Tree-climbing (at 74) is for the birds

WHEN  white-backed vultures pair up and build nests in the camelthorn tree crowns overlooking the Kalahari grasslands in April; as the down feathers of the chicks, which must be ringed in October, make way for pin feathers in August; then a tenacious grey-headed man climbs the trees to study the birds with his blue eyes.

Next to the tree stands his long ladder, and on the ground his 19-year-old blue Hyundai bakkie with a folding table, equipment and research notes.

He is the 74-year-old ornithologist Angus Anthony, who primarily works at De Beers' Dronfield Nature Reserve just outside Kimberley. He is usually either up in the tree at the vulture nests, protected by thick, long gloves against the thorns, or on the ground ringing chicks and making notes. A pair of binoculars, a camera with a long lens, GPS equipment and files filled with information are within reach.

His more than 30 years of research, primarily on white-backed vultures — a self-imposed lifelong calling — earned him a medal from BirdLife South Africa last year.

Three times a year, Anthony undertakes the 736km journey from his home in George to Kimberley to collect data and record observations. In addition, he covers more than 450km in the veld, driving in a grid pattern among camelthorn trees at Dronfield, tracking vulture nests.

This year, he drove just as many kilometres on other reserves and farms such as Benfontein, south of Kimberley, Samaria to the east, Inglewood to the north, and the Waterkolk section of the Rooipoort Game Reserve, 60km south of the city, tracking vulture nests. Of the 280 he observed, 200 were active.

“It is heartening that the number of active breeding pairs and nests in the area has grown over the past five years. We would like to determine the reasons for this," he says.

“In July and August, the camelthorn trees shed their leaves due to the cold and windy conditions, a perfect time to find nests in the treetops and mark the trees as active. In October, the chicks are ringed and wing markers are attached, they are weighed and their wings are measured. In April, the vultures build their nests, pair up, and lay eggs until the beginning of May. The incubation period is 56 days."

Threats to vultures

On the first Saturday morning in September, International Vulture Awareness Day, Anthony stands at the starting point where athletes from the Kimberley Harriers running club are about to participate in the seventh Vulture Trail Run in Dronfield. He tells them about the role of these birds in the ecosystem and what threatens their survival. This includes intentional and unintentional poisoning by farmers and poachers, lead poisoning when they feed on carcasses shot with lead ammunition, collisions with structures, electric shocks from power lines, drowning in farm dams, habitat and food source loss, climate change, muti (traditional medicine) trade and other human activities.

He asks the athletes to inhale the fresh air, observe the gemsbok and other wildlife and look up in the sky. Vultures are known for their excellent eyesight, which allows them to spot carcasses over several kilometres. They play a key role in the ecosystem by cleaning up the environment when they feed on rotting carcasses, helping to combat the spread of dangerous diseases and bacteria, while also recycling nutrients into the environment.

Vultures are an ecologically vital group of birds whose survival is under threat. Anthony contributes to changing that.

He knows the reserve like the back of his hand and marks the coordinates of each nest tree on his GPS device as he traverses the veld. Anthony retired from his role as a farm manager 19 years ago after caring for the large cattle herd on Dronfield and other De Beers farms for 17 years. The farms were later converted into a game reserve, and the company fully supports the research.

While the athletes run in the veld, the vultures survey the area from the power lines where they perch. They await warmer winds to lift them into the upper air currents.

Ringed and measured

At camelthorn tree number 578, Anthony stands atop his ladder and carefully removes the chick from its nest. The adult vulture, which has been caring for the chick and protecting it from the cold spring air, perches on a power line, observing him from a safe distance. Down feathers and fresh vulture dung on and around the tree in winter (when it doesn't rain) are a good indication that there is an egg or chick in the nest.

Last October, Ester van der Westhuizen-Coetzer, the conservation manager of the Ekapa mining company, assisted in removing and returning chicks from the nests as a volunteer. At other times, it's Julius Koen and Eddie MacFarlane who help. Most chicks are 90 days or older and have fully grown wings, ready to start flying within two weeks. Their right legs are thick enough for a ring with a Safring identification number.

Before setting up the ladder, Anthony circles the tree to determine which branch is strong enough to bear the ladder's weight. He climbs up with his sturdy rubber bag and attaches the rope to a branch. Unnecessary branches are trimmed to allow him to reach over the nest with his body. He places the chick headfirst into the bag and lowers it down. Van der Westhuizen-Coetzer sets up a table and lays out the equipment. Anthony descends to record the chick's details with her.

With the chick's head still in the dark bag to reduce stress, it is weighed. The weight is an indicator of its health. The right leg is ringed, with the numbers facing upward for birdwatchers to identify the bird later. The right wing is extended and measured, providing an accurate indication of its age.

“While the chicks' wing lengths were usually just over 400mm, we've had four or five small chicks in recent days with a wing length of 50mm. These chicks likely come from second nesting attempts."

A wing length of 400mm indicates the chick is 77 days old, with a five-day margin of error. Chicks typically start flying at an average of 125 days old with a wing length of 600mm, which is close to the adult measurement.

The researchers place plastic wing markers on both wings in locations that won't irritate the chick. These markers rotate freely, allowing the vulture to preen its feathers. Then, Anthony climbs back up to return the chick to the nest.

The rings and wing markers help determine the extent of white-backed vultures' distribution in southern Africa. Kimberley, Mokala National Park and surrounding areas are the southernmost regions where white-backed vultures breed in Africa.

