Title: Furry Logic: The Physics of Animal Life
Author(s): Matin Durrani, Liz Kalaugher
Release year: 2016
Publisher: Bloomsbury Sigma
Why in Database: A popular science book which is a review of interesting “phenomena” in animals, along with a large Historical background, that is, explains not only “how animals do it (eg they use a magnetic field)” but also describes the scientific process thanks to which the given phenomena were learned. In this context (of the magnetic field) there is a large, almost twenty-page piece devoted to turtles in the book. We do not quote the whole of it, only a few selected fragments. Beyond these pages, turtles are mentioned a few more times in the book, mostly in the form of later references to the aforementioned passage about turtles.
The first seven quotes we have quoted come from the mentioned above large fragment:
Sometime back in the twentieth century, probably in 1915, a crew of fishermen from the Cayman Islands was catching green turtles off the coast of northern Nicaragua. As was the custom, the men branded their initials on the reptiles and loaded them into a boat heading for Key West in the US. But there was a huge storm off the Florida Keys and the boat never made it; it capsized and the turtles escaped into the sea. A few months later, the same fishermen, again off Nicaragua, were amazed to spot their initials on two turtles in their nets; the escapees had doggedly headed back from Florida – at least 1,150km (715 miles) away – to the feeding grounds from where they were snatched.
The captain of the crew regaled the tale to Archie Carr (1909–87), a pioneering sea-turtle investigator at the University of Florida. Carr detailed the story in his 1956 book The Windward Road: Adventures of a Naturalist on Remote Caribbean Shores, a publication that led to the formation of the Brotherhood of the Green Turtle. Today this organisation is dubbed, less romantically but more gender-neutrally, the Sea Turtle Conservancy.
‘Prior to Archie Carr’s work, fishermen in many parts of the world were aware that turtles migrated long distances but the scientific community was not,’ says Ken Lohmann of the University of North Carolina, US, who has unravelled many of the mysteries of turtle navigation. ‘It took careful work by Carr and others, tagging turtles and recapturing them, to establish that the turtles did migrate long distances and frequently returned to the same areas to nest year after year.’
Lohmann began investigating turtles after studying direction-finding in lobsters and sea slugs. His turtle research was meant to be a short-term project, but he’s still going strong after more than 25 years. Lohmann is clearly a man who enjoys his job. ‘Turtles are a lot of fun to work with,’ he says. ‘They’re charismatic animals. The hatchlings are cute, they have big eyes and it helps, of course, that they don’t bite – they’re essentially defenceless.’ Turtles don’t remain small for ever: a nesting adult female can be over 1.2m (4ft) long and weigh more than 110kg (240lb). ‘They’re large and kind of prehistoric-looking, it feels like working with dinosaurs,’ Lohmann adds.
‘Just about the worst place for a small turtle to be is in clear shallow water over a reef near land – there are lots of predatory fish looking up at the turtles and lots of seabirds looking down,’ says Lohmann. The young turtles have no good way to escape. They’re too buoyant to dive more than a metre below the surface so they can’t get away from birds. And they swim much too slowly to escape fish.
When Lohmann replicated the magnetic field on the east Florida coast, the turtles swam east, the direction that would pick up the Gulf Stream if they were in the sea rather than a super-sized paddling pool. When he reversed the magnetic field around the turtles, most of them turned and swam in the opposite direction. ‘That was the initial evidence demonstrating that turtles can sense magnetic fields,’ he recalls.
After a 15,000km (9,000 mile) journey lasting years, the turtles do something that’s equally incredible, this time for its precision, not the distance involved. ‘Eventually, when they’re fully mature and able to nest, at about age 20, they migrate back to the same area of the coastline where they started out,’ says Lohmann. Adult females journey north to the beach of their birth between May and August every two or three years, depending on how much food they’re getting. They scoop out a hole with their rear flippers, lay around a hundred eggs and cover them with sand, repeating the process some 15 days later. Males may make the trip to mate with females every year, but it’s hard to tell as they stay in the water.
This proves, Lohmann believes, that turtles locate the beach of their birth by its unique magnetic signature.
Hatchling turtles imprint on the beach’s magnetic field strength and inclination as they leave, just as a chick imprints on the first animal it sees as its mother. ‘Young turtles learn the magnetic signature of their home beach, retain that information, and then use it as adults to navigate back years later,’ Lohmann says.
To a turtle a floating carrier-bag looks like a jellyfish, one of its favourite foods. But a turtle with a stomach full of indigestible plastic is a turtle that will starve. The same goes for balloons; those charity balloon releases help worthy causes but they don’t do turtles any good at all. And, as with many reptiles, the number of males and females that hatch from a batch of eggs depends on how hot they get. A loggerhead turtle nest at 28˚C will hatch only males, one that’s at 30˚C will spawn a 50:50 mix of males and females, while one that’s at 32˚C will produce girl-power alone. That means climate change could make the male loggerhead turtle – and ultimately the species – extinct.
The last fragment we quote comes from a later part of the book:
Mankind’s technology, much of it based on physics, has damaged many animal habitats. Coastal power lines and steel in beach-side hotels could disturb the magnetic fields that loggerhead turtles use to navigate home.
Author: XYuriTT
