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Pallid vs Montagu’s Harrier - not just plumage

mai 18 2019

#Bird watching #GoBirding

Pallid vs Montagu’s Harrier - not just plumage

Birdwatchers tend to identify their birds usually either by plumage or by call (or both). Today there is a vast selection of fieldguides on the market and most of them focus on comparing and explaining plumage details. However, as we all know, when you really know a bird by heart, you often use other features to identify it, features which can be judged long before any plumage details are available. These features, often involving shape, structure, movement and behaviour may in certain situations be even more important than hard-to-see plumage details. Think about that next time you are watching a familiar, or a less familiar bird.

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Adult males of Pallid (left) and Montagu’s Harrier. Compare the difference in posture, with the longer legs of Pallid giving it a more erect stance, while the long wings and shorter legs of Montagu’s give it a more horizontal and elongated shape.

 

I regularly get pictures of birds sent to me for identification, mostly images of birds of prey. I remember one case, a perched raptor from the southern half of Africa, which had been circulated for a good while before it was sent to me.  The debate was whether it was a young Dark Chanting Goshawk or a young Gabar Goshawk. Both are brown above, have rather short wings, long legs and a long heavily barred tail, but the Chanter is about twice the size of a Gabar (which of course you cannot assess from a photo).

Anyway, as soon as I opened the image I realized that the bird is neither of the two! The plumage was kind of OK for both (the image did not show much fine detail as the bird had been a bit distant) but the structure was not! The bill was really heavy, yellow at the base with a dark tip, and the feet, although long, were strong with shortish and thick toes, while the hawks in question have thin legs and toes. The bird was in fact an immature Southern Banded Snake-eagle, which was identifiable by a suite of typically coloured and shaped bill, tall but strong legs, shortish wings and long tail. The plumage naturally confirmed the identification beyond doubt. I thought this was a good example of how misleading it can be to just focus on the plumage and forget about the rest.

 

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Juveniles of male Pallid (above) and female Montagu’s. Compare general proportions as described above for adult males. Note that iris colour reveals the sex in juveniles, yellow in males, brown in females.

 

Sometimes birds can actually be easier to identify by structure than by plumage. For instance the identification of the smaller “ring-tail harriers” (the juveniles and females of Montagu’s and Pallid Harrier) are notoriously difficult to id. in the field, because their plumages are not just similar but also variable. In this case comparing structures can be very helpful.

 

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Adult females of Pallid (above) and Montagu’s Harriers. Compare general shapes and proportions as explained above.

 

When perched on the ground the Montagu’s Harrier has comparatively longer wings, reaching the tip of the tail, while in Pallid the tail sticks out beyond the shorter wings. Also the legs of these two species are different giving them a different attitude when perched. In Montagu’s the legs are shorter which gives the bird a more horizontal stance and because of the long and attenuated rear the feet appear to emerge from the breast. Pallid Harriers have longer tarsi, which gives them a more upright stance and the feet appear to emerge further down on the underbody.

 

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Heads of juvenile male Pallid (above) and juvenile female Montagu’s. Compare the structure of the collar, how it completely encircles the neck in Pallid, almost in relief, while it is hardly discernible in Montagu’s.

 

The pale facial collar is often mentioned as a diagnostic feature when comparing these two harriers. However, the distinctiveness of this character varies both individually and depending on the age of the bird. If we for a while forget about the collar as a plumage feature and look at the feathers forming the collar instead, we can see that the shape of these feathers is different in Montagu’s and Pallid. Structurally this facial collar is equivalent to the outer edge of the facial disk of owls, and is formed by small narrow feathers, which are curved and almost spoon-shaped at the tip. In Montagu’s this special type of feathers are only found behind the ear coverts on the side of the head, while in Pallid they form a complete necklace around the throat and up along the sides of the neck. This means that even if you cannot see a contrastingly colored collar in, for instance, an adult female Pallid, you can still see in close views the structure of these oddly shaped feathers. The structured collar of the Pallid Harrier also explains why its head looks bigger and more rounded, more cat-like, while the head of a Montagu’s is slimmer and comparatively smaller.

 

Heads of adult female Pallid (above) and adult female Montagu’s. Compare details of collar as described above for juveniles.

 

About the author

Dick Forsman is a Finnish ornithologist, author, artist and travel guide. Dick's deep interest in birds, raptors in particular, started during his early childhood and ever since he has built his life around this passion. www.dickforsman.com

 

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