It is one of South Africa’s most iconic birds, and its numbers are in decline, mostly due to climate change. But scientists studying the Cape rock-jumper say the bird has an unlikely ally that boosts its chances of raising chicks: wildfires.
But things changed after wildfires swept through South Africa’s Western Cape Province that year, including part of the reserve.
Rock-jumpers started moving into the newly-burnt area, which had previously been uninhabited by the birds, and there were higher rates of nestling survival.
“We were actually quite surprised at how quickly birds began scoping out the new area after the burn,” said Oswald, a recent PhD graduate at South Africa’s Rhodes University. She was the lead author of the study.
The fires had depleted the thick plant cover used by the birds’ main predator: a snake known as the boomslang, Afrikaans for “tree snake”. Despite its name, the boomslang is at home in the treeless fynbos, a unique habitat of short shrubs and flowers growing on the rock-studded hillsides that the rock-jumpers call home (the birds get their name from their habit of bounding over rocks).
The male rock-jumper, a thrush-sized bird with a chestnut-coloured breast and charcoal head struck through with chalky white lines, is emblematic of South Africa’s fynbos.
Camera traps set up by Oswald and her colleagues showed just how formidable a predator the boomslang is: it accounted for most of the deadly attacks on nestlings during the three-year-long study; more than mongooses, honey badgers and rats.
Climate change may be aiding the snakes. The rock-jumpers’ breeding season normally starts in August, at the end of the southern African winter. But the earlier the birds began to breed, the more chance they had of escaping snake attacks, as the reptiles were far less active in the cold.
“In 2018 we started noticing nest predation by snakes at the end of September when temperatures started getting above 20°C or so, which meant that any rock-jumper nestlings that were not close to fledging by this time had a decent increase in risk of predation,” Oswald said.
Linked to fire
The Cape rock-jumper is one of just two rock-jumper species in the world; both are only found in South Africa and Lesotho, the tiny mountainous kingdom within South Africa’s borders, and both are classified as near-threatened by the International Union for Conservation of Nature because of declining numbers.
The 2017 wildfires that swept through the research site altered things for the better (from the rock-jumpers’ perspective).
Oswald now believes rock-jumper abundance is cyclical, and linked to fire.
“Birds in thick fynbos may just need to wait it out for another wildfire before they can start again having some breeding success,” she said.