There is nothing quite like holding wild birds. Their beauty, colours and behaviour never fail to astonish: The blue tit, so common in the UK, turns out to be the most aggressive, pecky little bird imaginable; the goldcrest – the weight of a 20p coin (or a nickel for transatlantic readers) – so tiny; the sparrowhawk, quite a rarity to trap, with its murderous look and talons.
The chance of getting this close to wildlife was one of the factors that attracted me to the surprising and challenging world of bird ringing.
Long before dawn this winter morning, small groups of people all around Britain will wake up to spend several hours in the cold, in marshes, on beaches and sea cliffs. Their goal? To trap birds of as many species as possible in high nets, to measure them, age them, place a lightweight ring with a unique serial number on their right leg and release them, as part of a huge citizen science project which has lasted more than a century now.
Joining this project as a trainee, which I did a little more than a year ago, was a startling and rather humbling experience. It remains so. I’ve been a birder (not a twitcher, please) for many years, and thought I knew a fair bit about birds, at least in the British context. I could identify many dozens of different species by sight and by their song, even if there are always plenty of people in the bird hides who know more than me.
Actually I knew very little. The migration of birds to and from northern Europe from Africa, yes. The details of that migration, when, how they prepare for these extraordinary journeys, their numbers, how high they fly, no.
What was also a surprise to me was that hundreds of thousands of birds actually migrate to Britain in the winter – not just the geese that descend on Norfolk and other wetlands in such large numbers from even colder places such as Scandinavia, Iceland and Russia, but more everyday birds like robins and blackbirds.
We regard them as British birds, but actually their numbers swell considerably in the winter as their continental cousins come in from elsewhere in northern Europe. The reason why robins sing so much in the winter is because they’re defending their territory from “outsiders”.
The ringing scheme is intended to establish how these and other migration patterns are working, which birds are on the decline and on the rise. Retrapped birds provide important clues to the health of bird populations.
The serial number on their rings is matched to the last time the bird was caught, yielding information about how their weight, wing size, fat and muscle depth has changed.
More than a million birds caught every year
The age and sex of the bird in many cases can be gauged by their plumage (debates on tell-tale but minute graduations in colour take up a fair part of our mornings). So the data gathered by 3,000 volunteer ringers, from more than a million birds trapped in the UK and Ireland every year, plays a key role in conservation efforts.
For example, as a result of research done using ringing data, agri-environmental schemes were developed to provide winter seed for farmland birds, which are believed to have contributed to the partial population recovery of reed buntings, a bird that we often trap at our site in Surrey.
Another recent study at Grafham Water north-east of London gave valuable information about nightingales’ movements which helped plan management of the habitat at that Site of Special Scientific Interest.
When I say it’s an early start, I don’t exaggerate. In winter our ringing group arrives at the bird reserve two hours before sunrise, to put up the 10ft (3m) high mist nets. Some reserves have fixed nets that can be unfurled very easily. Ours are erected afresh each time (head torches indispensable here) because we move them depending on the season – no point putting a lot of nets up in the reed beds when the reed warblers are away until late April in sub-Saharan Africa.
Outside the breeding season we play sound recordings of the birds that we’re particularly keen to trap – if there’s a sighting of bramblings, then that goes on the player. And it makes a difference. The numbers of redwings we trapped went up considerably when we started playing a tape made in Latvia, one of the countries they migrate from during the winter.