Female dragonflies fake death to avoid unwanted mating


This video from England says about itself:

Common Hawker Dragonfly (Aeshna juncea)

13 February 2015

Common Hawker Dragonfly, filmed in the New Forest, Hampshire, UK. One of the rarest species in the New Forest, occurring only sporadically in a few isolated locations. Video includes male and female of the species, plus a mating pair.

From New Scientist:

27 April 2017

Female dragonflies fake sudden death to avoid male advances

By Sandrine Ceurstemont

Female dragonflies use an extreme tactic to get rid of unwanted suitors: they drop out the sky and then pretend to be dead.

Rassim Khelifa from the University of Zurich, Switzerland, witnessed the behaviour for the first time in the moorland hawker dragonfly (Aeshna juncea). While collecting their larvae in the Swiss Alps, he watched a female crash-dive to the ground while being pursued by a male.

The female then lay motionless on her back. Her suitor soon flew away, and the female took off once the coast was clear.

“I was surprised,” says Khelifa, who had never previously seen this in 10 years of studying dragonflies.

Female moorland hawkers are vulnerable to harassment when they lay their eggs since, unlike some other dragonflies, they aren’t guarded by their male mates. A single sexual encounter with another male is enough to fertilise all eggs and copulating again could damage their reproductive tract.

Khelifa found that the females often retreat to dense vegetation near ponds at this time, probably to hide. And they often act dramatically when they emerge.

High-speed plunge

He observed 27 out of 31 females plummeting and playing dead to avoid males, with 21 of these ploys successful. Plunging at high speed is risky though, and according to Adolfo Cordero-Rivera at the University of Vigo in Spain, it may be a strategy that they use only in areas with lots of dragonflies. “Females may only behave in this way if male harassment is intense,” he says.

Few animals have been caught feigning death to trick suitors. The behaviour has been seen in a species of spider (the males use it to improve their chances of mating), two species of robber fly and a type of mantis.

Playing dead to avoid predators, however, is more common and has been observed in dragonflies. “It’s likely that females expanded its use to overcome male coercion,” says Khelifa.

Khelifa is interested in finding out whether the behaviour is unique to species that lay eggs alone or whether it is more widespread. Using extreme tactics to resolve sexual conflict isn’t unique to moorland hawkers: in their damselfly relatives, for example, females eat their partner.

Biggest ever Swiss dinosaur skeleton discovered


This video is called My Plateosaurus Tribute + my favorite Plateosaurus Pictures!

From swissinfo in Switzerland:

Triassic park: oldest Swiss dinosaur skeleton found

July 1, 2015 – 18:55

The largest dinosaur skeleton ever found in Switzerland has been uncovered in a clay pit in northern Switzerland. The eight-metre skeleton of a plateosaurus is thought to have been around 25 years old when it died.

“This herbivore lived 210 million years ago and was discovered in the Upper Triassic geologic layer,” said Ben Pabst, who has been leader of the dig in Frick, canton Aargau, since 1976. The dinosaur’s head has yet to be found.

Plateosaurus was a bipedal herbivore with a small skull on a long, mobile neck, sharp but plump plant-crushing teeth, powerful hind limbs, short but muscular arms and grasping hands with large claws on three fingers, possibly used for defence and feeding.

Unusually for a dinosaur, instead of having a fairly uniform adult size, fully grown individuals ranged from 4.8-10 metres long and weighed 600-4,000 kilograms.

The site in Frick is known around the world for the density of dinosaur skeletons.

“We have here an unbelievably large site. So far we have been able to determine an area with a diameter of three kilometres,” Pabst explained on Wednesday, adding that one hectare will yield some 500 animals and that for every 100 herbivore dinosaurs there is one carnivore.

Museum

Around 210 million years ago, Frick was flat, very hot, tropical and criss-crossed with rivers. Pabst assumes that at various times a range of dinosaurs, which weighed several tons, got stuck in the boggy land and died of thirst.

Since many complete skeletons of legs have been found, he believes the animals were mummified by the heat.

The theory that the dinosaurs sank in mud was strengthened by the fact that the plateosaurus in question was found with its legs spread.

The Frick site has an annual budget of CHF50,000 ($52,800) and the work is heavily reliant on volunteers. The latest find is too big for the Frick dinosaur museum, so a renovation is being considered.

Red-crested pochard, new species on Dutch island


This is a red-crested pochard video from the Lake of Geneva in Switzerland.

Dutch birdwatcher Debby Doodeman writes about going by boat to De Kreupel, an island in the big IJsselmeer lake, on 17 May 2015.

There, she saw a male red-crested pochard. Maybe, his female partner sat on a nest not far away? Maybe there will be an answer to that, later at De Kreupel.

Red-crested pochards had never been seen on De Kreupel before. About 400 couples of this species nest in the Netherlands.