The Bat Hawk is a lethal cross between a falcon and a nightjar. It has the largest open-mouth gape of any raptor, and eats bats in single gulps.
By Rex Graham
Biologists in Africa watched one against the fading glow of sunset as it swallowed a swift-sized bat every 3 minutes during one 20-minute feeding frenzy. On average, it ate a bat every 5 minutes. During 6 consecutive evenings, the hawk flew back and forth across the opening of Ngwerere Cave near Lusaka, Zambia, feeding on most of the 9 bat species that spewed into the sunset.
Bat Hawk fast food
“It is not intuitively obvious how Bat Hawks subdue and ingest bats so quickly without injury,” the biologists from the University of Zambia said in the journal Biotropica. The Bat Hawk released every other bat it captured, possibly after being bitten. However, on some evenings it ate every bat it caught. (Bat Hawks also eat swifts, swallows and other high-flying, insect-eating birds.)
The large-eyed, Bat Hawk is an aptly named specialist. It exploits a little-appreciated ecological niche – the twilight torrent of biomass that emerges from caves.
Finding Bat Hawks
“Fortunately, Bat Hawks tend to favour a particular roost site, and once found, sightings can be almost guaranteed,” said Clayton Burne, a guide with Rockjumper Birding Tours. Such encounters give birdwatchers a chance to experience one of the world’s most unusual hawks that has mystified scientists.
“The species’ enlarged gape suggests convergent evolution with swifts, swallows, and nightjars, and permits the ingestion of relatively large intact prey,” a team of Polish, Czech and Australian researchers said in the journal Mammal Review. “Its prey is, moreover, typically captured, processed, and swallowed in flight, so that its behaviour resembles that of aerial feeders more than that of other raptors that usually process their prey at a perch.”
Bats always on menu
In a meta-analysis of 1,500 cases of bat attacks in 109 countries worldwide, Bat Falcons were the biggest threats among 143 species of raptors. Occasionally, gulls, butcherbirds and roadrunners attacked bats at cave entrances and other roosts. Crows and related Corvid species in urban areas are important opportunistic predators of bats that roost in buildings and other man-made structures. Most falcons, hawks and kites are opportunistic predators of bats, but there are no published reports of bat predation by South American caracaras.
Bats are easy prey for all avian predators that can detect them. The Polish, Czech and Australian researchers said owls capture over 90% of bats that are eaten by birds. Of course, bats have evolved a nocturnal lifestyle, and when they leave their roosts during daylight hours they are 100 to 1,000 times more likely to be eaten than at night.
The eyes of Bat Hawks are adapted to low-light twilight. Their wings are long and pointed for maneuverability, and their large gape easily accommodates small and medium-sized bats. In Zambia, they ate an average of 7 bats per night. Their favorite species were the echo-locating Bushveld horseshoe bat (Rhinolophus simulator), Sundevall’s Leaf-nosed Bat (Hipposideros caffer), Percival’s Trident Bat (Cloeotis percivali), Wood’s Slit-faced Bat (Nycteris woodi) and Large-eared Slit-faced Bat (Nycteris mactotis).
Neglected ecological niche – bat caves
Some caves in Tropical parts of the world are home to millions of bats. About 70% of bat species are insect-eaters, the rest eat fruit, and a few eat fish or drink blood. Female bats usually give birth to one offspring per breeding season, timed to optimize food availability. Dynamic, healthy bat populations are based on high survival rates of individuals.
If a single Bat Hawk eats 7 bats per night, it would consume 2,555 bats per year. “At the Ngwerere Cave, predation of this magnitude would eliminate the entire bat community,” the Zambian biologists said. High risk of predation by emerging before darkness must be rewarded by the abundant emergence of a diverse and abundant supply of insects at the same time.
If the number of bats in Ngwerere Cave declines, Bat Hawks would probably move on. A very precise balance may exist between bat and hawk. “Few raptorial birds have become so specialized,” the Zambian biologists said.
Bats are threatened by humanity as well as natural predators:
- People in North America and Europe who regard bats as nuisances frequently kill them for no other reason.
- South American Vampire Bat Control programs also eliminate bats indiscriminately.
- Asian and Australian fruit-growers target fruit-eating bats.
- Since 2000, wind-power turbines have caused the most mass casualties of bats.
- More intense storms, flooding, heat waves, drought and other impacts of global warming may cause mass die-offs.
- White-nose Syndrome, a fungal disease, has spread across eastern North America, devastating some populations of hibernating U.S. bats, according to U.S. researchers.
In caves, smaller numbers of Cave Swiftlets sometimes share space with huge numbers of bats. Ecologists are awed by the vast, under-appreciated insect-eating services of bats.
“Their faeces and urine provide the main basis for the entire food web in many caves,” Malaysian bat researcher Liz Price said in the journal Ambient Science. “The cave food web can be quite complex, but is primarily based on the guano.”