BAS biologists studying the movements of Macaroni penguins have, in the past, used radio transmitters on the birds to determine if a bird is out at sea or in its colony. This is expensive, intrusive and unreliable and can be deployed on only a limited number of birds.
To overcome these limitations a ‘gateway’ system has been developed. The gateway is constructed between the colony and the sea. Birds travelling between the two must pass through it. The gateway uses radio-frequency identification technology (RFID) to read the industry standard animal tags implanted in the birds. The system records the tag number, the time and the direction of travel of the bird. Time at sea and time in the colony can therefore be deduced.
Mains power is not available at the site so the system was designed to have low power consumption and is powered by a combination of solar panels and wind generators feeding rechargeable lead-acid batteries.
How the system works:
The system is divided into two halves positioned some 85 metres apart. The penguin end – the gateway and associated technology, and the human end – control computer, solar panels and wind generators. The Gateway is shown in the picture on the right. The computer and monitor are located in a field hut.
Studies on nesting seabirds which require repeated capture of individuals can cause disturbance and may have detrimental effects on their breeding success. This new automated logger gateway greatly reduces the necessity to handle birds during the study of macaroni penguin demographics on Bird Island, when the identity of individuals is required on a regular basis.
The gateway can record the movement of hundreds of individual penguins through an entire breeding season (impossible to do manually) yielding valuable information on the frequency and duration of foraging trips at sea, which in turn gives an indication of food availability.
Furthermore, although macaroni penguins are known to be monogamous and display high nest site fidelity, very little is currently known about their survival rates. By tagging a proportion of the chicks each year, you can monitor known-age individuals from several cohort years and thereby calculate survival rates. A number of one year old birds tagged as chicks in February 2003 are known to have returned to the colony in January 2004, as a result of being recorded by the gateway.
The system has three basic components. A control computer, optical retro-reflective detectors and the Texas Instruments XXXX RFID unit and antenna. The optical sensors are positioned such that a penguin passing through the gateway passes in front of, and therefore triggering the detectors. The detectors are connected to auxiliary inputs on the TIRIS reader and the computer continually polls the reader for the status of these inputs.
As soon as the computer detects that one of the opticals has detected a bird, it requests that the TIRIS reader start interrogating for a valid tag. When a tag is read it’s serial number is sent to the computer for logging. The logging and control computer – a low power PC104 format 386 PC is therefore running 24 hours a day, the TIRIS reader only when a bird is detected in the vicinity. In this way the power requirements of the system can be kept to a minimum.
The TIRIS tags have proved very reliable and easy to use and have been used by animal breeders of all types to tag anything from cattle to race horses to domestic pets and have been used for many years. The tags are sterilisable and the injection site is small enough not to require stitching