Morphological comparison of juvenile and mature Crested Serpent Eagle (Spilornis cheela)

Thong Chow Ngian made an interesting point-by-point morphological comparison of juvenile and mature Crested Serpent eagles (Spilornis cheela). Below is his photographic records of the species and the description of their differences.

Juvenile Crested Serpent Eagle at Goldhill Avenue

On 22 Jun 2021, I went to Goldhill Avenue to look for the juvenile Crested Serpent eagle (Spilornis cheela). It flew in at about 9.30am and perched on a tall tree, see Photo 1. Its appearance was new to me which I find fascinating. I have seen the adult eagles several times before, especially in West Malaysia, Borneo and also Pulau Ubin and the juvenile’s physical appearance took me by surprise.

 

                                 Physical differences between the juvenile and adult eagle

I would like to make a physical comparison between the juvenile eagle and the adult eagle in 3 ways: the front view, the side view and also the crest.

Photo 1. Young Crested Serpent eagle, Spilornis cheela.

 

Photo 2 shows the front views of the juvenile and an adult eagle. The obvious differences are the head and breast. The juvenile has a white forehead and white throat but the adult has a black forehead and black throat. Both birds have similar black ear coverts and yellow cere. The juvenile’s crown and nape are covered with scaly looking feathers but the adult is black. I will compare the crest feathers a little later. Another major difference is the breast feathers. The juvenile breast feathers are covered in scaly looking feathers but the adult bird is brown. The belly of both birds has white spots over brown feathers but the adult bird has more defined white spots.

 

Photo 3 shows the side views of both birds. If we exclude the differences which were already mentioned earlier, the biggest difference are the feathers covering the mantle, back and upper wing areas. The juvenile has dark brown feathers with whitish tips covering these areas but the adult bird is totally dark brown.

 

Photo 4 shows the differences of the crown and crest feathers. The juvenile bird has scaly feathers from its crown to the neck. The adult bird has a black crown, black crest with thick white bars and dark brown neck.

 

                                    Mobbing and aggression behaviours

I also observed that the juvenile eagle was constantly harassed by crows and 3 Oriental Pied Hornbills. They seem to be taking turns carrying out mock attacks. 

 

Photo 5 shows the juvenile bird mobbed by crows in the sky when it flew around the tree.

 

But when the juvenile eagle returned back to perch on the tree, the hornbills took turns to create a ruckus by yelling at the eagle and carried out mock attacks. 

However, the young eagle was no push over and held its ground.

 

Photo 6 shows the eagle puffed itself up to look bigger and displayed its aggression.

 

Photo 7. A few minutes later, it launched an attack at the hornbills. This caused the 3 hornbills to retreat, paused for a few minutes before taking flight and left the eagle alone.

 

It was indeed an interesting encounter with the juvenile Crested Serpent eagle.

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