University of Pretoria (UP) researchers have become the first to document a disturbing new threat to the endangered grey-headed albatross: wind-driven, land-based deaths. The team documented the phenomenon on remote Marion Island during the sub-Antarctic summer. The study, published in the journal Marine Ecology Progress Series (MEPS), sheds light on the growing risks that extreme weather pose to vulnerable wildlife.

As home to the second-largest breeding population of these seabirds, the island is important to the long-term survival of grey-headed albatrosses, of which only 250 000 are left worldwide.

While albatrosses are built for speed and soaring on ocean winds, they’re not as agile when flying over land in extremely windy conditions. This can cause some to crash-land, with fatal consequences, says Dr Janine Schoombie, an aeronautical engineer who holds a PhD in Mechanical Engineering from UP. She investigated the precise aerodynamics behind the unparalleled efficiency in flight of the grey-headed albatross.

“Grey-headed albatrosses have wingspans of 2,2 metres, and specialise in gliding, not flapping,” Dr Schoombie explains. “Their long, narrow wing shape is adapted for low-cost dynamic soaring flight, similar to that of glider aircraft. However, the same adaptations that make them super gliders also make their wings less manoeuvrable. Flying over land becomes riskier, particularly when they take off or land.”

Marion Island study 

On Marion Island, two densely packed nesting sites are situated along cliffs some 50 to 200m above ground. In 2017, South African researchers and MEPS co-authors Chris Jones and Michelle Risi observed the carcasses of many grey-headed albatrosses in the inhospitable Santa Rosa Valley, close to one of these colonies. The broken bones of these birds provided stark evidence that they had fatally crash-landed.

Detailed carcass surveys followed from October 2017 to June 2021. This included surveys by Dr Schoombie and her husband, zoologist and UP alumnus Dr Stefan Schoombie, when they were members of the 2019 annual South African research team to Marion Island.

“We were shocked to find so many carcasses,” Dr Schoombie recalls. “Some were very old, which showed that fatal crashes may have been part of the birds’ life on the island for many years.”

Four years’ worth of surveys found that at least 41 adults and 40 fledglings on average died every year after crashing into the valley.

“For this particular colony, it’s worth about 2% of its annual production of fledglings, 0.5% of its estimated annual breeding adult population and an estimated 11% of annual deaths among adults,” Dr Schoombie says. “This might seem like a low number, but remember that grey-headed albatrosses can live up to 40 years, and that these seabirds usually enjoy a very high survival rate. Even a small increase in annual adult deaths could influence their population growth.”

Other researchers recently noted an increase in strong northerly winds experienced on Marion Island. They attributed it to a poleward shift in western winds (the so-called Southern Ocean Westerlies) over the Southern Ocean.

“If this trend continues, it’s likely that grey-headed albatrosses breeding on the ridge will more regularly have to depart their nests in unfavourable conditions,” Dr Schoombie says. “Continued surveys are required to monitor the effect that changes in wind conditions and the likelihood of more crashes could have on bird numbers over the long term.”

The influence of winds

Months of observing the albatrosses in flight have shown that at some point, most breeding adults fly over the “crash hotspot” situated below the centre of the particular colony. Wind conditions likely cause the crash-landings. Most occur when adults leave the colony for the sea to forage to feed their chick and when they fly low for about 2km over a particularly rugged valley in strong variable westerly or north-westerly winds and downdrafts. Dr Schoombie found that wind variability, together with the presence of downdrafts, may cause birds flying low over the valley to experience a sudden loss of lift, thus losing altitude and crash-landing.

“Departing albatrosses tend to lose altitude immediately after take-off, in contrast to returning birds typically arriving at higher altitudes,” she explains. “If uninjured after crash-landing, the heavy birds cannot take off again from the sheltered valley because there is not enough wind to help lift them off.” 

Why do the birds not wait for more favourable conditions before flying off the island?

“Adults returning from the sea to relieve partners from incubation or brooding duties, or to feed larger chicks, have the option to wait offshore until conditions for landing at the colony fall within acceptable limits,” Dr Schoombie says. “However, once relieved of guarding their chick, the adult that remained on land may be too hungry to wait any longer before flying off.”

Wind tunnel work

“As an aeronautical engineering student, I assumed I’d find detailed aerodynamic information in literature, or that there would at least be a detailed geometry of the most famous of all albatrosses, the wandering albatross,” Dr Schoombie says. “When I could not find enough detail to answer my questions, I challenged myself to fill this knowledge gap.”

As part of ongoing investigations into albatross crash-landings, she uses UP’s wind tunnel facility to conduct experiments on the aerodynamic forces acting on the birds’ wings during flight, using three grey-headed albatross wings donated by the Fitzpatrick Institute of African Ornithology based at the University of Cape Town. The digital design of the wing and body of a grey-headed albatross was published in the journal Bioinspiration & Biomimetics.

“It’s much easier to determine the aerodynamics of an aeroplane’s rigid wing than that of birds,” Dr Schoombie says. “Aspects like its build and feathers, along with the way that wings bend at different wind speeds, all influence the aerodynamic loads.”

As wind patterns shift, this research highlights the need for continued monitoring and targeted conservation efforts.

Read more about how UP researchers are finding ways to make air travel cheaper, faster and cleaner by studying the flight of the albatross for inspiration on Page 6 of RE.SEARCH 2: Innovation.

Read more about how climate change is shifting wind patterns on Page 10 of RE.SEARCH 4: Transdisciplinary