Science

Surviving is a group effort

Heroic songbirds

By complete accident, RUG scientist Martijn Hammers discovered that the Seychelles warbler saves its own kind from certain death in the sticky seeds of a tree that catches birds. Does this mean that these birds might feel empathy, or are they ultimately only serving themselves?
By Simone Harmsen / Photo by Reyer Boxem / Translation by Sarah van Steenderen

Biologist Martijn Hammers discovered that Seychelles warblers on Cousin Island save each other from death at the risk of their own lives.

Birds that get covered in the seeds of the Pisonia tree can no longer fly and often die.

Hammers thinks that these rare songbirds display this seemingly selfless behaviour because they might get help in return in the future. Seychelles warblers live in groups and often work together.

In addition to these birds, only a few other social animals, such as dolphins and ants, are known to save each other from perilous situations.

Although some people say that this demonstrates that the birds have empathy, Hammers thinks there might be other explanations.

The behaviour could also be a reflex in order to stop the other bird’s cries for help.

Leestijd: 7 minutes (1,176 words)

Biologist Martijn Hammers researches the Seychelles warbler on Cousin, a small island off the coast of East Africa. During his research on the Seychelles island, he discovered that these small songbirds have a heroic streak. Risking their own lives, they save each other from the sticky seeds of the so-called birdcatcher tree, the Pisonia.

Cousin Island is rife with these trees. Birds that get caught in the seeds lose the ability to fly. They often end up dying. ‘Those seeds got into my hair once. If you try to pull them out, you pull out your hair with them’, says Hammers. ‘During my research on the island I saw a Seychelles warbler with seeds all over him, crying out for help. Another bird showed up and started picking the seeds off him.’ Once he was back in the lab, Hammers read in the database that a colleague had observed this behaviour once before.

Hammer’s and his colleague’s discovery is special because it shows that birds display a higher level of social behaviour than was previously thought. ‘Social behaviour comes in varying degrees, such as birds helping each other in rearing their young. But this behaviour seems to go even further. It is even more altruistic.’ Moreover, executing a rescue mission is rather complicated. First, a bird needs to recognise that the other bird is in trouble, identify the danger, and determine what it needs to do to help the other bird. That takes quite some insight. And, says Hammers, the heroic individuals run the risk of getting covered in the seeds themselves.

One good turn

He thinks that the rare birds save each other because it will benefit them in the long run. ‘That’s not as weird as it sounds’, Hammers explains. ‘These birds spend their entire lives in close-knit family groups. These groups work together on everything from rearing the young to defending the territory. It’s possible that one bird helping another does so in hopes of getting help from that bird in the future. It’s a logical explanation, whether the behaviour is a conscious choice or not.’

According to Hammers, however, the best explanation is that the birds are preserving their family group by rescuing others. When a bird saves a family member, the group retains its members, which enables procreation and territory defence. Hammers’ and his colleague’s discovery endorse this notion: in three of the four cases observed, the birds were family. In the fourth case, the bird was not family, but a helper who assisted in raising the young. Liberating their own appears to be effective: all the birds that were rescued lived for at least another six months. The Seychelles warbler lives for an average of six years – quite long for a bird, the researcher says.

Sensitive birds?

Some people say that the songbirds’ heroic behaviour shows that birds are capable of empathy. But Hammers says that conclusion is premature. ‘It’s possible that an animal, upon hearing a cry for help, has a reflex to stop that cry’, he says. ‘But’, he admits, ‘it’s highly likely that the birds are realising that the other animal is in danger and they need to save it.’

Behaviour like this is basically only ever observed in social animals. Hammers: ‘We’ve never observed this behaviour in sea birds on Cousin Island, even though sea birds get covered in the seeds much more often because they breed on the ground. The main difference is that sea birds are much less social. Familial ties and groups are much less important for these animals.’

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For example, we know that dolphins will save each other in perilous situations. But less intelligent and more unexpected animal species have also been observed behaving selflessly. ‘Ants have been shown to display social behaviour. They help each other when one ants falls into a pit’, says Hammers. ‘But they only do so for ants from their own colony. This shows that familial bonds are very important.’

According to Hammers, ants helping each other suggests that they are genetically programmed to help their peers. And the same might be true for birds. ‘It’s certainly tempting to think that birds possess empathy, but more research is needed before we can say anything for sure’, he concludes.

Three hundred

Hammers knows that the observed animals are family thanks to an enormous database with information about the birds. Scientists have been observing the three hundred Seychelles warblers on the island for 30 years. And that is pretty hard work.

Hammers: ‘We usually start between 6 and 7 in the morning, and we follow the birds around. We map territory and keep track of which birds help raise the brood. We also keep track of what the birds eat, and count the number of plants and insects in the territories.’ The researchers also capture and ring the birds. While they have them, they also take a small sample of blood. That way, they possess the genetic information of all the birds on the island.

Paradise

Cousin is a small island less than 700 metres long. It is part of the Seychelles, an archipelago north of Madagascar. ‘It’s the most beautiful tropical island. Before we had solar panels, we only had two hours of electricity a day from a generator. We have to get our drinking water in jerry cans from a neighbouring island. I have no real office, just a kitchen table with an ocean view. There are seven huts on the island. Some of them are inhabited by researchers all year round, and a few conservationists live on the island. But it’s basically a desert island.’

Yet the island was not always the beautiful nature reserve it is today. In the 1960s, the entire island was a coconut plantation. There were no more than 25 Seychelles warblers in the entire world. A nature conservation organisation bought the island and turned it into a reserve. The population recovered and the birds were translocated to four other islands in the archipelago.

Nowadays, tourists are allowed to visit Cousin Island. However, to protect the nature on the island, visits may last no longer than an hour. This makes the island a true paradise for sea birds, as well as for scientists: because the population of Seychelles warblers is so isolated there, Cousin Island is the perfect place to study them.

This is exactly what Hammers will be doing with the Veni grant he received from the Netherlands Organisation for Scientific Research. Discovering the Seychelles warblers’ heroic behaviour was a stroke of luck, but his actual research is concerned with ageing and social behaviour in the rare songbirds. That work will continue, albeit island-style: with his feet in the sand and the occasional encounter with a giant tortoise.

Nederlands

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