When Trevor Ford and I visited Kampung Permatang Nibong on 5 November, there were around 500 Eastern Yellow Wagtails swarming over a couple of fields, so we went back the following day for a closer look.
Unfortunately for us, there were only about 100 left, but that was enough to be getting on with!
The taxonomy of Yellow Wagtails is a quagmire! The current 'state of play' is as follows:
1. Eastern Yellow Wagtail (Motacilla tschutschensis): includes nominate 'tschutschensis' (formerly 'simillima' and 'angarensis'), 'taivana' and 'macronyx'.
2. Western Yellow Wagtail (Motacilla flava): includes 'thunbergi' (sometimes called 'plexa')!
In Peninsular Malaysia, it is thought that the 'tschutschensis' race of Eastern is the commonest form, followed by 'macronyx' and then 'taivana'. The status of 'thunbergi' Western Yellow Wagtail is uncertain because of the difficulty of differentiating it from M.t.macronyx, but both forms have been identified from museum skins as occurring in the area (Wells 2007).
According to Wells, first winters can be told from adults by having a yellow-based lower mandible.
Added to the mix is a potential addition to the Malaysian list - Citrine Wagtail - which looks quite similar to Eastern and Western Yellow, particularly females and first winters (see here). Perhaps the key feature to look for in a Citrine is a complete pale surround to the ear coverts.
A nice easy one to start with - a male 'macronyx'. The only yellow males we saw were of this race.
Can't say too much about this one. Is it a non-breeding female? Perhaps 'tchutschensis' due to the supercilium?
A very different looking bird...is all I'm going to say about this one!
This should be a first winter (pale bill base) but gender? race? Who knows?!
Some birds contravene the Trade Descriptions act altogether - not a trace of yellow on this "Yellow Wagtail"! Interesting pale blue-grey rump. This must be a first winter.
A couple more 'female types'. The lower bird shows distinctly white vent/undertail coverts, which, according to Robson, is a diagnostic field character of non-breeding male Citrine. Hmmm!
What I learned about Yellow Wagtails today is that I have much more to learn about Yellow Wagtails!