The powerful impacts of climate breakdown are already being felt by the natural world, driving many species towards extinction.
In The End of Eden, journalist and naturalist ADAM WELZ invites readers to meet wild species on their own terms in a range of ecosystems that span the globe as they struggle to survive. Read on for an extract.
Energy, Water & Time
Scientists have been closely observing Southern Yellow-billed Hornbills in a Kalahari study area since 2008. They’ve erected about 40 hornbill nest boxes in the study area, substitutes for the natural tree cavities, to standardise nesting conditions
and make nest monitoring easier.
Their research is producing remarkable – and shocking – results. In the 10 years between 2008 and 2019, hornbill breeding success collapsed. Nestbox occupancy went down from 52 per cent to 12 per cent, success of the nests that were occupied from 58 per cent to 17 per cent, and the average number of fledglings produced per breeding attempt from 1.1 to 0.4. In short, the birds have gone from breeding at a decent rate in 2008 to producing almost no young in the early 2020s.
Why the stunningly rapid collapse? Once the female of the hornbill pair is cemented into the nest hole, the male needs to spend almost all of his day finding and transporting food for them both. Finding food is labour- and time-intensive work! But he must also constantly manage his internal thermal energy budget. When the sun comes up, he’s immediately impacted by its rays, a significant source of radiant energy, much of which is absorbed by his body surface and becomes thermal energy inside him. He receives radiant energy not only directly from the sun but also indirectly from all the surfaces around him; it reflects toward him off the sand, off the grass and leaves, and off the base of any clouds that might be floating above.
The more he moves his muscles to fly and hop in search of food, the more he transforms chemical potential energy into thermal energy inside his body. When he stands on the ground, energy passes into his feet by conduction from the hot sand, and the sand, of course, is also generating masses of high-temperature air, which rise up against him and transfer more thermal energy into him.
He can reduce the amount of energy passing into his body by staying in the shade; this cuts off most of the direct radiant energy from the sun. He can also stay still and not use his muscles, thus damping down an important internal source of thermal energy. But changing where he sits and what he does changes very little about his exposure to the thermal energy in the air. As the day unfolds, the air temperature rises, and when it rises above his body temperature, then thermal energy naturally, passively, begins to move from the air into his body by conduction.
When the male Yellow-bill’s internal thermal energy starts to reach dangerously high levels, his last option for keeping his body temperature within limits is evaporation. He can actively transfer energy out of his body by turning liquid water into water vapor on the inside surface of his mouth, and he does this by panting.
The higher the daytime air temperature soars and the longer it remains high, the longer he must sit in the shade and pant, and the less time he has available to find food for himself, his mate, and their young. Hornbill researchers found that males were likely to engage in ‘heat dissipation behaviour’ when the air temperature went above 34.5 degrees Celsius (94.1°F), and that Hornbill breeding performance decreased in proportion to the number of days where the temperature exceeded 34.5 degrees Celsius. They also found that if the average maximum temperature during the breeding attempt was greater than 35.7 degrees Celsius (96.3°F), then no young survived.
Average maximum daytime temperatures have been rising in the Kalahari. Nowadays a male Hornbill simply doesn’t have enough foraging time in the day to keep his walled-in female well fed. When the young hatch and she can break out of the cavity to help him out, she faces the same temperature-management problem. Even with both adults working together, they don’t have enough active hours in the day to find enough food for their babies. Climate predictions for the hornbill study area are that daytime maximum temperatures will exceed 35.7 degrees Celsius for every day of the breeding season by 2027: it will then be impossible for the birds to produce young, and the species will die out from the region.
The impact of the slightly higher average daytime air temperatures now being experienced in many arid areas is not dramatic and immediately noticeable. Birds don’t fall out of the sky en masse. They just fail to reproduce and quietly fade away. Yellow-billed Hornbills can live for up to 10 years, so it might be a long time before the absence of adults is noticed and their role in the ecosystem is no longer filled, but their species is just as surely doomed in the Kalahari as if a colossal heat wave, a week of 20 degrees above normal, were to kill them suddenly. All around the world, bird species are vanishing from hot, dry areas where they were recently common. Avian vacuums are forming in the hearts of arid zones.
ABOUT THE AUTHOR
Adam Welz is a South African writer, nature conservation consultant, photographer and filmmaker.
Welz was born and raised in Pretoria, South Africa, and has lived, worked and travelled on six continents, including extended periods in the United States. He consults on conservation projects and is an experienced birder and keen all-round naturalist.
His writing focuses on wildlife, nature conservation and climate change, and has appeared in numerous publications worldwide including The Guardian, The Atlantic and Yale Environment 360. He’s directed, shot, researched and scripted a number of movies (mostly documentaries) and is seldom far from a stills camera or two. He lives in Cape Town with his wife, Sarah, and their rambunctious triplet daughters.