An earlier post by KC Tsang on the call of the Fire-tufted Barbet (Psilopogon pyrolophus) mentioned that the bird appeared to sing with its bill closed. At that time Janet, who was with him, also commented on this.
The posting attracted the attention of Dato’ Dr Amar-Singh HSS who had some doubts, “The call is definitely a Fire-tufted Barbet but I am not entirely convinced the bird in the video made it. Wells (1999) says ‘At the start of the call, body held horizontal but it rises near vertical as tempo increase.’ The bird in the video seems to be listening to the call made rather than making it.”
Amar referred to the Internet Bird Collection where there are a few videos of the barbet calling. Yes, these birds clearly have their bills open when calling. Amar may well be right. The Fire-tufted Barbet in the video may be listening to a call by another barbet rather than actually calling.
The question that needs to be answered is whether the Fire-tufted Barbet can call with its bill closed. And whether it can call with its bill opened or closed, depending on the circumstances.
All birds change their bill aperture frequently within a single song (Williams, 2001). And there are a number of species that call with their bill closed. In fact the Blue-eared Barbet (Megalaima australis) calls with its bill closed, as reported by Adrian Lim in an earlier post.
Field ornithologist Wang Luan Keng urges more field observations on vocalisation, not only on the calls and songs per se but on the behaviour of the birds when vocalising.
Williams, H., 2001. Choreography of song, dance and beak movements in the zebra finch (Taeniopygia guttata). The Journal of Experimental Biology 204, 3497-3506.