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 transmitters we use on Ospreys weigh just a bit over an ounce and are attached like a backpack on the bird, as can be seen in this photo.
     They are solar powered and should last up to three years.


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.)
      The new generation of transmitters include a tiny GPS unit that records hourly locations, altitude, speed, and direction. Every three days the data are downloaded via satellite.


     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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