Climate Crisis Is Driving Cousins from Zazu, from the Lion King to Local Extinction

At the study site, southern yellow-billed hornbills. Credit: Nicholas Pattinson

The yellow-billed Hornbill, cousins to fan-favorite Zazu The Lion KingThe climate crisis is threatening local extinction. Between 2008-2019, researchers examined the effects drought and high temperatures on breeding success in southern yellow-billed hornbills living in the Kalahari Desert of Southern Africa. This is the first study to examine the effects of climate change on breeding success at the population level over a longer period of time.

The climate crisis is exacerbated by extreme climates such as high temperatures and drought periods that are frequent and intense in arid areas.

These animals are already suffering from the effects of climate change. Research has shown that warming climates can affect the breeding success of many bird species. They are breeding earlier and for shorter periods.

“There is rapidly growing evidence for the negative effects of high temperatures on the behavior, physiology, breeding, and survival of various bird, mammal, and reptile species around the world,” said first author Dr. Nicholas Pattinson, of the University of Cape Town.

“For example, heat-related mass die-off events over the period of a few days are increasingly being recorded, which no doubt pose a threat to population persistence and ecosystem function.”

Pattinson, along with his colleagues, investigated whether climate change has had an impact on the breeding success and survival of the southern Yellow-bill Hornbill, an Arid-Zone bird, over a 10 year period. The study was published in the journal Nature on May 19, 2022. Frontiers in Ecology and Evolution.

The yellow-billed Hornbill

The southern yellow-billed hornbill’s distribution includes most of southern Africa, with a large portion falling within the Kalahari Desert. It is believed that their numbers are decreasing.

The southern yellow-billed, monogamous species of hornbills is known for its unusual breeding and nesting strategy. They nest in cavities. The female seals herself inside the nest cavity and stays there for 50 days to care for the chicks and brood them. The male feeds the chicks and the female through a narrow vertical opening.

This type of nesting protects against predation. However, breeding success is dependent on other factors like climate and food availability. For example, yellow-billed Hornbills breed when it rains. This corresponds to the hottest days in the year. This makes it difficult to change breeding dates during the hottest times.

Population collapse

Pattinson’s team studied the population of southern yellow-billed Hornbills at Kuruman River Reserve, in the southern Kalahari Desert, South Africa between 2008 & 2019. Data was only collected from pairs of hornbills that were breeding in wooden nest boxes. They looked at breeding success at both broad and fine scales (long-term trends, individual breeding attempts) The team also examined climate trends in the region.

The monitoring period 2008-2019 showed that breeding output was reduced due to an increase in maximum air temperatures.

“During the monitoring period, sub-lethal effects of high temperatures (including compromised foraging, provisioning, and body mass maintenance) reduced the chance of hornbills breeding successfully or even breeding at all,” explained Pattinson.

Comparing the first three seasons of 2008 to 2011 to the last three seasons of 2016 to 2019, researchers found that the average nest occupancy fell from 52% – 12%, nest success (successfully raising or fledging at least one chicken) fell from 58% – 17%, and that the average number chicks per breeding attempt declined from 1,1 – 0.

No successful breeding attempts were recorded above the threshold air temperature of 35,7°C. There was a negative correlation between breeding output and days where the maximum temperature exceeded 35,7degC. This threshold is the point at which hornbills exhibit heat dissipation and normal breeding and nesting behaviors. These effects were even present in non-drought year.

Climate crisis rapidly approaching

The study shows how the climate crisis is accelerating is having adverse effects on charismatic species for alarmingly short times. Current warming predictions at the study site show that the hornbill’s threshold for successful breeding will be exceeded during the entire breeding season by approximately 2027.

“Much of the public perception of the effects of the climate crisis is related to scenarios calculated for 2050 and beyond,” Pattinson continued. “Yet the effects of the climate crisis are current and can manifest not just within our lifetime, but even over a single decade.”

“Despite no striking large die-off events, our prediction in this study is that southern yellow-billed hornbills could be extirpated from the hottest parts of their range as soon as 2027.”

“Sub-lethal consequences of high temperatures may drive local extinctions by resulting in recruitment failure (ie no young animals joining the population) and changes to the ecosystems on which we all depend.”

Reference: “Collapse of Breeding Success in Desert-Dwelling Hornbills Evident Within a Single Decade” by Nicholas B. Pattinson, Tanja M. F. N. van de Ven, Mike J. Finnie, Lisa J. Nupen, Andrew E. McKechnie and Susan J. Cunningham, 19 May 2022, Frontiers in Ecology and Evolution.
DOI: 10.3389/fevo.2022.842264