Still Adigala

In early August 2013 Assamo stayed very close to Adigala.  Although I have never been there, given the pattern of locations I'd guess the abattoir is on the western edge of town (Look back at the previous post).  Can anyone who has been to Adigala tell me where the abattoir is located?  Or can someone tell me what might be so attractive to this vulture out on what I think is called "Mosque Road"?

GPS locations of an Egyptian vulture around the town of Adigala, Ethiopia, August 2013.

Now for a little lesson about the data we get from the transmitter fitted to Assamo...

Two types of locational data are received: GPS and Doppler.  GPS locations are calculated by part of the transmitter on the bird's back.  It "looks" for satellites that are at known positions, then calculates from its position relative to those satellites its own location.  Doppler locations are determined by a series of moving satellites "listening" for a pulse from the transmitter on the bird's back.  Because the locations, paths and velocities of the satellites are known,  the Doppler shift in the pulse's frequency can be used to calculate the likely location of the bird.  The map below shows Doppler data (red) and GPS data (green)

Doppler (red) and GPS (green) locational data for Assamo in early August 2013.

You will notice a few features:  Doppler locations tend to be dispersed over a wider area.  This is because the Doppler system is less accurate than the GPS.  You may then ask: "Why collect the Doppler data?"  Well the main reason in this case is that the pulse used to calculate the Doppler location is also the means by which the GPS data that are held in the transmitter are transmitted to the satellite and on to us.  Using the Doppler system to calculate location also has the advantage of using less power.  While this is not so important when tracking an Egyptian vulture in Ethiopia because the bird is rather large and the transmitter is solar powered, it can make a difference when one is trying to track a smaller bird or using battery power only.  Thus, the really small satellite transmitters used to track things like cuckoos and Amur falcons, etc do not use the GPS system, but rely totally on the Doppler system to calculate bird locations.

Close up of locations around Adigala in early August 2013

The use of the transmitter pulse to transmit GPS data also results in many more GPS locations per Doppler location.  So, in the case of Assamo, a number of GPS locations will be calculated and stored on board the transmitter, then these will be transmitted via satellite to us, and the pulses used to transmit those data will be used to calculate a "Doppler fix".