Variable Seedeater and Thick-billed Seed-Finch appear virtually identical but the seedeater is noticeably smaller with a curved culmen while the seed-finch has a more straight culmen. I am pretty certain these shots are of a male Variable Seedeater in the rain. Tiny bird.

photos taken in the rain in low light conditions

Rancho Bajo at
Rancho Naturalista,
Cartago Province,
Costa Rica
11 February 2016
9.8337
-83.5666
2610 ft elevation