Bald headed mynas
I am only a sometime-ornithologist and one that looks mainly at dead birds. I don't know the real reason why mynas appear bald-headed at times. Our local myna expert, Dr Kang Nee, noted this phenomenon of botak (Malay for bald-headed) Common Mynas (Acridotheres tristis) when she studied them in the late 80s and early 90s. She noted that birds that have their crown feathers actually do not have the yellow skin on the head. It's only when the feathers are gone that the skin turns yellow. Why? Don't know. Did the feathers drop off because of moult or fighting? Don't know. She never obtained any observations even though she spent several years studying and radio-tracking them in the wild and breeding them in captivity.
I have also written to the world's leading sturnid expert, Dr Chris Feare many years ago about botak mynas. He knew about them but couldn't offer any explanations either.
I think it might not be typical moulting, otherwise all Common Mynas would have the botak head at every moult cycle, which is usually once a year, and you should see a very high percentage of botak birds in the myna population.
Do mynas that are timid and smaller get pecked on the head until they are botak or do birds become more timid after they become botak? I have no answer. I wish I could lay my hands on some of these botak birds so that we may learn something from them.
Contributed by Wang Luan Keng in response to queries about these strange birds