“The markers deteriorate after about seven or eight years and fall off," says Anthony. “Many adult birds cannot be identified at a distance with wing markers, or it's difficult because they have only one marker left. It would be beneficial if markers could be placed on adult free-flying birds with the necessary permissions to determine if they return to the same nests and keep the same breeding partners. Catching them is very difficult. In April, I tried to lure them with carcasses, but they didn't feed on them."

April would also be the ideal time to observe breeding pairs together when both are involved in nest-building. “I could see if the breeding pair is ringed and marked. Now it's too difficult because one of the pair is always with the chick at the nest, and the other one is out looking for food. I would have to spend days at one nest to see both birds when they exchange duties."

Reuse of nests

Anthony also checks if nests from the previous year have been reused. If he finds wing markers or metal rings around the tree, it indicates that the chick from the previous year perished. Only 50% of chicks eventually become mature enough to breed.

“We can see failed breeding attempts when the nest is lined with grass but empty, or when there are remains or eggshells deeper in the nest material. Sometimes the parents lay another egg, but the survival of these chicks that hatch later than the others is less successful. In other cases, the nest is built but for unknown reasons the vultures do not lay an egg."

Unlike other raptor species, such as eagles, the sex of vultures cannot be determined by physical characteristics such as body size, head shape or feather colour; it can only be determined with blood samples.

To collect data from the active trees, Anthony gathers bones from carcasses, eggshells and feathers, which he seals in a plastic bag and marks with an identification number. The number corresponds to the metal tag with which the trees are marked for identification. Over the past three decades, more than 650 trees in Dronfield have been used by white-backed vultures as breeding sites.

“The membrane in the eggshell from which the chick hatched can be used in tests to indicate if the birds are contaminated with a pesticide. The birds can also ingest toe bones from a carcass to obtain calcium from them, and other bones are eaten for the nutritious marrow inside."

In the past five years, Anthony has collected more than 300 feathers. “These can be analysed with a spectrogram test to determine their chemical composition. The feathers are burned under laboratory conditions, and the colour of the flame is an indication of the vulture's diet content. These tests have been conducted in Israel. They show what the chemical composition is in the feathers, how it varies in different vulture colonies, and therefore, their diet as well."

Analyses and permits

Anthony says he hasn't been able to find an expert at a university to analyse the feathers. Additionally, special permits are required to collect feathers and move them between provinces.

The results could potentially indicate whether the same vultures return to Dronfield annually and if vultures from elsewhere also arrive. In Dronfield, the number of breeding pairs has increased from 55 to 110 over the past 30 years. At Waterkolk, there were 27 breeding pairs this year, whereas there were none five years ago. On Benfontein, the number of breeding pairs has increased from 27 in 2018 to 33 this year.

Another puzzling question is why some nests are used only once. “Could it be that the birds have died, lost interest in breeding, or gone elsewhere?"

According to Anthony's information, 17 new nests are built in Dronfield each year, and some nests have been used up to 25 times over 31 years. Trees with nests also burn in veld fires. One such tree partially regrew, and the nest on it is considerably smaller but still in use. This is where he took a picture of a chick. “The little one bit me and brought up its breakfast." Vultures' stomach acid with a pH of 1 is much stronger than that of a human.

In the 1970s, Anthony conducted research on black vultures in Zimbabwe under the mentorship of Prof Peter Mundy. Broad-winged eagles, African fish eagles and other eagles were also studied. In 1983, he left Zimbabwe. Ten years later, he began studying white-backed vultures, as well as eagles, secretary birds and giant eagle owls, in Dronfield.

“The breeding pattern of white-backed vultures in Dronfield has been studied since the 1960s when researchers studying raptors accidentally stumbled upon the nests. Mark Anderson, at that time the ornithologist for the Northern Cape Department of Nature Conservation and currently the CEO of BirdLife South Africa, still leads the research."

Lead poisoning

In recent years, Anthony has also assisted Linda van den Heever of BirdLife SA in taking blood samples from chicks for her research project on lead poisoning in vultures.

The Hawk Conservancy in England largely funds Anthony's expenses, while the Puy de Fou Raptor Centre in France also contributes. Members of both organisations have been visiting for several years to help him in the veld.

The researchers also aim to determine which factors contribute to vulture mortality.

In 2022, 54 chicks were raised at Dronfield, a success rate of 46%. In total, 64 breeding attempts by parent pairs mostly failed during the egg phase. In five nests, the remains of dead chicks were found.

The weakest breeding season was in 2012 with a success rate of 33%. Out of 76 active nests, only 25 chicks were raised. In total, 51 nests failed during the egg phase, and 15 chicks died.

Anthony believes there are many places in sparsely populated countries such as Namibia and Botswana where vultures breed without people being aware of it. “I know of a farmer in Zambia who has counted 1,500 vultures at a vulture restaurant, of which only one had wing markers. Our research on vulture numbers is critically important. In India and Pakistan, they lost about 40 million vultures in 10 years before they realised it. It took five years to determine that the cause of the deaths was due to diclofenac, an ingredient in livestock medicines. Hindus, who do not eat beef, were putting out the carcasses for the vultures."

He also hopes South African research on lead poisoning can contribute to greater awareness of all critically endangered vulture species and that corrective measures will be taken in time to prevent extinction.

“I still have so many questions, despite textbooks. For example, is it true that a vulture pair stays together for life?"

♦ VWB ♦

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