A tiny radio transmitter, fitted with a backpack harness that is designed to break free after several months. (©Scott Weidensaul)Besides banding, Weidensaul's crew has since 2000 been using radio telemetry to learn about how migrant saw-whet owls live when they aren't actively migrating. Each fall, owls are fitted with tiny, 2-gram radio transmitters about the size of pencil erasers, which are attached to the bird's body using a harness of thin, elastic thread designed to fall off after several months.

 The radios, while too small to permit researchers to follow the owls in in active migration, do allow the crew to locate them during the day. Almost nothing is known about what kind of habitat saw-whet owls use in migration, or what sites they pick for roosting – critical information for their A typical activity range for a northern saw-whet owl (©Ned Smith Center for Nature and Art)long-term protection and management. The main telemetry effort focuses on owls banded on South Mountain in Cumberland County, Pa., and which use the surrounding Michaux State Forest.

In 2008-09, the research crew also followed several dozen radio-tagged owls minute-by-minute through the night, building a detailed picture of the nocturnal hunting ranges of these tiny predators.