Modern technology is
revolutionizing how we study the world around us. Satellite telemetry is one of
the great new tools we can use to study animal migration. The first transmitters
that were used in studies of animal migration were so large that they could only
be put on things like bears and caribou. Within the past two
decades, the
transmitters have been miniaturized to the point where we can use them on birds
of prey. In the past few years GPS transmitters have
revolutionized the revolution. Because we now get data with accuracy measured in
meters, rather than kilometers, we can now answer ecological questions--where
are the birds hunting, how big are their home ranges?--that we could only wonder
about before.
Prior to the development of these new, small
transmitters, most of what we knew about bird migration was based on bird
banding.
| The Transmitter
With a satellite transmitter, we
get locations from our tagged bird every day, enabling us to follow a
bird's exact route from the breeding grounds to wintering area. We can
tell when and for how long birds stop en route. This enables us to
identify important places where the birds may need special attention. |
|
| The Satellite
The transmitters
we used prior to 2007 were
not GPS units, but rather
simply radio transmitters that sent some basic
information about the transmitters' operation to one of a series of
satellites traveling in circum-polar orbits. The satellites relay the
signals down to a computer in Maryland. A computer figured out where the
signal is coming from using some complicated program that relies on Dopler
shifts of the transmitter's frequency. (Dopler shifts are what make sirens
sound different when they're coming at you from what they sound like when
they're moving away from you.) |
|
Trapping
From 2000 to 2004
we trapped mostly
adults. We tethered a tame Great-horned Owl near the nest of the pair we
were trying
to trap. Ospreys hate Great-horned Owls, They're not alone in this, in fact the
only birds that don't hate Great-horned Owls are other Great-horned Owls. Owls
are most justifiably seen as a threat to the young in a bird's nest. The parents
will dive at the owl in an attempt to drive it from the area.
We string a couple of very fine, nylon nets around the
owl. If all goes as planned, the Ospreys dive into the nets in their efforts to
drive the owl away. When they hit the net, their momentum pulls the net off the
poles and they become entangled in it. We are right on hand to pick the bird up,
get it out of the net, and outfit it with its transmitter. The whole tagging
process takes less than an hour.
In 2004 we began tagging young Ospreys, shortly after
they began flying. To do this we put a carpet of nooses (tied out of fishing
line) on the nest. When the birds alight on the nest, their feet get tangled and
they can't fly away. We go up a ladder, or climb the poles with spurs and remove
them from the noose carpet. As of 2008 we have tagged 22
young Ospreys from South Carolina to Cape Cod.
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