Data arrived daily by electronic means from the Argos processing centre. Two examples are shown here.  |
Transmitter code - This data is for bird R03(1999). Latitude and Longitude - This is about 2.5 km from the release pens at Rutland Water. Accuracy class - a 0 indicates that the estimated accuracy for this data is more than 1000m. Date - day 222 in the year is 10th August . Time -1850(GMT) is 19:50 (BST). |
These data were then interpreted, compiled and published daily on this website by Barrie Galpin. In 1999-2001 he produced maps using the DMap mapping software.
The accuracy of the data
When we received data from Argos, it came with an accuracy class. We received a few calculated locations with an accuracy class of 3 (better than 150m) but most positions were less accurate than that. Some, for example, were classed as having "no estimate of location accuracy." In such cases we had to treat the position with extreme caution - some had to be rejected totally because they suggested impossible locations such as hundreds of kilometres out over the Atlantic. Another suggested that a bird was west of Leicester at a time when it was being watched by monitors as it sat in a tree at Rutland Water.
As we gained experience of interpreting the data we became more confident in knowing which data to reject. However, it remains the case that locations sometimes only made sense in retrospect and we then needed to revise a previously published interpretation. Generally we only published locations which came with an estimated accuracy.
The accuracy classes were determined by the number of transmissions received by one of the satellites in the 10 minutes or so as it passed over a bird. With only one transmission, no location could be calculated; the more transmissions the better the accuracy of the calculation. The calculation is done by comparing the small differences in frequency caused by Doppler effect - but that's another story!
And what determines the number of transmissions received? All sorts of factors are involved such as the position of the bird (is it in a tree, in a rocky gorge, flying etc), the relative position of the satellite (is it high in the sky or low over the horizon), atmospheric conditions etc.
If you are interested, all this is explained clearly on the Argos website here.
Revisiting the data and revising the maps
In 2006, the ready availability of much more powerful mapping software in the form of Google Earth gave Tim MacKrill and Roy Dennis the ability and incentive to revisit the original satellite data. Their new analysis of Osprey migration and wintering behaviour will be published as soon as possible. However, we decided to update the maps published on this website and make them generally available using Google Maps, and Barrie Galpin completed this in early 2007.
Unfortunately some website visitors do not have a fast enough internet connection or use a browser that does not support Java script, so they will be unable to enjoy panning and zooming to follow the flights of the tracked Ospreys. So for their sake, the old static maps are still available on a separate page alongside the information about the individual birds and commentary on the migration route. You need to click on "Description" on each bird's Google Map page.
We have now removed the previously published tables showing dates, latitude and longitude, and description of approximate location, as the new technology has shown that in some cases these location descriptors were incorrect.
External use of the data
By making some of the migration data available on the website we have put it into the public domain and available for others to use. We request that potential users who may be contemplating any publication that refers to the data, contact the Rutland Osprey Project team and also ensure that the project is fully acknowledged.