Thursday, February 28, 2008

No Way Home

No Way Home: The Decline of the World’s Great Animal Migrations by David Wilcove is a new book about the disruption of animal migration routes. In the introduction, Wilcove lists the four major problems. First is habitat destruction which may be at either end of the journey or at rest points along the route. Second, obstructions such as dams, roads, fences, cell towers. Third, overexploitation (the word makes me question if plain old exploitation is acceptable, but onward) meaning hunting for food by more ‘advanced’ methods than traditionally used, such as miles long drift nets in the ocean.


Most interesting, most unpredictable, and most out of our control, climate change which can affect ecological relationships in many ways as species (plant and animal) which depend on each other for food, pollination, etc. react differently to rapid changes. An example is given involving when oaks leaf out, determining what the tannin (a defense against insects) level of the leaf will be when a moth is ready to lay eggs on it and when those eggs become caterpillars. Will migrating bird species arrive at the proper time to eat some of those eggs or caterpillars? If they get there too late, they’ll not only be going hungry but the forest will be damaged by the larger population of moths.


From the air come the bird migrations of course, and one of those fascinating cases of pulling one strand of the web and finding everything else connected: the rapidly declining population of red knots (a bird which breeds in northern Canada and winters in South America) was discovered to be caused by increased taking of horseshoe crabs by humans in the Delaware Bay area. Eating horseshoe crab eggs was a very important stop on the birds’ migration route.


The author also looks at the migrations of monarch butterflies, grasshoppers, and dragonflies. A few years ago, I walked out the front door and found myself in the midst of a migration which led to first amazement and then a constant grin as I walked down the street surrounded by dragonflies. Here in Duluth, we’re also fortunate to be on a major raptor migration route as they funnel around Lake Superior. Tens of thousands of the birds pass through each fall at Hawk Ridge.


On land, there’s a chapter on Africa which I skipped, and one primarily dealing with bison. This chapter includes discussion of the only remaining wild herd in its native range, which is in Yellowstone. Because many of these bison carry brucellosis, if they dare to leave the park on a seasonal migration due to snow at higher elevations, they are shot to prevent possible infection of local cattle. The irony here is that this disease was first introduced to North America via cattle imported from Europe.


From the water, we get discussions of whales (incidentally, Sea Shepherd has chased away the Japanese whaling fleet again) and salmon and most interestingly to me, sea turtles. Living at sea but laying eggs on beaches, the turtles have to deal with the worst of both worlds—fishing gear and shoreline development. At sea, they’ll also eat plastic, mistaking it for the jellyfish they prefer. Turtles living near areas with large human populations are also developing tumors believed to be related to human pollution. As more humans live by the shore, more raccoons and other turtle egg eaters follow them. For millions of years newly hatched sea turtles have headed for the brightest spot at night—the ocean. Now that brightest spot is often a porch or street light.


Looming ahead for them to deal with are the effects of global warming. Rising sea levels may eliminate the beaches they return to for nesting. The incubation temperature of their eggs determines the sex of the hatchling; in most species, higher temperatures will result in females. This has been observed even within a nest: the warmer central eggs will produce females while the eggs on the cooler edges will become males.

2 comments:

Lisa J. said...

The irony here is that this disease was first introduced to North America via cattle imported from Europe.

Yes, but you have to be intelligent to appreciate irony. ;)

Stephanie said...

How desperately sad. I may look into getting this book (to add to my list and pile).