Entering the woods is like diving into a dappled sea of green. The rustle of leaves and sounds of birds fill the air. “That croaking sound is a raven. The cat-like mewling, a buzzard,” says ecologist Ben Sheldon. Blackcaps, wrens and robins are also making themselves heard, but we’ve come to Wytham woods near Oxford, UK, to visit some other birds.
This 4-square-kilometre tract of classic English woodland was in 1943 by a wealthy couple after the death of their beloved daughter, on the condition that it be used for teaching and research.
Four years later, biologist David Lack started a project that continues today. One of the pioneers of evolutionary ecology, he was looking for a population of wild animals that he could use to measure some basic parameters, such as lifespan and population size. The birds of Wytham woods – particularly its great and blue tits – were just what he needed. “At that time, some of the things we now take completely for granted about the way that wild populations work were not known at all,” says Sheldon. “It is amazing how little we understood.”
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Lack died in 1973 but his work goes on: the is the longest-running field study of birds anywhere in the world. “If there were a Nobel Prize for Ecology, and if you could award it to a place rather than a person, Wytham Woods would surely be a prime candidate,” wrote zoologist John Krebs, who worked at Wytham in the 1960s and is now president of the British Science Association.
Sheldon is the latest in a line of Oxford biologists to oversee the project. One reason tits are ideal to study, he tells me, is because they have a strong preference for breeding in nest boxes rather than natural cavities. Wytham has 1200 boxes, enough to house its population of about 700 breeding pairs of great tits and blue tits with room to spare. “Sometimes you open a box to find a bat looking at you, seeming a bit cross,” he says.
As we head to our first box of the day, Sheldon explains that having the birds exactly where you want them means they can easily be weighed, measured and tagged. He and his team tag up to 10,000 every year, many before they leave the nest.
This morning, one of the team has captured an adult. Sheldon deftly tags the bird, places it head first in a small plastic cylinder and weighs it. A moment later the bird is gone. They are very tolerant of being handled, Sheldon says.
“In human terms, this is like tracing bird families back to the Norman conquest“
Each bird gets two tags: a metal ring on one leg – the traditional approach – and a RFID tag on the other. Introduced to Wytham in 2007, RFID tags have revolutionised the collection of data, enabling the team to track the comings and goings of individual birds. “By the end of each year, we’ve got in excess of 15 million location/date points,” says Sheldon.
After almost seven decades, you might think surprises were hard to come by, but the advent of RFID and other technologies means that there are always new questions to ask.
Sheldon’s colleague Ella Cole recently took some tagged great tits into the lab to test their problem-solving abilities. It turned out that the smartest birds occupied much smaller territories in the woods. “Good problem-solvers can manage much more effectively in a smaller space – they can extract what they need more efficiently,” says Sheldon.
The project’s historical depth can also uncover secrets. The team can trace family trees of tits back 40 generations. “In human terms, that would be back to around the time of the Norman conquest,” Sheldon says.
That gives them access to detailed data from the decades before climate change was a significant factor, and so offers some of the best intelligence about how it can affect ecosystems. “We are seeing big changes in the annual life cycle. Key moments such as egg laying happen about two and a half weeks earlier now than in the 1970s,” says Sheldon, “but the birds are coping quite well.”
Sheldon sees the project running far into the future, but is excited by prospects in the shorter term. “Within 20 years the tags will get small enough, and smart enough, that we’ll be able to track entire populations in real time,” he says. Combining this with advances in genetic analysis and forest sensor technology, he says, “will enable us to understand many ecological processes at scales that right now we just can’t comprehend”.
While the technology in Wytham is racing ahead, you wouldn’t know it from walking through the woods. To them, 70 years is no time at all.
This article appeared in print under the headline “If you go down to the woods today…”
