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Wednesday, April 20, 2011

Cetacean celestial navigation

This is very cool. It's actually possible (although the article doesn't say so) that the whales are using something similar to the Polynesian "starpaths". The map below gives enough detail to try to reconstruct what they would have been seeing in the sky and get some clues. Here's a very quick computation based on the map below.

The majority of the tracks appear to be about 150° True. Picking a central position of 30°S and 030°W and a mid-date of 15 October, from sunset to sunrise we see:

Time Star Magnitude Hc (height) Zn (Bearing)

2049Z Evening Twilight

2100Z Achernar 0.6 33° 141°
2200Z Achernar 0.6 41° 142°
Canopus -0.8 03° 153°
2300Z Achernar 0.6 49° 144°
Canopus -0.8 09° 147°
0000Z Achernar 0.6 56° 151°
Canopus -0.8 17° 142°
0100Z Achernar 0.6 61° 163°
Canopus -0.8 25° 138°
0200Z Canopus -0.8 34° 134°
Avior 1.7 20° 148°
0300Z Canopus -0.8 43° 136°
Avior 1.7 27° 145°
0400Z Canopus -0.8 52° 134°
Avior 1.7 35° 144°
Acrux 1.1 10° 160°
0500Z Canopus -0.8 60° 147°
Avior 1.7 42° 145°
Acrux 1.1 15° 155°
0600Z Avior 1.7 50° 149°
Acrux 1.1 21° 152°

0642Z Morning Twilight

Is it possible, based on this, that humpback whales could be using Polynesian-style starpaths to navigate across oceans? Yes, maybe. Canopus itself is awfully bright, and throughout the course of the evening stays somewhat close to our base course of 150° true. Add in a few 1st and 2nd magnitude stars and it starts to look a lot better. But then the question arises of how the whales would know which of these less bright stars would correct for the motion of Canopus around the pole. Canopus spends a lot of the night at around 135° True, some 15° off of our base course. If they were steering by Canopus alone we'd expect to see that 15° offset in their courses, but we don't. So, either the whales are using some awfully sophisticated starpaths (more sophisticated than the Polynesians would have attempted), or there's something else going on here. Will think more on this tomorrow, I hear my bed calling.


WIRED SCIENCE-- An eight-year project that tracked humpback whale migrations by satellite shows the huge mammals follow uncannily straight paths for weeks at a time.

The results suggest a single migratory mechanism isn’t responsible. Instead, humpbacks may use a combination of the sun’s position, Earth’s magnetism and even star maps to guide their 10,000-mile journeys.

“Humpback whales are going across some of most turbulent waters in the world, yet they keep going straight,” said environmental scientist Travis Horton of the University of Canterbury, whose team will publish their findings April 20 in Biology Letters. “They’re orienting with something outside of themselves, not something internal.”

Humpback whales feed during the summer near polar oceans and migrate to warm tropical oceans for the winter, where they mate and calves are born. A one-way trip can last upwards of 5,000 miles, making the cetaceans one of the farthest-migrating animals on Earth. (One was tracked migrating 6,200 miles).

To better understand humpback migrations, Horton’s colleagues embedded satellite tags in seven South Atlantic and nine South Pacific whales from 2003 through 2010.

Each tag contained a battery-operated transponder that beamed its location to the researchers. The tags lasted from four weeks to seven months before falling out; altogether, they provided one of the most detailed sets of long-term migratory data for humpbacks ever collected.

“You can’t stick a large whale in a box like you can with a bird to study its migratory behavior. This is why detailed field data on whales is so important,” said research biologist John Calambokidis of the Cascadia Research Collective, who wasn’t involved in the work.

The researchers found that, despite surface currents, storms and other distractions, the humpbacks never deviated more than about 5 degrees from their migratory courses.

In about half the segments mapped by the researchers, humpbacks deviated by one degree or less.

“When we first starting seeing data, we thought, ‘Wow, these are really, really straight paths,’” said marine biologist Alex Zerbini of the National Oceanic and Atmospheric Administration, a co-author of the study who led the satellite-tracking effort. “We immediately wondered how they accomplish that.”

Decades of research on long-range animal migrations has identified geomagnetic and sun-tracking mechanisms, but that work focuses primarily on birds. Humpbacks don’t seem to rely on either method alone.

Earth’s magnetism varies too widely to explain the whales’ arrow-straight patterns, and solar navigation requires frames of reference that water doesn’t often provide. “The open ocean is an endless horizon of blue,” Horton said.

Horton suspects humpbacks rely on both mechanisms, and perhaps the position of the moon or stars. His team is preparing to submit a second study on reference frames in marine mammals, birds, fish and reptiles. After publishing that work, Horton hopes to further investigate the humpbacks’ abilities.

Calambokidis suggested a fourth mechanism for steering: long-distance songs that can carry for hundreds or thousands of miles underwater, and may provide navigational cues or help migrating whales coordinate their movements.

“These whales are clearly using something more sophisticated to migrate than anything we’ve surmised,” said Calambokidis. “I’m really looking forward to seeing what this team does next.”

1 comment:

  1. The astronomical data table didn't format properly at all, will try to fix in the morning.