Would a bird field guide to Thailand pretty much cover the Malaysian peninsula as well or is it worth getting a guide specifically for the Malaysian peninsula?
The Robson fieldguide to Southeast Asia is what you want. It covers the entire area but is light enough to carry easily. You will be somewhat lacking trying to use a Thailand guide for Malaysian birds - there is quite a bit of overlap, but a lot of species do not occur far enough up the peninsula to be included in a Thailand guide. https://www.amazon.com/Field-Guide-Birds-South-East-Asia/dp/1472916697
If you've already got a Thailand guide and just want a Malaysian one, then the following might be good (I haven't seen it - the reviews on this page are mixed). I'd stick with Robson myself. https://www.amazon.com/Field-Guide-Peninsular-Malaysia-Singapore/dp/0199639434
@Chlidonias thanks for that, Robson it is. I now have a reply next time I'm asked what I'd like for Christmas.
