On 4 June 2005, while birding along the Chilikat River near Haines, Alaska, we observed a pair of Cassin’s Vireos (Vireo cassinii) attending an active nest. The birds were also observed later the same day by Thede Tobish, Jr., Alan DeMartini, and Gary H. Rosenberg. We first heard an adult singing at 06:00 hrs, and at approximately 06:30 hrs followed it to the nest, where it fed four young. We photographed the pair, nest, young (Figure 1), and surrounding habitat during the period of observation. The pair was actively feeding the young and disposing of fecal sacs during our visit. Both adults delivered food to the young, but they were seldom seen for more than a few seconds at the nest. When we approached the nest, both birds became agitated and gave alarm calls. After a short period of discontinuous singing in the early morning, the pair continued to vocalize solely with alarm calls until we departed after 0.5 hour of observation.