Geography Reference
In-Depth Information
soft, dark, cotton bag to calm and constrain. We weigh each bird in the bag and
then reach in to grip and extract it for additional measurements—beak dimen-
sions, wing length, and tail length—and to note signs of past injury, breeding
condition, parasitic l ies and mites, and overall health. Finally, we band the
bird's legs with a unique sequence of plastic color and metal numbered rings
that allow us to quickly identify each individual with binoculars. We record
all this information in i eld notebooks and later enter it into computer data-
bases. If we recapture a bird, such as the towhee in 2006, we measure every-
thing again and record these data. The senior towhee actually was 20 percent
heavier in 2006 than when I i rst tagged him in 2002; perhaps his weight in-
crease was a consequence of a new nearby bird feeder or an abundance of
bugs and berries. It probably helped him through his only doubly productive
year. If we only resight the banded bird, as I did with the towhee in 2007 and
2008, the color bands allow us to note where the bird currently lives, coni rm
its survival, and, with further observation, document its reproductive output.
Netting and trying to resight banded birds year after year allows us to esti-
mate a bird's lifespan and put annual reproduction into a lifetime perspective.
The lifespan of a small songbird in subirdia is surprisingly long. The ma-
jority of birds live less than one year, but some live much longer. The longev-
ity record set by the towhee of at least nine years was closely followed by other
towhees that lived at least six or seven years. One song sparrow matched the
old towhee, living to be at least nine years old. We also banded Pacii c wrens
and Swainson's thrushes that lived at least seven and eight years, respectively.
The oldest juncos, Bewick's wrens, and robins we encountered were at least
six. Most of these record holders lived either in forest reserves or in the places
we studied during their transition from forest to neighborhood. In these
places, the adult birds we recaptured—meaning that they were already at least
two years old when we banded them—lived an additional two years on their
territory. Apparently, though some birds move during construction, others
stay put—for life!
