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Why Do Whales Beach Themselves?

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Humans have observed marine mammals stranding themselves on land since at least the first century CE, when the ancient Romans and Greeks recorded beaching incidents. Modern marine biologists are only able to determine the cause of a beaching about 50 percent of the time, according to the Woods Hole Oceanographic Institution, and the reasons they find are varied.

Often the cause is obvious injury or illness. Disease or wounds from predators can leave an animal too weak to keep itself afloat, and at some point it gives up and lets the tides wash it ashore.

Cases where a group of animals beach themselves together, and not all of them exhibit signs of trauma, are more puzzling. One explanation biologists offer is that whales and dolphins, which hunt and travel together in groups called pods, fall victim to their own social structure. If the group leader or dominant animal is sick or hurt and runs ashore, the rest of the group might follow. Other times, the pod may just get itself stuck by a low tide after hunting or traveling too close to shore.

In some instances, mass beachings have occurred shortly after active use of military sonar in an area. In 2000, for example, 17 animals from four species (Cuvier’s beaked whale, Blainville’s beaked whale, Minke whale, and the spotted dolphin) were found beached within a 36 hour period in the Bahamas the day of, and after, a U.S. Navy sonar exercise. A joint Navy and National Oceanic and Atmospheric Administration (NOAA) investigation soon concluded that the tactical mid-range frequency sonars used by the Navy ships “were the most plausible source of the acoustic or impulse trauma” that occured. The evidence suggests that sonar may have both physical and behavioral effects on marine mammals.

Some animals also beach themselves purposefully as a hunting tactic. Killers whales, or orcas, frequently chase pinnipeds, like seals and sea lions, into the surf zone and onto shore, where the prey has to make a clumsy transition from swimming to walking in shallow, turbulent water. As the prey struggles to escape, the orca launches itself, or rides a wave, onto the beach and grabs the prey in its jaws. After the meal is secured, the orca can either wriggle back into deeper water or let a large wave lift it off the ground and back out to sea.

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Animals
This Octopus Species in Northern Australia Can Hunt on Dry Land
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YouTube

Most octopuses live in the ocean—but in northern Australia, a small, shallow-water species takes to land in search of food. Abdopus aculeatus is the only octopus that’s specially adapted to walk on dry ground. Using its long, sucker-lined arms, the slimy sea creature pulls itself along the shoreline as it searches tide pools for crabs.

Witness Abdopus aculeatus in action by watching BBC Earth’s video below.

[h/t BBC Earth]

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Weather Watch
Rising Temperatures Are Killing Off African Wild Dogs
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Over the last few decades, images of fluffy white harp seals, polar bears, and penguins have become shorthand for climate change's creeping destruction of our planet. But the poles aren't the only ecosystems in danger. A new study published in the Journal of Animal Ecology finds that rising temperatures near the equator are making it much harder for African wild dogs to survive.

"When people think about climate change affecting wildlife, they mostly think about polar bears," lead researcher Rosie Woodroffe of the Zoological Society of London told The Guardian. "But wild dogs are adapted to the heat—surely they'd be fine."

To find out, Woodroffe and her colleagues analyzed data from packs of African wild dogs (Lycaon pictus) in Kenya, Botswana, and Zimbabwe. The dog packs have been under scientist surveillance for years—some since the late 1980s—and at least one dog per pack is fitted with a radio collar.

The researchers overlaid information about local weather and temperature with data on the dogs' hunting habits, the size of each litter of pups, and how many pups from each litter survived.

These dogs are creatures of habit. Adults rise early and leave the den for a morning hunt. They range over their large territories, chasing antelopes. At midday, when the Sun is highest, they return to their pups with food. They may go out again in the evening as the temperature drops.

But like the polar bears' glaciers, the dogs' environment is gradually heating up. All three countries saw a temperature increase of about 1.8°F over the study period. This may not sound like much, but for the dogs, it was plenty. Between 1989 and 2012, the number of pups per litter in Botswana surviving to their first birthday dropped from 5.1 to 3.3. Dog packs in Zimbabwe saw a 14 percent decrease in pup survival; in Kenya, the rate declined by 31 percent.

"It's really scary," Woodroffe said.

"If you are an animal who makes your living by running around really fast, obviously you are going to get hot. But there are not enough hours in the day anymore that are cool enough to do that. It is possible that some of these big areas will become too hot for wild dogs to exist."

Woodroffe and her colleagues were not anticipating such clear-cut results. "It is shocking and surprising that even right on the equator these effects are being seen," she said. "It illustrates the global impact of climate change." 

[h/t The Guardian]

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