Areas in the Wadden Sea where red knots, plump migratory birds, spend the winter are under pressure. The Wadden Sea is changing due to human influences such as gas mining, tourism and sea level rise. Researcher Selin Ersoy, an ecologist at the Royal Netherlands Institute for Maritime Research (NIOZ) studied how the “personalities” of individual red knots differ and affect how they forage. People who are fast explorers and take the risk of foraging in different areas also eat different foods. This could make the overall population of red knots much more resilient as their environment changes. Red knots could copy the foraging behavior of adventurous mates that succeed in new places. “Character differences between red knots seem to be an important ingredient for the resistance of the whole group,” said Ersoy. For the first time, her study shows that behavior that has been observed in experimental environments corresponds to actual behavioral strategies in real life in the wild, on the Wadden Sea marshes. This week, Selin Ersoy defended her PhD thesis at the University of Groningen.
Animals have personalities too
Red knots of all ages and sexes exhibit behavioral traits. These remain largely unchanged over time, but differ among individuals. Some individuals are more adventurous and exhibit more exploratory behavior in a new environment than others. Other individuals take fewer risks and hardly dare to move into a new environment. These “personalities” have ecological and evolutionary consequences, but to what extent is largely unknown, as few studies have investigated this in the field.
During her PhD research, Selin Ersoy developed a new way to identify personality variation between individual red knots. She wanted to know if behavior in experimental settings could be extrapolated to a larger and more complex natural setting and how individual differences develop.
“With our new method that allowed us to study the personality of animals in the wild, we found that red knots develop their personality, probably through the experience they get when they grow up,” says Ersoy. “After growing up, adults remain with exploratory behaviors. They seem to be like character types in humans.”
Explorers eat higher quality food
It was even possible for Ersoy and her colleagues to predict a suit of other behaviors in the wild. For example, variation in exploratory personality type (ie, slow vs. fast explorer) predicts foraging tactics and diet choice in the wild. Fast explorers use more visual foraging and eat soft prey such as shrimp or worms, while slow explorers use tactile foraging and feed on hard-shelled prey such as clams. This is a new explanation for variation in food niche specialization among individuals within the same population.
Exploratory behavior also refers to variation in movement across the landscape and over time. Ersoy: “We were amazed to see that the slow and fast explorers had distinctly different movement patterns during the night, while during the day they moved more or less the same. These different individuals even have different arrival times from migration. Fast explorers reach the Wadden Sea later than slower explorers.” Ersoy and her colleagues want to further study where they stay in the meantime. Perhaps these red knots need more time to care for their young in the Arctic.
The whole group benefits
“We found striking differences in feeding and movement patterns between slow- and fast-exploring red knots. This suggests that fast explorers could provide food information and new foraging opportunities for entire populations,” says Ersoy. “Such new opportunities are important as red knots face pressure from human impacts on their coastal wintering habitats, directly related to food availability. Rapid explorers can help entire populations cope with environmental change.”
The gap has closed between controlled experiments and the real Wadden Sea
The purpose of determining behavior in experimental setups is to understand the mechanisms behind behavior in the wild. Selin Ersoy’s study fills a critical gap between experimental research on wild animals in controlled environments and observed behavior in the wild.
“It’s a first step. We need to do similar research on personality in other animals and other natural habitats,” says Ersoy. “We want to know if personalities work the same way in other species and situations.”
Tracking the movements of guillemots with tiny transmitters
Researchers like Selin Ersoy track the birds using ultra-small radio transmitters placed on their backs during the summer months. The birds are not bothered by them. These transmitters send unique signals. These are received by antennas scattered throughout the Wadden Sea.
WATLAS is a new system that uses so-called “reverse GPS”. Tiny transmitters that are temporarily attached to birds transmit a signal of their own. This signal is received by fixed receiving stations in and around the Wadden Sea. Due to the small differences in signal arrival time between different receivers, the position of the animal-with-transmitter is calculated with an accuracy of a few meters, from second to second.
Thanks to WATLAS, researchers can track a migratory bird such as the red knot as it moves back and forth with high and low tide very precisely in search of food. Because many birds can be fitted with relatively inexpensive transmitters at the same time, researchers can now see interactions between different animals taking place from the comfort of their desk chairs.