Rutland Ospreys

Scottish Ospreys

Technical Data

 

satellite tracking

Satellite tracking was used at Rutland between 1999 and 2001. The tracking as a way of discovering more about Osprey migration: what routes were used; what were the main hazards; what the pace of migration was- hours of flight per day, if there were any breaks in migration etc.; and how long migration took overall. It was also hoped that it would show us more about the wintering habits of Ospreys once they reached their final wintering sites in Africa. For Ospreys translocated to Rutland Water is was also important to make sure that the translocation did not affect their migration pattern, so tracking data was also taken from several Scottish Ospreys over the same period of time for comparison. The data below shows all of our satellite tracking results for Rutland and Scottish ospreys with a written description and an interactive map of each migration route. During the tracking each bird was given a tracking code (which appears at the top of the static maps) as well as a ring number. In the case of Rutland birds these numbers were usually the same, however the Scottish tracking codes were assigned regardless of ring number. To reduce any confusion this section uses ring numbers, rather than tracking codes, throughout. For more details of what happened to the Rutland Ospreys after their first migration please see the individual records page.

SATELLITE TRACKING DATA

Flights of Rutland juveniles

In 1999: 03(99); 04(99); 05(99); 06(99)
In 2000: 01(00); 02(00); 03(00); 04(00); 08(00); 09(00)
In 2001: 03(01); 04(01); 06(01); 10(01)

Flights of Scottish juveniles

In 1999: s6I(99)
In 2000: s3T(00); s12(00)
In 2001: s8H(01)
In 2002: sSK(02)

Flights of Scottish adults

In 1999: sSI(96); sJ(91); sHN(??); sXB(97); sSO(88)
In 2000: sJ(91); s8X(97)

 

TECHNICAL DATA- THE SATELLITE TRACKING SYSTEM

The system used is known as Argos and is provided by a French company called CLS - Collecte Localisation Satellites. This system can locate and receive data from so-called platforms anywhere in the world, on land or at sea. A platform consists of a radio transmitter, an antenna, a power supply and, possibly, sensors. Argos currently monitors several thousand platforms. These include moving platforms attached to birds and other animals, sailboats in ocean races, fishing vessels, drifting buoys (to measure ocean currents) and vehicles carrying hazardous materials. Static platforms which have sensors attached are used in remote or inhospitable places to monitor such things as the depth of water in rivers, the amount and type of snow in mountains and the noise coming from volcanoes to give advance warning of an eruption.

Click here to go to the Argos website where there are lots more interesting details about how the Argos system works.

The Argos instruments are flown on board the National Oceanic and Atmospheric Administration (NOAA). At least two of these weather satellites are operational at any time. They are on polar orbits at about 850km above the earth's surface. As the picture shows, each satellite is able to "see" platforms within a circle with a 5000-km diameter.However, the satellites are not stationary. They fly over the north and south poles, orbiting the earth once every 102 minutes. As the satellite proceeds in orbit, the visibility circle sweeps a 5000 kilometer swath around the Earth, covering both poles.

Due to the Earth's rotation, the swath shifts 25° west (2800 km at the Equator) about the polar axis on each revolution. each swath overlaps with the previous one but since overlap increases with latitude, the number of daily passes over a transmitter also increases with latitude. At the poles, the satellites see each transmitter on every pass, a total of roughly 28 times a day for two satellites.

The duration of transmitter visibility by the satellite (or of the pass duration over the transmitter) is the "window" during which the satellite can receive messages from the transmitter. It lasts about up to 14 minutes (10 minutes on average).

Diagrams and information were copied with permission from the Argos User's Manual.

The satellites receive the Argos messages from users' transmitters and relay them to regional receiving stations in real time. They also store them on tape recorders and read out ("dump") all the stored messages every time they pass over one of the three main system ground stations.

Once the data reaches a receiving station it is processed by powerful computers so that meaningful data representing the position of the platform can be sent to users.

the radio transmitters

BATTERY-POWERED TRANSMITTERS

Transmitter used in 2001. Manufactured by North Star Science and Technology, Baltimore, Maryland, USA	Battery-powered transmitter used in 1999 and 2000 manufactured by Microwave Telemetry, Inc of Columbia, Maryland, USA.

Two types of battery-powered units have been used during the project and they are pictured here.

These transmitters are slightly smaller than the solar-powered ones, weighing about 30g and being 1cm narrower. The transmitter is powered by a small battery which has a limited lifetime, estimated to be 750 hours. In order to conserve the battery as much as possible, the transmitter can be switched on and off at predetermined intervals. Each transmitter is programmed differently in order to provide as much useful data as possible about the carrying-bird's movements.

For example in 1999, for bird R03, a juvenile male translocated to Rutland Water, the transmitter was programmed to switch on for 8 hours and switch off for 6 days until the end of August - the assumption was that it would stay at Rutland Water until then. The pattern then changed to 8 hours on and 24 hours off for 45 cycles, by which time we expected it to have reached its winter quarters. For the rest of the battery's life, transmissions were programmed for 8 hours on and 10 days off.

By contrast, bird S06, a breeding adult female from Scotland, was fitted with a radio which would transmit every 2 days during the southward migration in order to be able to make more frequent transmissions during its expected northward migration the following spring.

The harness which attaches the radio to the bird is secured using bio-degradable cotton. This means that after two or three years, when the unit has ceased to function, the radio will fall off the bird's back.

SOLAR-POWERED TRANSMITTERS

In 2000, four of the young Ospreys translocated to Rutland were fitted with solar-powered transmitters. It is claimed that four hours of exposure to a bright sky is enough to power the transmitter for 24 hours. This type of transmitter should have given up to three or four years operating lifetime, enabling us to track juvenile Ospreys until they reached breeding age.

One of the solar-powered radio transmitters is pictured here prior to being fitted. It is attached to the bird's back using a carefully adjusted harness. The main part of the radio is often covered by the bird's feathers but the antenna, which is about 180mm (7 inches) long protudes through. These radio transmitters have been specially designed for use with large birds and do not impede their normal flight or lifestyle. They weigh 35g, about 2% of the weight of a small male Osprey. Because they are mounted on the birds' backs they do not hamper them when they enter the water, feet first to catch fish. 

Transmitter used in 2001. Manufactured by North Star Science and Technology, Baltimore, Maryland, USA	Roy Dennis' 'Beatrice' at Rutland Water, with transmitter clearly visible.

After release

After their release at Rutland Water, the birds carrying radio transmitters were seen flying strongly and making fishing attempts. The antennas could often be seen but ,after the first day or two, the transmitter itself was hidden by the feathers which had been rearranged by the bird.

Interpreting the data and drawing maps

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 -18:50 (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.

Data Accuracy

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.

External Use Of 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.