Biology How Southern Ground-Hornbills Keep Their Cool

BIOLOGY climate change. In the 1970s Alan and Meg Kemp’s pioneering research on the ecology of this species in the Kruger National Park revealed that ground- hornbills are, compared to many other species, relatively heat-intolerant and retreat to shade and begin panting at comparatively mild air temperatures. These observations, together with recent evidence that hot weather nega- tively impacts the physical condition and breeding success of many birds in subtle but nevertheless consequential ways, provided the stimulus for several recent and ongoing projects aimed at in Mpumalanga. By taking thermal The combined capacity of the ground- understanding how ground-hornbills images of the birds over a range of air hornbill’s beak and bare skin to radiate are likely to fare under hotter future temperatures from 11 to more than 35 heat is impressive, reaching approxi- conditions. degrees Celsius, Andries was able to mately six watts at an air temperature In a new paper in Journal of Avian visualise how the temperature of the of 26 degrees. This mechanism gives Biology, researchers from the Univer- beak surface changes and to quantify the bird the capacity to dissipate about sity of Pretoria and the Mabula Ground the associated heat losses. three-quarters of its resting metabolic Hornbill Project (MGHP) teamed up The surface of the ground-hornbills’ heat production simply by adjusting to further investigate the physiology of beaks warmed sharply as soon as the air the circulation of blood through ca- BirdLife South Africa’s Bird of the Year temperature exceeded 20 degrees, con- pillary beds in the beak and under the 2020. Over the past decade, research firming that they actively govern blood skin on its face and throat. on groups as diverse as toucans, horn- flow to the beak and use it as a control- The findings of this study raise the bills and Darwin’s finches has revealed lable heat radiator. By raising the tem- possibility that the heat-loss capacity that the avian beak is a sophisticated, perature of the beak to as much as 10 to provided by the beak and bare skin is controllable heat radiator. During hot 12 degrees above that of the surround- one of the reasons why the Southern weather, these birds all direct blood to ing air, the birds used this structure to Ground-Hornbill’s distribution can capillary networks in the beak, caus- help dissipate excess body heat. The ob- include some of the hottest parts of ing its surface to warm and lose heat servation that ground-hornbills begin southern Africa. to the surroundings. Heat loss via the this process, which is invisible to the During the Kemps’ research in the HOT beak does not require the evaporation naked eye, at such low air temperatures Kruger National Park, when air tem- of water. For this reason it may be par- is consistent with the observations of peratures neared 35 degrees they oc- ticularly important for desert birds for them beginning to pant in the mid-20 casionally observed fluid in the groove whom water conservation is vital, as degrees, retreating to shade at about 30 in front of each nostril along the length well as for birds that inhabit very hu- degrees and generally showing signs of of the birds’ beak. Andries also docu- f lushes mid habitats in which evaporation is heat stress during hot weather. mented this and noticed birds some- impeded. It may also perhaps be signif- Impressive as the heat loss from the times wiping their beaks on their MARIETJIE FRONEMAN icant in non-drinking species like the ground-hornbills’ beaks may be, this plumage, apparently to spread the fluid How Southern Ground-Hornbills keep their cool ground-hornbills. turned out to be only part of the sto- over a larger area. Areas of the beak wet To establish whether Southern ry. Andries also measured the surface in this manner were evident as promi- above Footage obtained with a thermal- ew sounds are more evoca- birds of the savannas and woodlands Ground-Hornbills use their beaks as temperatures of the bare skin on the nent cool spots in thermal images, imaging camera provides insights into how tive than the booming duets of of southern and East Africa has, how- heat radiators, University of Preto- birds’ face and throat. He found evi- suggesting a function of speeding up ground-hornbills regulate blood flow to Southern Ground-Hornbills, es - ever, declined sharply in recent decades ria BSc (Hons) student Andries Janse dence that blood flow to these regions heat loss through rapid evaporation. At unfeathered areas. Fpecially when they accompany the because of habitat loss, poisoning and van Vuuren used a high-end thermal- is also regulated in such a way as to aid these high air temperatures there is no last few whoops of hyaenas, distant other human impacts. As a result, the imaging camera to measure surface heat dissipation. By maintaining large, longer a large temperature gradient for opposite The beak and unfeathered skin lions’ roars, deep hoots of a Verreaux’s species is now red-listed as Vulnerable temperatures of ground-hornbills at approximately constant differences passive heat loss between the beak and play a hitherto unappreciated role in helping Eagle-Owl and the sawing cough of a globally and Endangered in South Af- the National Zoological Garden in between skin temperature and air surrounding air, which is probably why Southern Ground-Hornbills to keep cool. prowling leopard in the half-darkness rica, Swaziland and Namibia. Pretoria and the MGHP’s new Baobab temperature during warm conditions, the birds keep this behaviour in reserve just before dawn breaks over the Af- Another significant threat looming Specialised Conservation Rearing Fa- these areas add significantly to the rate until it is really hot. rican bush. The number of these stately over the Southern Ground-Hornbill is cility at Loskop Dam Nature Reserve at which heat is dissipated. ANDREW McKECHNIE & LUCY KEMP 52 AFRICAN BIRDLIFE JULY/AUGUST 2020 SOUTHERN GROUND-HORNBILL 53.

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