Foxes in northern henhouse

Categorie(s): Ecology, thematic lessons

 Humans thinking to improve nature can be terribly wrong!
A good example of the unexpected effect of human intervening in nature:


Foxes may not graze, but a new scientific study describes how their arrival on Aleutian Islands destroyed rich grasslands and left only sparse tundra. The authors of the report, which appeared in Science, say this transformation shows how an entire ecosystem may go into a tailspin if just one new top carnivore shows up.

The inadvertent experiment began in the late 1700’s and continued into the early 20th century as fur traders looking to expand their supply released non-native arctic foxes and, in some cases, red foxes on more than 400 Alaskan islands. Some died out, but many populations survived.
The new habitats included much of the Aleutian archipelago that curves west toward Asia. Except for the occasional polar bear rafting in on winter ice, the windswept islands had few predators before.

The botanical impoverishment that has resulted is the reverse of what usually happens when a new meat-eater comes along.
“Traditionally, the predator eats the grazer; the grazer no longer eats the green stuff; and the habitat gets more green,” said Dr. Donald Croll, a professor of biology at the University of California, Santa Cruz, and the lead author of the report.
An example of the more usual routine is in Yellowstone National Park, where returning wolves, preying on sapling-browsing elk and confining the wary survivors to areas where they can see wolves coming, have touched off a resurgence of willow, aspen and other vegetation.
The contrary effect in the Aleutians, once sorted out, has a simple explanation. The grazers on these islands were grass- and seed-eating Aleutian geese, which are smaller cousins of Canada geese. The foxes drove the geese near extinction, which would have been a boon for grasses except that the foxes also feasted on the eggs and hatchlings of puffins, auklets and other ocean-feeding seabirds they found brooding in vast numbers almost everywhere.
Some islands lost almost all birds except for cliff-nesting species. And as ground-nesting birds faded, so did their nutrient-rich excrement, or guano, which had been a natural fertilizer.
The research team concluded that islands with no foxes received an average 361.9 grams per square meter yearly. Fox-infested islands get just 5.7 grams per square meter of guano per year.
You ever smell one of those rookeries?” Dr. Croll asked. “That is the odour of ammonia, like in fertilizer. Even the wind scatters it around.” Without the regular subsidy of nitrogen and potassium-rich nutrients winged in from the sea, grasses lost their competitive edge over tundra shrubs and herbaceous plants.

The origins of the project lie in the patient observations of G. Vernon Byrd, a Fish and Wildlife Service biologist at the Alaska Maritime National Wildlife Refuge. He has been studying the ecosystem for decades. Despite foxes, the islands remain home to more than 10 million seabirds of 29 species. Mr. Byrd is an avid birder. As a young naval officer in the late 1960’s, Mr. Byrd, a North Carolinian, arrived at a base on Adak Island in the Aleutians. He loved a place most sailors abhor. When his hitch ended, he asked to be left there. His stunned commander called in a psychiatrist. After his sanity was affirmed, Mr. Byrd recalled, “I walked over to the Fish and Wildlife office and signed up.”

He saw what foxes had done to bird populations. He noticed hardly any grass on islands with foxes, but plenty on those without them. While helping to restore the island of Amchitka, the site of early underground nuclear tests, he observed that splotches sprouted where a colleague’s torn fertilizer sack had dribbled. He saw grass thriving around nutrient-rich caribou bones. And guano’s fertilizing function is well known. Mr. Byrd started cooperation with Dr. James Estes, a ecosystem specialist from the University of California, Santa Cruz who, in turn, recruited Dr. Croll, who added more colleagues.

Every August from 2001 through 2003, the team braved brutal weather, freezing fogs and rocky landings to sample plants and soil on nine islands infested with foxes and on nine that were not. Test plots proved that given some fertilizer, remnant grasses regained their advantage. The numbers left no doubt that the Aleutian foxes had driven down the grasses by indirect guano deprivation.

The birds and grassy expanses should rebound in coming decades. For several years, Mr. Byrd and others in the refuge have been eradicating foxes with traps set along Aleutian shores in late winter and spring when, with birds away from nesting grounds, the hungry animals forage along the beach for crustaceans and washed-up edibles. Several thousand foxes have been eliminated and 40 islands have been cleared.

One of the cleansed islands is called Rat, which brings up another twist in a never-ending battle against alien, bird-eating Aleutian predators. Shipwrecks are not uncommon. When a vessel runs ashore, Fish and Wildlife personnel work as hard to protect the land as they do to protect the sea from their contents. Rodents can run amok in seabird colonies too or, as Mr. Byrd put it, “rat spills are a lot worse than oil spills in the long term.”

From New York Times 2005-03-29


  1. What was/were the reason(s) why people imported foxes on the islands?
  2. The text calls the situation an “inadvertent experiment”. An experiment contains a hypothesis, a prediction, a setup and a result plus conclusion. Describe the parts of the story that can be seen as hypothesis, prediction, setup, result and conclusion.
  3. In Yellowstone Park wolves (that had disappeared from the park long ago) were reintroduced recently, with positive effects on the vegetation. Explain why wolves can enrich the vegetation.
  4. Formulate in your own words how the foxes impoverished the nature, even if there are still millions of birds on the islands.
  5. Explain why rats imported from ships ‘are a lot worse than oil in the long term’.
    (What happens in the long term with the oil, and what with the rats?)
  6. Guano is widely used as fertilizer. Is adding guano in general good for nature? Explain why or why not.

                                                                                                                                          Arctic fox in summer