A masters student from the Nelson Mandela Metropolitan University’s (NMMU) marine apex predator research unit (Mapru) has played a pivotal role in aiding scientists to track wedge-tailed shearwaters known as “ghost birds”.
Danielle van den Heever, 24, who is studying towards a master’s degree in zoology, found a manner in which the “ghost bird” could be tracked by using a lightweight device that weighed 12 grams and was attached to the birds without harming them. Van den Heever adopted a nocturnal routine to study tropical “ghost birds”, which are slightly bigger than doves yet tough enough to fly hundreds of kilometres out to sea.
“Advances in technology have now led to lightweight tracking devices, weighing between eight and 12 grams, which can be attached to the shearwaters, enabling scientists to track them out at sea and this formed the crux of Van den Heever’s research,” the university said in a statement.
Van den Heever conducted her fieldwork at night when the animals returned to their underground-burrow nests after days at sea looking for food. She said she used special waterproof tape which was attached to a GPS, to the bird, in order to find out how deep and how long the birds dived underwater to catch fish.
“I used special waterproof tape to attach a GPS to the tail feathers of the birds,” Van den Heever said.
In her research, Van den Heever explained the patterns the birds would follow in order to go look for food.
“They would generally stay away for one or two days but some spent up to 18 days at sea. Sometimes both parents would go out to sea, leaving their chicks alone in the nest, sometimes for a very long time. But the chicks were safe from most predators in the underground burrows.”
Van den Heever’s research is among the first in the world as it was first adopted in the Seychelles.
“It was the first time these high-tech tracking devices had been fitted onto the shearwaters at Reunion and only the second time at the Seychelles,” NMMU said.
“From the Reunion data, she found that some of the birds flew as far as Madagascar, some 800km west of Reunion. These long trips were to a very productive area (rich with fish), that is also favoured by boobies, terns and other tropical sea-birds.”
“At other times, they would visit a few spots just south-east of the island, these were up-welling areas where nutrients are pushed up from the bottom of the sea on the sea shelf, where there was lots of food available,” Van den Heever said.
Van den Heever said her research in identifying the birds’ feeding hot spots would “hopefully contribute towards recommendations for the allocation of potential marine protected areas in that area”.
She said there was conflict between the shearwaters and the commercial tuna fisheries on the two islands.
“These birds don’t feed on the tuna but the tuna drives up the fish they can eat. With widespread tuna fishing, however, there is less food being driven to the surface for the shearwaters.”
She noted that the birds were also affected by rising sea levels as a result of climate change.
“This influences where they can nest. What I found at the Seychelles is that during super moons, when tides are unusually high, the nests, which are burrows in the sand near the high-water mark, are washed away. Sometimes you would see eggs floating away.
Reunion was not as affected as the birds tended to nest in cliffs, burrowing in rock holes.”
She also conducted a census in the Seychelles, looking into more than 700 burrows using an endoscope (a flexible tube with an attached camera), attached to a laptop. Globally, there are more than five million wedge-tailed shearwaters but research has shown that their numbers are dropping for several reasons, among them invasive species and over-fishing, hence the need to monitor their behaviour at sea and protect their feeding grounds. Senior zoology lecturer at NMMU and Mapru head Dr Pierre Pistorius supervised Van den Heever’s research and said she had been passionate about marine life since she was a little girl.
“She saved up her money at age 11 to pay for a scuba diving course, which sealed her decision to pursue oceanfocused work,” Pistorius said.