The last Tinbergen
Hundreds of birds from the great tits species in the Lauwersmeer area will become homeless this summer. This weekend, RUG biologist Joost Tinbergen removed the last nest boxes that were part of his research. They had been there for 22 years.
After 22 years, RUG animal behaviourist Joost Tinbergen is ending his research into a species of bird call the great tit in the Lauwersmeer area. The last of 600 nest boxes was returned to the Linnaeusborg this weekend.
Under Tinbergen’s guidance, 93,668 birds were caught and registered by students, PhD. candidates, post docs, and Tinbergen himself. Every bird is registered
Tinbergen mainly studied how the great tit population was regulated and the mechanisms that influenced natural selection.
The most remarkable result was that he was able to show that fitness had not only physiological aspects, but also social.
Parents with a large brood cannot handle competition as well in the following year. So whichever clutch size provides the largest offspring is not just dependent on the competition, but also on what the neighbours are doing.
His last PhD. candidate, Rienk Fokkema, will expand on this idea. For example, he would make nest boxes less attractive by making them shallow. The best nest boxes were occupied by parents who had small clutches the year previous. This means the fitness effect is long-lasting.
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It is going to be a difficult year for the great tits in the Lauwersmeer area. Less than two years ago, their beds were literally made. Spread out across the nature preserve, there were more than six hundred nest boxes: there were more boxes than tits. They had no idea that they were only there because of RUG biologist Joost Tinbergen’s scientific research.
The big clean-up
And this year? The birdhouses are gone. After 22 years, Tinbergen’s research into the relationship between fitness and brood size will end because the professor is retiring, and his last PhD. student Rienk Fokkema has finished his experiments. Last year, Fokkema had already reduced the number of boxes from 600 to 120 in order to research which birds were able to get the most popular nesting places. As soon as breeding season was over, the final large-scale clean-up was to take place. But nesting hornets – the largest wasp breed in the Netherlands at 3.5 centimetres – threw a spanner into those plans and a handful of boxes had to stay. This weekend, Tinbergen and Fokkema put the last boxes back into storage at the Linnaeusborg.
‘It’s not very nice to the animals’, Tinbergen admits. ‘They’ll come home one day to find their house missing.’ He explains that the birds will have to find natural shelters, like hollows in trees or holes created by woodpeckers. ‘When we reduced the number of nest boxes so drastically, we had a look to see what other places the birds had found to nest in. We even found a nest in the concrete base of a warning notice from the Department of Defence’, Fokkema adds.
But whether or not the chicks can survive nesting places like that remains to be seen. The life of a great tit is no bed of roses. Every year, only approximately 14 per cent of chicks survive, while a great tit lays an average of eight or nine eggs. No wonder they love the nest boxes so much; they protect them from predators.
Dirty Subaru
And yet Tinbergen made the choice to remove the boxes. ‘That was the deal we made with Staatsbosbeheer (the Dutch Forestry Service, ed.) back in the day’, he explains. Another reason is that the boxes require maintenance. ‘Every year, we have to loosen the screws or the tree will completely overgrow them. I could’ve chosen to keep checking the boxes, but I decided not to.’
The famous Tinbergens
Joost Tinbergens is not just any animal behaviourist. His departure from the RUG marks the end of a line of famous biologists from the Tinbergen family.
Joost is the nephew of the Leiden biologist Niko Tinbergen, who was awarded a Nobel Prize in 1973 for his research into how young birds fixate on their mothers. His father, Luuk Tinbergen, also left his mark on the field of ecology. He became a lecturer at the RUG in 1949 and was mainly interested in the population dynamics among tits and studied this in a range of forest environments.
Joost Tinbergen himself obtained his doctoral degree at the RUG in 1980 for his research into seagull foraging and became a professor in 2006.
There are even more famous Tinbergens. Nobel Prize winner and founder Jan Tinbergen is Joost’s uncle (and Niko’s brother). Joost’s brother is filmmaker Tijs Tinbergen, who made the revolutionary nature documentary Spreeuwenwerk in 1983, about Joost’s field research on Schiermonnikoog. In 2014 he also made Mees TV, about the families fascination with great tits.
That is no wonder. Under his guidance, more than 93,668 great tits were captured and studied by an endless stream of students, PhD. candidates, and post docs. All this data has been entered into an enormous database. For each bird, the researchers know who its parents are, how much it weighed at birth, how many brothers and sisters it has, and much more. ‘Every individual is registered’, says Tinbergen.
