I intended to make this second part of the Blyth’s/Claudia’s/Davison’s Leaf Warbler Identification trilogy more about the behaviours of each species, but as Dave has pointed out in the first part that maybe I should explain more about the undertail pattern, so here I put a few more photos to show how the undertail pattern of each species is different from another.
From left to right: Blyth’s Leaf Warbler (ssp. assamensis), Claudia’s Leaf Warbler and Davison’s Leaf Warbler
As you can see, the undertail pattern of Blyth’s and Claudia’s are very similar; i.e. pale grey with clear-cut white border. If you look closely, you might also notice that Claudia’s has slightly less amount of white than Blyth’s, while Davison’s has completely white undertail (or actually almost completely as the outer web is grey).
The trick is always try to take continuous shots as these birds often flick back and forth showing both front and rear sides continuously.
Another photo showing the undertail pattern of Blyth’s Leaf Warbler. Even a poor shot like this can help confirm the identification.
And here’s another undertail shot of a Davison’s Leaf Warbler. Note the completely white undertail feathers.
But always be careful! A slight distortion of light or angle can totally change the look of the undertail feathers. This Claudia’s Leaf Warbler somehow shows completely white undertail feathers in this photo taken with external flash.
But the very same bird appear to have typical Claudia’s undertail pattern from a different angle, so take LOTS of photos. It helps!
Now let’s move on to the behaviour of each species. As I have said earlier that this is also very helpful for identifying these birds as each species has quite different way of feeding. I will start with Blyth’s and Claudia’s because they are the most confusing pair plumage-wise, but when it comes to feeding behaviour, they can be separated quite easily.
Blyth’s Leaf Warbler is pretty much a normal phylloscopus warbler, feeding by hopping from twig to twig looking for small insects among and under the leaves and such, but it doesn’t really hover. In fact, I have never seen one hovering.
Claudia’s on the other hand, has a very unique way of feeding. It loves clinging on tree trunks and branches just like nuthatches! You can just tell when you see one. It amazed me when I saw my first Claudia’s Leaf Warbler. It just went on climbing up and down the tree trunks and also both vertical and horizontal branches exactly like nuthatches.
And because of this, Claudia’s usually appear long-necked and slender-built because they always try to look out for food under the tree trunks and branches while climbing. On the other hand, Blyth’s and Davison’s rarely appear long-necked because they don’t do that.
But be careful, Blyth’s also sometimes perch on vertical branches hanging a little upside-down like in this photo, but they would normally skip on to the next branch shortly, not climbing along the same branch like Claudia’s mostly do.
As for Davison’s, I’ve never seen one exhibiting any nuthatch-like behaviour. Its behaviour is very much typical phylloscopus-like; i.e. hopping around from twig to twig and also occasionally hovering.
Among the 3 species, Davison’s is the only one that I’ve seen hovering similar to the Lemon-rumped Complex.
Another behaviour that many people seem to use for identification between Blyth’s and Davison’s is the wing-flicking behaviour. According to Robson’s guide to birds of SE Asia, Blyth’s flicks only one wing while Davison’s flicks both. Per Alström also mentioned about this characteristic in his article published in Forktail 9 (Link to the article). Personally, I think this notion of wing-flicking is quite misleading because it doesn’t seem to be true for foraging birds. I supposed that this characteristic is only true for birds at their breeding territories, but unfortunately I’ve never observed one, but many people have been using this characteristic to identify birds even while they’re feeding which I find very misleading because I’ve observed both Blyth’s Leaf Warblers that flicked both wings while foraging and Davison’s that flicked only one wing while foraging. Just like the individual below, which flicked both wings at a time but is clearly a Blyth’s Leaf Warbler according to the undertail pattern.
The undertail pattern confirms that it is a Blyth’s Leaf Warbler.
Same here for this individual which also flicked both wings.
While this one shows a typical textbook behaviour; i.e. flicking only one wing.
And this Davison’s clearly flicked just one wing too! So I would say that this characteristic is not very helpful for identification, probably only if seen at breeding territory which is still something that I need to prove for myself, maybe when I have time to stay in Thailand during spring and summer. In case you want to make sure that this one is a Davison’s, just scroll up to the photo number 5 from the top, that’s the undertail view of this individual.
For the next post, I will finish up with some notes about the songs of each species and also some odd birds that I find interesting. Stay tuned!