A recently published study shows that the southern yellow-billed Hornbill could become extinct in its hottest regions if extreme temperatures persist.
Climate change is causing more extreme temperatures and more frequent droughts as the climate changes worsens. These factors are causing more bird species to become unsustainable. The Tockus Leucomelas southern yellow-billed Hornbill is at risk of extinction.
Southern yellow-billed Hornbills are desert specialists
The southern yellow-billed Hornbill is a medium-sized, black-and-white speckled bird. It has a thick, yellow-colored bill and a long, black tail. These famous birds are common and widespread in southern Africa. They are found mainly in dry woodland and scrub in the Kalahari Desert. They eat insects, scorpions, and spiders, as well as seeds they find on the ground. They are monogamous and socially monogamous. Their unusual nesting and breeding habits make them well-known. The female seals her nest with mud, and she remains there for 50 days. As she broods eggs, and later her chicks, she leaves a small opening for her mate to pass food. This nesting strategy works well to deter predators. Breeding success for these birds is dependent on food availability and rain.
The southern yellow-billed Hornbill is very similar to its sister species, the Red-billed Hornbill, Tockus Erythrorhynchus – which was a key character in Disney’s animated feature-length movie The Lion King. This dynamic avian character, Zazu, was Simba’s royal advisor and charged with maintaining order in the kingdom. Unfortunately, Zazu’s suggestions were rarely taken seriously.
What are the impacts of climate change on decadal timescales?
Nicholas Pattinson is a conservation ecologist and a graduate student at the University of Cape Town’s FitzPatrick Institution of African Ornithology. “There is rapidly increasing evidence for the adverse effects of high temperatures upon the behaviour, physiology and breeding of various bird and mammal species around the globe,” said Nicholas Pattinson. He noted that heat-related mass deaths that happen in a matter of days are becoming more common. These can be a serious threat to the survival of species and ecosystem function. What happens to desert-dwelling birds if the time frame is longer than a few weeks?
“[T]he purpose of this study was to determine if rapid climate change was having an evident effect on the breeding success for an arid zone bird over a longer period of time, and whether sub-lethal effects of high temperatures or drought could be affecting population level breeding outputs,” Mr Pattinson explained to me via email.
So, over a period of 10 years, Pattinson and collaborators studied the effects of climate change on hornbill breeder success. Because it breeds in the Kalahari Desert’s hottest season, the southern yellow-billed Hornbill is a good species to study. Some of the relationships between temperature and its behavior are well known. We know for example that hornbills don’t drink water but are triggered by rain to reproduce.
The collapse of Hornbill populations is imminent
Between 2008 and 2019, Mr Pattinson, along with his collaborators, studied the population of southern yellow-billed Hornbills at South Africa’s Kuruman River Reserve. They looked at the long-term trends in breeding success (2008-2019), as well as individual breeding successes. The climate trends for the region (1960-2000) were also examined. These data were then used by the team to determine the relationship between climate change, breeding success, and hornbills. They also modelled the relationship between temperature and rainfall, female entry into nest cavities, and the length of time the female remained in the nest after hatching.
They found something deeply troubling.
His collaborators and Mr Pattinson compared the 2008-2011 and 2016-2019 breeding season to find that the number of occupied nest boxes dropped from 52% to 12 percent, that the odds of successfully raising and fleeging at least one chick fell from 58% and 17% respectively, and that the average number produced per breeding attempt declined from 1.1 to 0.
Furthermore, Mr Pattinson (and his collaborators) did not record any successful breed attempts when the ambient temperature reached or exceeded 35.7 degrees Celsius (96.26degreesF).
“During the monitoring period the sub-lethal effects on high temperatures (including compromised food, provisioning and body mass maintenance), reduced the chances of hornbills breeching successfully or even at all,” Mr Pattinson stated in an email.
His collaborators and Mr Pattinson also discovered that overall breeding output had declined even in years without drought. This is because desert-dwelling birds are forced to breed in response rain, making it difficult for them not to shift breeding to other times of the year, like it does for hornbills.
However, the birds in this study only used nested wood boxes. These tend to be warmer that natural tree cavities. This was a problem?
According to Mr Pattinson, this is because most of the adverse effects of high temperatures on breeding success, and the possibility of skipping breeding, are experienced outside the nest by the extreme temperature effects on adult birds’ foraging success.
“Moreover, the air temperature at our study site is generally lower than at Southern Yellow-billed Hornbill’s hottest margins,” Mr Pattinson said. These findings, however, are biologically significant and represent the effects of high temperatures upon hornbills in the hottest areas of their range.
Birds are dying before they can adapt to rapid temperature rises
Climate change-driven temperature rises are happening at a faster pace than birds can adapt. According to current warming predictions from the study site, the threshold for successful breeding in the hornbill will exceed by the end of the entire breeding season.
In the hottest areas of their range, the southern yellow-billed Hornbills may be extinct as soon as 2027. The reason for this loss is that no young birds will be able to join the aging breeding population, and the ecosystem itself has been drastically altered. This affects both birds and humans.
“Much of public perception about the effects of climate crisis is based on scenarios for 2050 and beyond. The climate crisis’ effects are real and can be felt not only in our lifetimes, but also over the course of a decade.