About the radio transmitters

BATTERY-POWERED TRANSMITTERS

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.

These transmitters are manufactured by Microwave Telemetry, Inc of Columbia, Maryland, USA.

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.