Stories from South Africa: Southern Yellow-Billed Hornbills

A whole new soundscape

For the first few days in South Africa, I stayed at my friends’ home in one of the reserves that make up Kruger National Park. Lee and Kersey’s home and watering hole is pure magic on the Parsons Reserve: surrounded by wild landscape, and regularly visited by lions, hyena, elephant, leopard, vervet monkeys, and other creatures… who, of course, leave their tracks on the fine sand of the local trails.

Of course the sights of the bush are foreign to a child of the Northern Hemisphere forests, from the prickly knobthorn. buffalothorn, and sicklebush trees, to the array of native animals, to the very stars overhead at night. The sounds, too, are new and strange. At night, hyenas call with a distinctive swooping whoop, while lions groan and grunt to signal their movements. By day, a new world symphony from a feathered orchestra fills the air, with percussive punctuations from elephants crunching cambium off branches of marula and spikethorn.

One morning, I woke to odd cries outside my friend’s home in Kruger National Park: a series of repeated, almost stutter-y “AWK”s. (Listen to a similar recording here.) Puzzled, I peered out the window and saw this pair of striking black-and-white birds with massive curved bills, perched in a tree, speaking to one another.

Southern Yellow-Billed Hornbills

This was my first sighting of Southern yellow-billed hornbills (Tockus leucomelas), a common sight around the Greater Kruger area of South Africa. These medium-sized birds are distinctive for their long, curved bill, their powerful, controlled gliding from branch to ground, and their significant time spent walking about on the ground. I often observed yellow-billed hornbills turning over leaves and flipping up sand with those magnificent beaks, foraging for the invertebrates that are the mainstay of their diet. Although this was the only hornbill species I observed, there are several hornbill species present here in winter, including the Southern yellow-billed hornbill, Southern red-billed hornbill (with a slightly higher pitched call), and the much larger Southern ground hornbill (with its banjo-string vocalizations).

To visualize hornbill tracks, imagine a bird track a kindergartner might draw, with toe 1 facing back and toes 2-4 facing forward. This is a “classic bird track” structure, or anisodactyl. Now, modify this shape by fusing the first part of toes 3 and 4 (the outer, forward-facing toes). This is a syndactyl foot structure, shared by hornbills and kingfishers.

Their tracks are very distinctive: the shape of a bent banana, about 6 cm in length. We often found walking trails, as well as paired tracks where the hornbill had taken off.

Interconnections: Southern yellow-billed hornbill and Dwarf Mongoose

During one game drive, our tracking crew noticed a Southern yellow-billed hornbill hopping through the brush, snatching insects and moving at a faster pace than I’d seen around our campfire area. Ahead of the hornbill, we could see sleek gray bodies darting through the brush: a troop of dwarf mongoose! Kersey, our guide and tracking teacher, explained the symbiotic connection. Hornbills will often associate with dwarf mongoose troops, waiting for them each dawn at the entrance to their termite mound burrow. As the mongoose forage across the land, they disrupt insects with their passing — creating opportunistic foraging for the following hornbill. In return, the hornbill will alarm when an aerial predator appears, allowing the mongoose to quickly seek cover.

Experiencing this interaction left me wondering about my home ecosystem:

How many birds have symbiotic relationships with the mammals where I live?
Which birds in my home ecosystem are primarily insectivores? (And, which insects are available in each season?)
What have I missed, when I’ve focused on “just” seeing the bird or listening for a call?