It could well be a Clay-coloured Thrush. Looking through my photos I see that they tend to be much paler brown than this bird, but it could be affected by shade. In any case, there is a lot of variation. I have attached a picture (second photo) of one that is at the duller end of the spectrum and similar to the Costa Rican bird. I was also looking at the throat markings and many Clay-coloured Thrushes have streaking that is similar to the Costa Rican bird.
Nearly all the White-throated Thrush photos in my collection show a very clear yellow orbital, but the one attached (first photo, taken in January, so not a juv) does not seem to show it (assuming I did not make a mistake in the identification of this bird, which I am starting to think is a real possibility). The eye of the Costa Rican bird is a bit covered over, but clearly does not show the distinctive eye ring seen on most White-throated thrushes (see third photo).
I'm coming round to Clay-coloured, but still not 100% sure.
Tom
All photos taken in El Salvador - 1 by John Jackson, 2 by me, and 3 by Leti Andino