Octopus geometry | Hyena den ‘timeshare’ | Invaders boost kestrels | A charismatic tree
Octopuses in South Africa do complicated sums before dinner
A new study suggests that octopuses do complicated geometry to measure where to drill holes in the shells of helmet snails, which they must do to inject venom into the molluscs to get the creatures to release their grip on their shells.
The study was carried out in False Bay, South Africa, home to Octopus vulgaris and three of its main prey types. In addition to the helmet shells, the shells of abalone and kelp limpets were also studied by marine biologist Gareth Fee, the lead researcher behind the study published in Marine Biology.
All of the shells he analyzed bore the drill holes made by octopuses. Fee compiled heat maps that highlighted the different drilling zones on the shells.
Abalone shells and kelp limpets were drilled with low and medium precision respectively, probably because the muscles attaching them to their shells are larger and provide bigger targets.
But the helmet shells were drilled with extreme precision. Over half the holes in the 78 shells analyzed were drilled on the spire at an angle of 45° and 90° from the lip, he and his co-authors report.
The team behind the research says the findings prove that the octopuses use the spire, the lip and aperture of the helmet shells as “a landmark” to figure out where to drill their venom holes.
“It most certainly takes great intelligence to do this effectively,” says Jannes Landschoff, a co-author of the paper.
Shells of the South African helmet snail | H. Zell | Wikimedia Commons
‘Time-share’ in Kenyan wilderness promotes peaceful coexistence between predator and prey, new study shows
Scientists monitoring hyena burrows in northern Kenya have discovered a new phenomenon: den-sharing with porcupines and warthogs, two mammals that would normally appear on the hyenas’ menu.
The scientists believe this cohabitation may be a result of mutual respect for each other's “formidable weaponry”. While the hyenas are armed with bone-crushing jaws and teeth, porcupines have rigid spines on their backs, and warthogs have sharp tusks.
The threats posed by these weapons are amplified in the close quarters of a subterranean den, the scientists write in a new study published in the African Journal of Ecology.
“We assume that these dens have a subterranean layout with branches and chambers that are occupied by the different species,” they add.
Other factors could help to foster peaceful co-existence between these animals: time-share, thanks to the warthogs being diurnal and vacating the burrow during the day; and "room service" courtesy of the hyenas bringing in a plentiful supply of bones which, despite being vegetarian, porcupines enjoy.
There were, however, times when all three species were in the den at the same time, and the researchers noted that they sometimes used the same entrance within minutes of each other.
The team examined hyena droppings at the two monitored burrows in the Lewa Wildlife Conservancy. None contained traces of porcupine or warthog. Yet, hyenas from separate clans that weren’t cohabiting preyed on porcupines and warthogs elsewhere in the study site.
No pushover: warthogs are armed with sharp tusks | Bernard Dupont | Wikimedia Commons
Mauritian plant invader supports breeding success of endangered kestrels
An invasive tree is helping to support the endangered Mauritius kestrel, while at the same time threatening island biodiversity.
Geckos – the main prey of the kestrels – are abundant thanks to the Malagasy travellers’ tree, a species that was imported from Madagascar in the 1700s and is now overwhelming Mauritian evergreen forests.
The trees, which have long stiff leaves arranged in large fans, provide food and shelter for native day-geckos. When the geckos sun themselves on the leaves they become easy prey for the kestrels. Geckos form a disproportionately high ratio of the kestrels' diet, and are credited with boosting their breeding success, according to the study published in the Journal for Nature Conservation.
Conservationists now have to perform a delicate balancing act by removing the travellers’ trees without undermining the recovery of the kestrels, which came close to extinction in the early 1970s. Just four of the hawks were left alive in the wild back then. Their population currently stands at 350 or so.
Replacing the invasive travellers’ tree with native plants that are also highly suitable habitat for geckos is seen as key to both aiding the kestrel and reducing the negative impact of travellers’ trees.
A suitable native replacement may include the hurricane palm, whose numbers have been severely reduced in Mauritius’ remnant evergreen forest patches. Like travellers’ trees, hurricane palms support large numbers of geckos.
The Mauritius kestrel is a specialist gecko hunter | Josh Noseworthy | Wikimedia Commons
Nature Notes: the manketti tree
The manketti tree. When I saw it for the first time this month its branches were stripped almost bare ahead of the southern African winter.
The tree typically grows on the deep Kalahari Sands of western Zimbabwe. But those sands also stretch into parts of central Zimbabwe, which is where the 80,000-hectare (198,000-acre) Mafungautsi forest reserve and its unique flora -- including the manketti tree -- is found.
The manketti tree is now a personal favourite for me, up there with the likes of the baobab and the sausage tree. Before this trip the closest I’d come to these trees was via their nuts, known as mongongo nuts, that are extracted from the hard fruit and sold in some shops in Harare.
The tree is also known as the false balsa. Its timber was once used as a substitute for that ultra-light wood. In fact, on my trip to the forest this month I met a man who, as a boy, had built model airplanes from manketti wood.
Thankfully the manketti tree is not commercially harvested for its timber, but is left standing for something far more valuable: the oil. This is expressed from the nuts. It is bottled and sold as an essential oil for both skin and hair.
