Geography Reference
In-Depth Information
every few seconds for three weeks. Kara would use a radio receiver dialed
into the transmitter's frequency to i nd the sparrow and make daily records
of its behavior, chart its location, verify that it survived the day or locate its
remains, and measure its habitat. After three weeks the radio tag's battery
would die, leaving us again in the dark about the bird's fate. Even later, the
cotton thread holding the harness together would rot, freeing the bird of its
high-tech butt pack. We watched the bird briel y in a box before letting it go.
Its movement was normal, the transmitter looked i ne, and we received a strong
signal from it on our radio. We returned our electric sparrow to its parents
and looked for another bird to tag. Over the course of two years, Kara caught
and radio tagged 122 newly l edged birds. She got over her nerves; the young
birds did not.
Radio tagging is a dei nitive, although labor-intensive, way to determine a
bird's survival. Each day that we i nd the bird, we know whether it is alive or
dead. Some days, a bird is AWOL, but mostly this occurs when a bird leaves
the study area, not when it dies. It seems we rarely lose track of dead birds;
I've pulled them out of irrigation pipes, dug them out of badger dens and veg-
etable gardens, isolated them in hawk nests, and extracted them from the gul-
let of a great-horned owl. (Okay, I didn't pull it from the owl's throat. Another
of my students studying young prairie falcons tracked one transmitter for sev-
eral days that was nearly fully swallowed by an owl until the predator coughed
up a pellet that included the functioning transmitter and a young falcon's
bones.)
Three weeks go by fast, but it was the best glimpse into a young sparrow's
life that technology could provide. Transmitters suitable for wrens and juncos
would last even less time, so we decided not to track them. Kara had a longer
window into the world of young Swainson's thrushes, towhees, and robins—
six, eight, and nine weeks, respectively.
Young birds are tough. Only 20 percent of radio-tagged birds died during
our study. Birds such as Cooper's hawks and mammals such as Townsend's
