Fulvous Whistling-Duck (Dendrocygna bicolor)

The Fulvous Whistling-Duck is a pretty duck, very similar in shape to the Black-bellied Whistling-Duck, to the point that it can be confused with a Juvenile of the Black-bellied. I was lucky because three individuals came to swim on the lake by Concasa, so I spotted them when I returned home in the afternoon. This was unexpected, because I already knew that they only inhabit the northwestern region of Costa Rica, and should be not be found in the Central Valley. I took out my camera and snapped lots of pictures, because I assumed the birds would leave next day. And so they did, in the days afterwards there was no sight of them. Since then, a single individual has returned a few times joining a flock of Black-bellied, which seems pretty unusual. I have seen the Black-bellied pecking at this Fulvous, seemingly trying to drive it away, but it stays with the flock.