We birded down river from the city of Requena along Supay Creek the morning of Tuesday, January 17, 2012. It was a treat to photograph a Yellow-crowned Brush-tailed Tree-Rat, Isothrix bistriata, that was peeking out of a tree hole, the entrance to its den, in a várzea habitat. Nocturnal and arboreal, it has grayish-brown upperparts, a brown to rusty-colored rump, pale yellow underparts, a pale streak from its nose to its crown, and a long tail covered with thick hair. The tail will break off if pulled. Ears are short and naked. Large eyes and long whiskers are evident. Temperatures were in the low 90's with overcast skies and high humidity.