Category Archives: Natural History

Arctic Terns

2018 Trip to Iceland, Birds, Natural History

 

We saw a colony of Arctic terns in southern Iceland. One of these birds attacked me. I guess I got too close to its nest. They are very protective.

One of the most fascinating aspects of birds is their ability, often truly amazing, to migrate, often over amazing distances, and in amazing circumstances.    Why do birds, unlike most animals migrate in the first place?  How do they navigate?  How do they know where to go?   How can they migrate so far, often under very adverse conditions?  In fact, to me the very notion of migration is a vast mystery that I will never understand, no matter how much I learn about it.   Just as one example, among many, some species of shorebirds, a relatively short time after giving birth to their young abandon them to their own devices while they fatten up for the long migration.  Then the adults head south many thousands of miles away, often to South America.  Amazingly, the young, who have never been anywhere in their short lives other than northern Canada, fly south on their own without any guidance from the adults, and turn up at the same place as the adults some weeks behind the adults.  How do they do it?  It is very difficult for us mere humans to fathom such incredible abilities.  It is a profound mystery.

Why does the Arctic Tern migrate literally from one end of the earth to the other, and then later back again?  What drives the bird to do that?  Why do they travel so far to go from one seemingly inhospitable place to another?  I will never understand these things, but will never tire to trying.

Some recent information about Arctic Terns is just downright amazing. The Arctic tern is justifiably famous for its astonishing migration. It is one of the most astonishing stories in a natural world filled with astounding stories. It flies each year from its breeding grounds in the Arctic in the spring and then back again after the summer. The shortest distance between these two points is 19,000 km (12,000 mi). This is the longest migration of any animal in the world! It flies about 2 times farther than scientists earlier believed because its route is not straight. It meanders.

Recently scientists have been able to install very small transmitters onto them so that their track could be monitored. One Arctic tern followed a zig-zag pattern from Greenland to Antarctica and back again each year and in the process racking up 44,000 frequent flyer miles (or 71,000 kilometers), as National Geographicdescribed them.  This is 4,000 miles or 6,440 km more than its nearest competitor the sooty shearwater. The researchers who found out this new information estimated that because the birds often live to be 30 years old over their lifetime they travelled about 1.5 million miles (2.4 million kilometers) which is equal to 3 trips to the moon and back![1]

Until recently scientists could not find a tracker light enough to be carried by a tern. Now they use one that is 1/20thof an ounce or 1.4 grams. The researchers also learned that terns often stop for month in the open Atlantic Ocean possibly to “fuel up” on small fish and crustaceans before continuing their awesome (for once that word really does apply). Even more surprisingly, they don’t take the shortest route. Instead they zig and zag literally across the ocean and back again! Some wondered why they would zigzag so much. For example, the terns from Greenland don’t fly straight up or down the Atlantic. Instead they “hopscotch from Antarctica to Africa to South America to the Arctic.”[2]Even though this is a detour of several thousand kilometers because they zigzag across the Atlantic Ocean, The birds appear to be following huge spiraling wind patterns in the atmosphere, avoiding flying into the wind,” according to Carsten Egevang one of the researchers.[3]

Though scientists are not sure why these amazing birds take such a long journey nearly from pole to pole, they believe it must be that the terns find rich feeding grounds in the waters of the poles. Why else would they do it?

 

 

[1]“World’s Longest Migration Found–2X Longer Than Thought,”National Geographic(Jan 2010)”

 

[2]“World’s Longest Migration Found–2X Longer Than Thought,”National Geographic(Jan 2010)

[3]Carsten Egevang, “World’s Longest Migration Found–2X Longer Than Thought,”National Geographic(Jan 2010)

Deserts

Natural History, religion

 

What is a desert? That is not as simple as I thought. Deserts are defined by water—or rather, by the absence of water. Dryness and sunlight are what deserts are all about. Buckets of sunlight, rather than buckets of rain. Plants or animals that don’t like that cannot survive here. Some plants, amazingly, even prefer the south facing side of the mountain.

Geographers define deserts as land where evaporation exceeds rainfall. I was surprised to learn that there is no specific amount of rainfall that serves as an agreed upon criteria as what is and what is not a desert. Deserts range from extremely arid regions to those that are ample for the support of life. Geographers classify rainfall into semi-deserts that are ones that have precipitation between 150 and 300 to 400 mm per year. So called “true deserts” are those that have rainfall below 150 mm per year and extreme deserts as those with rainfall below 70 mm per year.

Deserts occupy about 26% of the continental areas of the world. Deserts occur in 2 distinct belts. One is between 15º and 35º latitude in both the Northern and Southern hemispheres—the Tropic of Cancer and Tropic of Capricorn.

There are 14 deserts in the world (depending on who is counting) with an area larger than 52,000 sq. km (20,100 sq. mi.). It may surprise some that the largest desert in the world is not the Sahara desert. It is only the second largest. The largest is Antarctica not often thought of as a desert, but that is what it is. Antarctica has 14,000,000 sq. km. and the Sahara with 9,000.000 sq. km.

There are 5 distinct deserts in the American Southwest: the Sonoran, The Chihuahuan, The Great Basin, and the Mojave. Some also include the Colorado as a separate desert. Although each is a desert, each is also different.

The Sonoran Desert, where we have been living for the 4th year,  is semi-arid desert and it covers part of southern California and Arizona as well as northern Mexico. Because of summer’s “monsoons” and winter storms this is the wettest of all the North American deserts. It is most well known for its iconic tall Saguaros cactus some of which can reach 50 feet in height.

The Great Basin is the most characteristic of the Southwest with its canyon, mesas, buttes, and cliffs.

The Mojave Desert is a large desert that spreads across northern Arizona, Nevada, and California. It is dry most of the year but a small amount of winter rain can bring it to life.

The Chihuahuan desert is found mainly in Mexico but reaches north to Albuquerque, New Mexico, so we spent some time in it too.

One of the things that struck me about the desert was the amazing way that plants grow there. If you have a pine forest, unlike our pine forests, the trees are not crowded. They are well spaced. Where shrubs cover a mountainside, they do so in the most spotty of fashions. Vegetation never covers the ground, even where it grows best. The plants demand space from all around them—like snooty royalty.

The plants even want some separation from those fantastic rocks that I love so much. Usually they are found well-spaced, like surprisingly obedient school children. Willa Cather put it well. She said,

From the flat red sea of sand rose great rock mesas, generally Gothic in out-line, resembling vast cathedrals. They were not crowded together in disorder, but placed in wide spaces, long vistas between them. This plain might once have been an enormous city, all the smaller quarters destroyed by time, only the public buildings left.