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www.thevillagenews.co.za
30 September 2020
MY ENVIRONMENT
The extinction of species By Dr Anina Lee
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avid Attenborough's documentary on the rate at which species are going extinct as a result of human activity has had a big impact on viewers. Whether anyone is going to change their lifestyles as a result, remains to be seen. Extinctions often happen gradually, so that when people notice and become concerned, it's often too late. For example, when last did you find your windscreen covered in insect splat? Here's another example, although not from our shores. Does anyone know what happened to passenger pigeons? Passenger pigeons The passenger pigeon (Ectopistes migratorius) was a North American wild pigeon species that went extinct by 1914. Ectopistes means ‘moving about or wandering’, and migratorius means ‘migrating’. Its common name is derived from the French word passager, meaning ‘passing by’. Clearly they didn't carry passengers. But they were migratory, travelling in large flocks between the eastern parts of Canada and the south-east of the Length: 32cm USA.
massed together that they frequently broke the limbs of the trees by their weight. In the morning the birds flew out in large flocks scouring the countryside for food. At night they returned to the roosting area. The migratory flights of the passenger pigeon are described in writings of the time as spectacular. Although the birds flew at an estimated speed of about 80 km/h, observers reported that the sky was darkened by huge flocks passing overhead, often continuing from morning until night and lasting for several days. But despite their vast numbers (estimated to be about five billion), passenger pigeons were doomed from the moment that Europeans arrived in North America. In the 19th century, passenger pigeons were so numerous that there were contests to shoot as many of them as possible during a specific period. In one competition, the winner shot 30 000 birds. The settlers ate passenger pigeons in massive amounts, but mainly they were killed because they were perceived as a threat to agriculture. As Europeans migrated across North America, they thinned out and eliminated the immense forests that the pigeons depended on. By 1850 the destruction of the pigeons was in full swing. Ten years later observers noticed that the numbers of birds seemed to be decreasing, but still the slaughter continued.
The habitat of the passenger pigeon was mixed hardwood forests. The birds depended on the vast forests for their spring nesting sites, for winter 'roosts', and for food. They ate beechnuts, acorns, chestnuts, seeds, and berries found in the forests. Worms and insects supplemented the diet in spring and summer.
One of the last killing competitions of passenger pigeons took place in Michigan in1878. Here 50 000 birds per day were killed, and the contest continued for nearly five months. When the adult birds that survived this massacre attempted second nestings at new sites, they were soon located by the professional hunters and killed before they had a chance to raise any young.
In the winter the birds established roosting sites in the forests of the southern states. Each roost often comprised tremendous numbers of birds. They were so crowded and
As the species was already dying out, the last big flock of 250 000 birds were shot on a single day in 1896. That same year, a sighting of the last passenger pigeon was recorded in
Louisiana. It was also shot. Pigeon superpower Pigeons have unique navigational superpowers. The carrier or homing pigeon is a domesticated version of the wild rock pigeon (Columba livia). Wild rock pigeons have an innate ability to find their way home over long distances – hence the name homing pigeons. Today's homing pigeons have to be carefully bred and trained to do the same. If taken away from home, pigeons can find their way back in a remarkably short time. In fact, homing pigeons have been known to 'home' from 1 500 kilometres away, and they can travel an average of 70 km/h, with bursts of up to 120 km/h. This ability has made them valuable as messengers since at least the time of the ancient Egyptians. Homing pigeons were used extensively in both World Wars. Several birds even received medals for their service in delivering critical messages during wartime! But how do they find their way home over such long distances? Despite many scientific studies over the years, no one yet fully understands how homing pigeons navigate. Several theories may explain at least part of the processes at work. Scientists now believe that homing pigeons have both compass and mapping mechanisms that help them navigate. The compass mechanism helps them to fly in the right direction, while the mapping mechanism allows them to compare where they are to where they want to be (home). A homing pigeon's compass mechanism likely relies upon the sun. Like many other birds, homing pigeons can use the position and angle of the sun at a particular time to determine the proper direction for flight. The mapping mechanism kicks in closer to the home when they remember specific landmarks. For example, they may follow a railway line to where it intersects with a road, then change direction to follow the road home. Pigeons have a prodigious memory
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TOP: In the 19th century, passenger pigeons were so numerous that there were contests to shoot as many of them as possible during a specific period. In one competition, the winner shot 30 000 birds. PHOTO: Indiana History Blog ABOVE: Despite their vast numbers – estimated to be about five billion – passenger pigeons were doomed from the moment that Europeans arrived in North America. PHOTO: Reddit LEFT: The passenger pigeon (Ectopistes migratorius) was a North American wild pigeon species that went extinct by 1914. PHOTO: Getty Images and can recall more than a thousand images, even years later. Some researchers believe homing pigeons use magneto-reception, which involves relying on Earth's magnetic fields for guidance. They have found that homing pigeons have magnetite crystals in their upper beaks that would allow them to detect magnetic fields easily. More recent research, however, suggests that homing pigeons may also rely upon low-frequency infrasound. These low-frequency sounds are inaudible to human ears, but they're created by nearly everything,
including the oceans and Earth's crust. Homing pigeons may listen to these sounds until they recognise the signature sounds of their home roost. Some research suggests that pigeons may also be guided by smell. If all this seems unbelievable, just remember that pigeons have unimagined superpowers. But despite superpowers, passenger pigeons and another million species are no match for the destructive superpower of humans. We are undoubtedly able to cause extinctions such as Attenborough identifies. The Sixth Extinction is all too possible.
