According to a recently published study, if extreme temperatures continue, the southern yellow-billed hornbill will disappear in the warmer parts of its range by 2027.

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As climate change worsens, it brings increasingly extreme temperatures and longer and more frequent droughts. These factors are pushing more bird species beyond their ability to cope due to a myriad of effects or simply by being roasted alive (read more about these horrors here, here, here, here, here and here). An impending local extinction is that of the southern yellow-billed hornbill, Tockus leucomelas.

Southern yellow-billed hornbills are desert specialists

The southern yellow-billed hornbill is a medium-sized black and white spotted bird with a long black tail and a large, thick, down-curved yellow bill. These iconic birds are common and widespread residents across much of southern Africa, primarily in the dry scrub and forests of the Kalahari Desert. They feed on insects, spiders and scorpions as well as seeds they find on the ground. A socially monogamous species, they are well known for their unusual breeding and nesting habits where the female cements the entrance to her nest with mud and remains imprisoned there for 50 days. She leaves a narrow opening for her mate to feed her while she incubates her eggs and, later, her growing chicks. Because this nesting strategy is such an effective deterrent to predators, the breeding success of these birds depends primarily on the availability of food and, of course, rain.

In appearance, the southern yellow-billed hornbill closely resembles its sister species, the red-billed hornbill, Tockus erythrorhynchus — a species that was a major character in Disney’s 1994 animated feature, The Lion King. Zazu, as this dynamic avian character was named, was the royal advisor to Simba and his pride of lions, and was responsible for preserving order in the kingdom. Unfortunately, Zazu’s advice was rarely taken seriously.

What are the effects of climate change on decadal time scales?

“There is growing evidence of the negative effects of high temperatures on the behavior, physiology, reproduction and survival of various species of birds, mammals and reptiles around the world,” said the ecologist from conservation Nicholas Pattinson, graduate student at the University. from the FitzPatrick Institute of African Ornithology in Cape Town. Pattinson noted that heat-related mass mortalities that occur within days are increasingly being recorded, and pose a deeply concerning threat to population persistence and ecosystem functioning. But what happens to desert birds over periods of time longer than a few days?

“[T]The motivation for this study was to investigate whether rapid global warming has a demonstrable effect on the reproductive success of an arid zone bird over a longer time scale, and whether the sublethal “hidden” effects of high temperatures and drought could affect reproductive yields at the population level,” Pattinson told me by email.

For example, Pattinson and his collaborators studied the impact of climate change on the breeding success of the hornbill over a 10-year period. The southern yellow-billed hornbill is an ideal species for such studies because it breeds during the hottest time of year in the Kalahari Desert, and some of the links between temperature and its behavior and physiology are already quite clear. well understood. For example, we know that although hornbills never drink water, they are triggered to breed by rain.

The collapse of the hornbill population is imminent

Pattinson and collaborators studied a population of southern yellow-billed hornbills in the Kuruman River Reserve in South Africa’s Kalahari Desert between 2008 and 2019. They looked at long-term trends (2008-2019 ) breeding success as well as the success of individual breeding attempts. They also analyzed climate trends (1960-2000) for the region. The team then used this data to clarify the links between climate change and the breeding success of hornbills by modeling the relationships between rainfall and temperature, female entry into a nest cavity, and number of days that the female spent incarcerated in her nest after her chicks. hatched.

What they found was deeply disturbing.

When Pattinson and his collaborators compared the 2008-2011 breeding seasons to the 2016-2019 breeding seasons, they found that occupied nest boxes decreased from 52% to 12%, the chances of rearing and fledging successfully at least one chick decreased from 58% to 17% and the average number of chicks produced per breeding attempt decreased from 1.1 to 0.4.

Further, Mr. Pattinson and his associates have not recorded any successful breeding attempts when ambient air temperature reached or exceeded 35.7 °C (96.26 °F).

“During the monitoring period, the sublethal effects of high temperatures (including compromised foraging, provisioning and maintenance of body mass) reduced the chances of hornbills breeding successfully or even breeding at all. “, Mr. Pattinson explained in an e-mail.

Pattinson and his collaborators also found that overall livestock production plummeted even in drought-free years. This is because many desert-dwelling birds are forced to breed in response to rainfall, making it difficult for them to move breeding outside of the hottest times of the year when it coincides with the rainy season. , as is the case with hornbills.

But the birds in this study nested exclusively in wooden boxes, which tend to be warmer than natural tree cavities. Was it a problem?

No, Pattinson explained, because a significant part of the negative effects of high temperatures on breeding success and the likelihood of skipping breeding are felt outside the nest through the effects of extreme temperatures on foraging success. food for adult birds.

“Additionally, air temperatures at our study site are generally lower than those at the warmer margins of the southern yellow-billed hornbill’s range,” Pattinson added. “As a result, we suggest that these findings are still biologically significant and representative of the effects of high temperatures on hornbills in the warmer parts of their range.”

Rapid temperature increases kill birds before they can adapt

The rapid pace of climate change-induced temperature increases is happening faster than birds can adapt. Current warming predictions at the study site indicate that the hornbill’s threshold for successful breeding will be exceeded throughout the breeding season by 2027.

Thus, southern yellow-billed hornbills could be locally extinct in the warmest parts of their range as early as 2027. This loss would result from the fact that no young birds will survive to join the aging breeding population and due to changes massive amounts throughout the ecosystem that we all – birds and humans alike – depend on.

“Much of the public perception of the effects of the climate crisis is tied to calculated scenarios for 2050 and beyond. Yet the effects of the climate crisis are present and can manifest not just in our lifetime, but even in a single decade.

Source:

Nicholas B. Pattinson, Tanja MFN van de Ven, J. Finnie, Lisa J. Nupen, Andrew E. McKechnie and Susan J. Cunningham (2022). Collapse of breeding success in desert hornbills evident in a single decade, Frontiers in ecology and evolution: behavioral and evolutionary ecology 10:842264 | doi:10.3389/fevo.2022.842264

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