of the genus Spizaetus (Aves, Accipitridae) – phylogenetic analyses based on mitochondrial markers.

When looking at their phylogenetic trees, it is important to understand that they are very tentative, and their interpretation depends on what genes they used. Fast-mutating genes are useful for resolving relationships between closely-related species, but these genes no longer preserve much information about deeper relationships. Slow-mutating genes may reveal more about deep relationships, but might mislead about the topology of the shallower branches. Also, neither of these studies uses nuclear DNA, which is often more reliable.

Note that in the Hering et al study, there are two trees, which strongly disagree with each other in many places, and the Lerner tree disagrees with both Hering et al trees in many places. The Lerner tree looks more sensible to me.

Lou Jost

Black-and-chestnut Eagle juvenile in Cerro Candelaria Reserve. Photo: Luis Recalde/EcoMinga.