Hello Arthur,
To tell the truth those were my thoughts also. But, to tell more of the truth I thought the overall coloring and markings indicated a species that should be nowhere near Bhutan, namely the adult female Temminck's Sunbird
Aethopyga temmincki. so I didn't dare to suggest that. However, spurred on to more careful researching, I noticed in Helm's SUNBIRDS guide that this was formerly "included in
A. mystacalis and known as Scarlet Sunbird." And, further, I found that
Aethopyga mystacalis Scarlet or Javan Sunbird is included in The Checklist of The Birds of Buthan (sic)...., here
http://www.birdlist.org/buthan.htm
Altitudinally, Helms records occurrence up to 1,985m.
However, the pale areas above and below the eye and into the lores are more in keeping with the
illustration (nothing in written description) in Helms guide of Fire-tailed, but everything else more with Temminck's.
You were absolutely correct about the male Fire-tailed not (usually)helping with nest building!!
I hope someone who really knows comes along soon.
Regards,
Marie