Fake bee blood | How to count a million bats | Song of the indigobird
Fake honeybee blood lures pollinators to rare South African plant
A species of rare plant that grows in grasslands in eastern South Africa has been shown to manufacture the smell of bee blood -- to attract a scavenging fly that then pollinates the plant.
Jackal flies steal food from bigger predators, mostly spiders and praying mantises, and are alerted to the existence of this free meal by the smell of spilt blood, or haemolymph, of captured honeybees.
The flies are helped by the fact that mantids and spiders are messy eaters, says lead author Annemarie Heiduk, the scientist behind the discovery.
“They (the flies) sometimes even sit at the mouthparts of a mantid and suck up the little droplets,” she told me.
She and her team wanted to know why the plant – known to science as Ceropegia gerrardii – attracted the flies in the absence of real bee blood; jackal flies had been observed feeding on the plants' green star-shaped flowers for hours.
The team produced a solution in the laboratory that closely resembled the scent compounds emitted by the plant. Vials containing variations of these compounds were placed in the plants’ grassy habitat, and the team noted which ones effectively drew in the jackal flies.
The droplets secreted by the flowers were found to be full of protein and sugar -- evidently a sweet reward to the flies. Flowers from which the flies were excluded did not produce any fruit, the study found.
“We always associate flies in a negative context but they are extremely important to maintain biodiversity and to allow plants to survive and reproduce,” says Heiduk.
“Without flies, a lot of our biodiversity would not be there.”
A jackal fly feeding on the floral secretions of C. gerrardii | Annemarie Heiduk
How to count a million bats?
A team of international scientists has figured out an accurate way to count the number of African straw-colored fruit bats whose annual congregation in a swamp in northern Zambia is reputed to be the biggest mammal migration on earth.
Tourists from all over the world travel each year to Kasanka National Park to witness the breathtakingly massive swarms, which had previously been estimated to comprise up to 10 million bats.
Now, using simple GoPro cameras set up to encircle a small patch of forest in the middle of the park where the bats gather each October-December, scientists used AI to estimate that these straw-colored fruit bats do represent the heaviest congregation of bats on earth – around 300,000 kilograms (661,000 pounds) of biomass.
Their numbers are, however, significantly lower than previously thought: around 1 million at the time of the experiment.
To develop the AI, the scientists trained a computer program to automatically count the number of bats crossing the center of the frame of each image captured by the GoPro cameras over five consecutive nights as the bats went out to feed.
The cameras were found to be at least 95% accurate when the scientists manually counted some of the clips.
Kasanka’s fruit bats, which have impressive wingspans of up to a meter wide, converge on the park from across the continent. They then disperse as far as the Democratic Republic of Congo and South Sudan.
The bats are ‘ecosystem engineers’ – helping to spread tree seeds and maintain forests.
Keeping tabs on their numbers will be more important than ever.
Bats heading out to feed at Zambia’s Kasanka National Park | Sybryn | Wikimedia Commons
Nature Notes: Where the indigobirds lived
I grew up in a part of eastern Zimbabwe that is home to all four species of indigobird.
I would see some of these small finches each morning as I cycled to school along a dirt track that passed through a field.
The indigobirds -- which at that time were called widowfinches on account of the male birds’ all-black breeding plumage -- would fly up and perch on a telephone wire as I passed by.
I was reminded of this on a recent Sunday outing with my family to Harare’s Mukuvisi Woodlands nature reserve.
My daughter and I spotted some village indigobirds rifling through leaf litter beneath some musasa trees.
Near to them was a flock of red-billed firefinches. The male village indigobird is known to mimic the song of these firefinches and there’s a good reason for that.
Indigobirds don't raise their own chicks. They are parasitic. During the breeding season the females lay their eggs in firefinch nests.
In my final year of high school, I recall that two US scientists came to stay with us. They were doing research on indigobirds, and the husband-and-wife team spent all day out in the grassy field near our house where the indigobirds lived.
The data they gathered was for their long-term study on these birds. Among the many things they discovered was that a female village indigobird forms a strong bond with the firefinches that raise her.
When she herself is ready to breed, she will only accept a male indigobird if he mimics the song of her foster parents.
