Lemon-Rumped Tanager, aka Flame-Rumped Tanager

The lemon-rumped tanager is a subspecies of the flame-rumped tanager, but is considered a species by some authorities. Males are mostly black with a yellow rump (the rump is red in the nominate subspecies and is actually prettier). It has a black-tipped pale bluish bill. 

Male

Females have a black-brown head, wings and tail with mostly yellow underparts (the rump, vent and chest are orange-red in the nominate subspecies and again, it is much prettier). 

Female

Female and male

Juvenile: prettiest of all with a mixture of yellow, black and brown. 

It is found relatively close to the Pacific coast from a small portion of northern Peru up through Ecuador, Colombia, Panama and into southern Costa Rica. I saw it in Ecuador in the Mindo Valley and at the Amagusa Preserve in Mashpi.