But that also meant that every year between late March and August he was out in the field doing measurements. Now, it’s time for something different: a spring vacation to the French Alps, for example. ‘He has been a little sentimental about it, though’, says Fokkema, gesturing toward his teacher as they drive a dirty, petrol-guzzling Subaru down the Strandweg to the military training area that houses the breeding grounds. ‘It’s going to take some getting used to.’
Marten
Suddenly, Tinbergen stops the car. ‘Remember, Rienk? That’s where we found that marten!’ he says, pointing.
That marten was a pine marten that showed up in 2011 and cost the researchers a quarter of the birds in the field. The animal was extraordinarily smart, because rather than try to fish the chicks out of the nest through the flight hole, he managed to lift the lids off the boxes. The researchers had to nail them shut to prevent all the chicks from dying. ‘It was very interesting, I have to say’, Fokkema goes on, ‘because until then, no natural predators had been spotted in the area. But this enabled us to study the effects of that.’
He is referring to an experiment where, over the course of two years, they made several nest boxes less deep by putting wood blocks inside. Fokkema wanted to see which birds managed to get the large boxes, and which one the shallower and therefore less safe ones. A great tit does not really stand a chance in a shallow box, but in a deeper one, if the bird is fit enough, it can get in all the way to the back and hope the marten misses it.
It turned out that birds who had raised a small brood and had therefore expended less energy raising their chicks clearly had a higher chance of getting a deeper box. In other words, their advantage was still in effect a year later.
Born in box 1649
The biologists, in the mean time, have spotted some tits. ‘There’s one’, Tinbergen points out. The binoculars come out. Both men study the bushes next to the road intently. ‘It’s ringed’, Fokkema sees. ‘It has a ring with a transponder.’
Later, back at the Linnaeusborg, Fokkema will identify the tit as AX.19224, born in box 1649 in plot 16 in June of 2013. She weighed 18 grams and was one of eight eggs, seven of which hatched. However, Fokkema reduced the nest to four chicks by putting three eggs into a different nest. On 6 May, she started brooding in box 1511 and on 17 December she was spotted asleep in box 1546.
It is one of the birds from the research into the fledging of young great tits. The transponder made sure they were registered as they left the box. A remarkable result: the order in which the birds fledge is unconnected to their chances of survival. The timing, however, is. ‘A bird that leaves the nest in the morning has the best chances, even when it does so on the second or third day,’ says Tinbergen. Why? That is not entirely clear just yet.
Game changer
The central theme to the years of research under Tinbergen’s management: how is the great tit population regulated and what are the mechanisms that influence natural selection? The most remarkable result, the game changer that Tinbergen is proudest of, is that through experiments, he has been able to show that fitness depends not just on physiological aspects, but that it also has a large social aspect.
‘A tit can lay a lot of eggs, or just a few’, he explains. ‘What is the best thing for her to do to ensure as much offspring as possible?’
Recent studies have shown an interesting disadvantages to having a large family. ‘Parents with many children have more difficulty facing the competition with other members of their species the following year. That means that whether clutch size actually provides the largest number of offspring depends not just on the competition around them, but also on what the neighbours are doing: whether they choose a large clutch size or not. The most important take away from this is that the social situation influences the clutch size the animal chooses.
Rare nest box
Fokkema expands on this idea in his doctoral research. He manipulated family size, removed nest boxes or made a selection of them undesirable right before breeding season by making them shallow. ‘Especially manipulating the attraction of a section of boxes is an elegant experiment’, says Tinbergen, ‘because although you’re watching all the birds, you’re still able to study the competition.’
However, last summer’s research, in which Fokkema drastically reduced the number of nest boxes before breeding season, showed no effect on parents with small families. Although: ‘It’s true we didn’t find that they had a bigger chance of getting a rare nest box, but we think that’s because the survival effect took place before March.’ In other words: these weaker parents may not have survived winter.
Young hornet
And then it’s time to remove those final boxes. Fokkema and Tinbergen walk the broad paths of the military training grounds for the last time. The wind is harsh and cold, but at least it stayed dry. ‘It’s never really all that bad’, says Tinbergen.
They leave the path when the dark green shape of a nest box becomes visible through the trees. They travel through the trees to get to it, navigating around some dead branches. Fokkema lifts the lid and Tinbergen takes out the remnants of the hornet’s nest. He pokes it with a knife and digs op the decaying remains of a dozen young hornets who never left the nest, even though the biologists so thoughtfully left the box intact.
Fokkema unscrews the final box from the tree and that’s that. The end of 22 years of Tinbergen’s research. Back to the Linnaeusborg.
The French Alps are calling.