Radio tags provide highly individual and intimate insights into the rovings of birds, such as this young Red Kite (main photo); as the technology evolves, the size of the transmitters continually decreases (inset).
71 : Radio tag
1973
Radio tags provide highly individual and intimate insights into the rovings of birds, such as this young Red Kite (main photo); as the technology evolves, the size of the transmitters continually decreases (inset).
Ringing is reliant on refinding marked birds, which have average recovery rates of less than 0.18 per cent. This fact alone means that huge numbers have to be ringed for any statistically meaningful result to emerge. Radio and satellite transmitters have changed all that by enabling individual birds to be tracked constantly throughout their travels – probably the most revelatory technological breakthrough in ornithology.
Tagging techniques, also known as telemetry, evolved from military use in the USA in the mid-20th century. The technology was first deployed in wildlife research in the early 1960s. The first radio frequency identification device (RFID) was patented by Mario Cardullo in 1973, and enabled individuals to be identified and tracked.
The techniques have been highly useful in determining migration strategies, habitat use, population levels, intra- and inter-specific relationships and survival capability. Spatial tracking methods include VHF (Very High Frequency) radio tracking, Ultra High Frequency (UHF) wavelengths and GPS (Global Positioning System) technologies on miniature Platform Transmitter Terminals (PTTs), battery-powered and carried by the bird. GPS locates devices to within a few metres by triangulating signals from three or four different satellites. Positional data can be stored in the digital memory of some devices or sent directly to a receiver or computer.
Cost and effectiveness mean that bird-tracking schemes are often funded by governments, for instance during the ‘bird flu’ scare, when satellite tagging was used to uncover possible H5N1 virus transport routes. Whooper Swans migrating from Russia to eastern Asia were expected to show a pattern comparable to the dispersal route of the virus, but tag signals showed their patterns and timings to be different. The human-contractable form of the disease was thus found to be more likely spread via the commercial movement of poultry from east to west by European factory farms.
The technique also has great conservation importance. The critically endangered Siberian Crane has had important stop-over sites in China on the way to its main wintering site of Poyang Lake identified by tagging, marked birds helping locate areas where resources and strategies needed to be implemented the most.
The distance, endurance, speed and survival abilities of birds have been well illuminated. Bar-tailed Godwits fly south from Alaska to winter in New Zealand and Australasia, travelling up to 7,258 miles almost non-stop over a nine-day trans-Pacific journey. On its hitherto poorly known migration, the secretive Great Snipe has been logged at an average ground speed of almost 56mph travelling from northern Sweden to tropical central Africa.
When a Hungarian-tagged Saker Falcon was tracked to Spain and then Mauritania before it was found dead, the species’ previously unknown wanderings – and therefore vagrancy potential to Britain – were confirmed, as were the dangers in dispersal and the necessity for cross-border conservation initiatives. Another raptor, a wayward European Honey-buzzard, was tragically tracked on computer screens as it attempted to migrate south-west from Britain, only for the signal to disappear in the Atlantic.
Perhaps the most publicly popular satellitetracking scheme to date is the BTO’s Cuckoo Tracking Project begun in 2011, where ‘sponsored’ Common Cuckoos are followed as they migrate to and from tropical African wintering grounds. Again, through this technology new routes were illustrated, as were the dangers facing long-distance migrants – by spring 2013, only four out of the original 19 young birds survived.
The technology is being constantly refined. Reduction in transmitter size is the way forward, preventing discomfort to the birds. The Avian NanoTag can weigh as little as 0.29g, measure 11mm and last several months; hundreds of birds can be assigned to one frequency, with individual details retained.
Clearly, as the technology gets smaller, more powerful and less expensive, new revelations can only continue to be forthcoming.