17 December 2007

Balene ucigase vanand in grup

Trei orca colaboreaza pentru a face un val suficient de mare incat sa dea o foca jos de pe un iceberg (2min40s):
The behaviour was first seen in 1979, but at the time it was considered a one-time moment of orca ingenuity. Now, Ingrid Visser of the Orca Research Trust in New Zealand and her colleagues report on six further observations of the animals using group hunting behaviour to divide ice floes, push them into open water, and create waves to wash animals off them into their waiting jaws. The behaviour has been seen only along the Antarctic Peninsula and nowhere else in the world, they note, including other icy orca habitats in the Arctic and Antarctic. [Visser, I. N. et al. Mar. Mamm. Sci. doi: 10.1111/j.1748-7692.2007.00163.x (2007).]
Ceea ce e cel mai spectaculos la comportamentul asta e faptul ca arata ca orcile sunt capabile sa separe actiunile in termeni de mijloace si scopuri si ca sunt in stare sa se vada unele pe altele ca agenti (sa inteleaga ce scopuri are altcineva). Pana acum nu era confirmat decat ca cimpanzeii mai sunt in stare sa faca asa ceva (in afara de oameni). De asemenea, balenele ucigase se recunosc in oglinda (chiar si o oglinda extrem de mica fata de dimensiunile lor): Tehnicile de vanatoare sunt probabil invatate si fac parte din cultura lor. Se pare ca diferite grupuri de orca au culturi diferite. De pilda tehnica prin care orcile prind foci de pe uscat sarind pe plaja e invatata:
Hunting school Both the beaching and the wave hunting seem to be techniques that pod elders teach to younger animals. The Argentinean orcas have been seen nudging youngsters onto the shore, encouraging them to try the tactic, often coming up alongside to demonstrate. In the group at the Antarctic Peninsula, young orcas are often present during the hunt, and adults sometimes put living seals back on the ice after catching them, seemingly so that the young can have another try. “This is orca culture,” says Visser. [...] Orcas (Orcinus orca) are not considered an endangered or threatened species; they are found in all the world's oceans. Some local populations, however, are threatened by changes to their habitat. Whether subsets of orcas with unique cultures should be considered separately is a matter that has not really been dealt with, he says. “Distinct social populations with specialized traditions are far more at risk than the genetic population, and our conservation policies need to reflect that,” says Astrid van Ginneken at the Center for Whale Research in Friday Harbor, Washington.
Fact about orcas:
Orcas have been known to feed on over 25 different species of whales and dolphins, including some that are much bigger than themselves (sperm whales, gray whales and even blue whales). Not all orcas eat other mammals though. The resident population off Vancouver Island, for example, eat fish, and their favourite food is salmon. Male orcas generally don't live as long as females. In the wild, males average 35 years or so, maximum 50-60 years, females average 50 years, maximum 80-90 years. However, one male, known as ‘Old Tom’ was reportedly spotted every winter between 1843 and 1932 off New South Wales, Australia. This would have made him at least 89 years old! Once in captivity, an orca's lifespan is drastically reduced to an average of only 5 or 6 years.