On 17 June and 20 June 2014 Zamek and his sister, J. Zamek, observed an adult Pygmy Nuthatch (Sitta pygmaea) feeding Mountain Bluebird (Sialia currucoides) nestlings near Prosser Creek Reservoir, Nevada County, California. The bluebirds’ nest cavity was approximately 2 m above the ground in a large snag. An active Pygmy Nuthatch nest with nestlings was in a cavity in the same snag approximately 2 m above the bluebird nest. There were other nest holes in this snag, but they did not appear to contain active nests. During approximately two hours of observation in late afternoon on 17 June and three hours in early morning on 20 June, a female Mountain Bluebird frequently fed the three bluebird nestlings. A male Mountain Bluebird was also present and remained close to the nest most of the time but visited the nest only four times on 17 June and twice on 20 June. A Pygmy Nuthatch also fed the Mountain Bluebird nestlings at least ten times on 17 June and at least nine times on 20 June. The Pygmy Nuthatch also reached into the Mountain Bluebird nest and removed fecal sacs two times on 20 June. Zamek obtained photographs of the bluebirds and the nuthatch feeding the bluebird nestlings and removing a fecal sac (see this issue’s back cover), making this one of very few photographically documented examples of interspecific feeding of nestlings and nest maintenance.