Bird Club learns more about Southern Yellow-billed Hornbills
Tanja van den Ven explained to members of the Polokwane Bird Club how the increase in global warming affects hornbills.
POLOKWANE -There are 10 species of hornbills in Southern Africa, and the Southern Yellow-billed Hornbills have a wide distribution range. In South Africa, you can find them in the northern regions of Limpopo, KwaZulu-Natal, North-West and the Northern Cape.
At a monthly meeting of the Polokwane Bird Club held before the lockdown, Tanja van den Ven introduced this interesting bird to the members: “There are two species in the Kalahari, namely the Southern Yellow-billed Hornbill and the African Grey Hornbill.”
She explained how the increase in global warming affects hornbills.
“These birds have a breeding system whereby they make use of natural cavities. The female goes inside, she plucks the whole from the inside while the male brings her mud and little pieces of insects. She can seal the opening and leave a tiny slit so that the male is responsible for the feeding of the female. She stays inside the nest for the duration of the incubation and also the upbringing of the chicks.”
The female, Tanja explained, will come out when the chicks are old enough to receive the food from the male. The female also undergoes a mould at this time which makes her very vulnerable. She loses all her primary and tail feathers. “The situation is very risky. About two months before breeding season, the male and female have to create a very strong bond as she will ask him for food and he will provide her with food. It takes about 30 days for her to regrow all her feathers.”
Temperatures in the nest box increase with both the chicks and the female inside. When the time is right, the female will break the seal and leave the nest. The idea is then for the chicks to reseal it but sometimes, the female will leave the nest too early. The chicks are too small to seal it again and this will result in a failed nest. Snakes and even mongoose can get into the nest.
“As long as the seal is intact, the birds are safe from predators in the nest. A failed nest can be caused by a combination of low food availability and high air temperatures. Females lay up to five eggs but not on the same day. If there is not enough food, she will eat the weaker chicks.”
Interesting facts about hornbills:
• Hornbills lose heat by panting and spreading their wings. They also reduce activity and shade seeking.
• Tanja weighed the birds and found that the bird loses 4,5% mass overnight and as the days get hotter, they lose more weight. While they pant, they cannot consume food.
• Hornbills do not drink water and source all their water from their food. As it gets hotter, they need more food but when it is hot, their prey hides.
• Hornbills only start breeding when the rain starts. They are monogamous and territorial.
• They use their beaks to lose heat into the environment. The blood vessels are situated very close to the surface of the bill and it is a way of passive heat loss.
• High temperatures affect male and females and the decisions they make, chick growth and the probability of a chick successfully fetching from the nest. In the Kalahari, hornbills might go extinct as they delay their breeding to a ‘cooler’ year which will not come.
