Catching geese
Catching wild greylags is harder than you probably think. Urban geese can usually be caught with nothing more than a loaf of cheap bread. Wilder birds in rural areas (the ones we're interested in) are usually much more wary. We catch these birds using a large whoosh net (link to photograph), fired by heavy elastic over a baited area. Typically, we have to bait for several weeks to encourage geese into the catching area.
Catching wild birds in Britain requires a license issued by the British Trust for Ornithology. The staff involved in catching and handling birds are fully licensed to do so.
Tags & Tagging
All the birds we catch are fitted with a British Trust for Ornithology leg ring. If the bird is re-captured or found at any time, this unique identifier means that the bird's life history can be tracked. Ringing is the source of much of the data used in deciding how best to conserve birds.
For our project, geese also get a Microwave Telemetry Inc 70g GPS PTT tag. 
with a VHF radio tag attached, and most of them also have an orange collar with a unique letter code (photo).
The satellite tags incorporate a GPS receiver similar to the one your satnav uses. The tag takes a GPS reading every two hours, 24 hours a day, and these readings are logged in memory on board. Every third day, the tag contacts the ARGOS satellite network, and uploads its data via the satellite to ARGOS's computers in France. We can then access the records via the internet. We store them in a large database, which is also the source of the data you see on the web page. The satellite tag is solar-powered, so it should continue to work indefinitely, although the number of fixes obtained tends to drop off in gloomy winter days.
The VHF tag transmits constantly (not just every two hours). This means that we can track it down and find it at any time. This is useful if we want to find the bird and see what exactly it's up to, or if the goose drops the tag. By following the VHF signal, we can track it down (even underwater) and retrieve it.
The collars allow us to identify our bird in a flock at a distance, without approaching and disturbing them. This means that we can study the bird's behaviour without affecting it.
Anser geese in general are well-equipped to damage, destroy or remove radio tags of all kinds, and they do so regularly! We've had our tags beefed up to try to resist their attempts to destroy them, with stronger casing and antennas. We've also had to develop tougher harnesses, as the geese were able to nibble through them. We're now using a combination of a polyester and Kevlar tape with a Teflon outer layer to give strength and abrasion resistance, combined with comfort for the bird and light weight.