A falcon was recently tracked migrating from South Africa all the way to Finland. In 42 days she flew over 10,000 km in almost straight lines, at speeds of the 230 km/day.
The bird likes to follow the shorelines like that of the Red Sea as much as possible. Near Portsaid it flies to starboard and follows the Syrian and Med shore. The same for part of the Black Sea.
Magnetoception is the ability for certain animals to orient themselves based on the earthâs magnetic field. Magnetoception as it is called is used for navigational, altitude and location purposes by animals like dogs, cats, whales, sea turtles, pigeons, bees, fruit flies, bats, and other creatures. Also humans seem to possess this ability although in a small amount.
What I do not understand is how these birds could manage the compass deviation.
For short times and ranges this should not be a problem, but for extremely long ones.
Now, the deviation in South Africa is -22°, slowly changing to +10° in Finland.
Maybe they treat it like a great circle course where you have to change compass heading periodically. They do it every year so the gradual drift shouldnât bother them that much.
Maybe they donât know about what humans call the geographical poles, only about the magnetic poles, thus no deviation.
That the magnetic poles move over time doesnât matter to the birds and the bees.
When you live in the present and donât have a long historic perspective there is nothing but NOW.
What is the falconâs diet? Falcons typically prey on other birds as well as rodents, insects and other small animal. Birds as large as sandhill cranes, and as small as hummingbirds, have been consumed by falcons. Their typical prey items include shorebirds, ducks, grebes, gulls, pigeons, and songbirds . Peregrine falcons also eat bats, and they occasionally steal preyâincluding fish and rodentsâfrom other raptors.
Whatever it was the falcons that were able to find the more efficient path would have had higher survivals rates and thus successfully passed that ability on to offspring.
Early navigation traveling east / west in the Mediterranean faced the same problem. They did not adjust their compass course because they had used the same compass error to create their charts.
From Hutchins:
"If the cartographer uses a magnetic compass to make a chart and the navigator uses a magnetic compass to determine courses, and if both compasses show the same errors in the same places why would anyone care and how could anyone ever notice that the charts put the land in the wrong place?
Of course mariners who had better charts and better instruments would be at competitive advantage over other less efficient navigators. Same as the falcons only with instruments.
The only way to have the geographic compass directions is the noon sun; it gives the local true North or South. Indeed, without a sextant, it is not easy to determine the exact noon, but it returns always a good approximation and, hence, a virtual compass rose.
Near sub solar points, there is still the North or South ambiguity, but these birds must have other means to bridge this zone.
The route is probably mostly genetic induced, and less by own experience; with the following genetic selection.
The famous Monarch Butterflies do not make a complete voyage from the Rocky Mountains to Mexico and back to the Rockies; in the middle of the return flight, the females lay their eggs and die. This is completely geneticâŚ
I could imagine this:
The birds use the noon sun for the true geographic direction and, between two noon observations, they bridge the gap locally with some magnetic capabilities.
Complex reactions between a birdâs beak, eyes, brain, and ears allow it to accurately navigate across thousands of kilometers. Researchers have discovered a small spot on the beak of pigeons and some other birds that contains magnetite.
Magnetite is a magnetized rock, which may act as a tiny GPS unit for the homing pigeon by giving it information about its position relative to Earthâs poles. Researchers have also found some specialized cells in birdsâ eyes that may help them see magnetic fields.
It is thought that birds can use both the beak magnetite and the eye sensors to travel long distances, the so called flyways, over areas that do not have many landmarks, such as the ocean.
In humans, deposits of magnetite have been found in bones in our noses. So just follow your noseâŚ
When I was very young, my family was stunned by my ability to always know what direction we were traveling, even when sitting in my car seat in the back seat of the Buick. I donât even remember the first time that they recall me interrupting Mom and Dad, who were arguing in the front seat about which way to turn. I told them, apparently in a very calm voice, âEast is that way.â
That voice has dimmed in the latter part of my life, subdued by gyroscopes and gps enabled smart phones, but it is still there if I listen carefully while in a foreign city or stumbling down a backcountry trail.
Just to illustrate that this capability is widely shared in the animal kingdom, hereâs an amusing little video that just came across my desk about foxes using magnetic sense to help orient themselves when catching mice under the snow. The video doesnât explain HOW they use it and, from a little quick research, it appears that the scientists apparently havenât figured that out yet. But they have confirmed that the fox is much more likely to catch his mouse if he orients himself toward magnetic north! Apparently still a lot of scientific head-scratching going on about how heâs using that! Makes me wonder if the mice are using mag-sensing too?
Probably done entirely by direct visual navigation.
Diurnal prey hunting raptors have a foveal (central) cone density at least twice as high as humans (who have pretty good daytime resolution for mammals). Since the human fovea can resolve 1 minute of visual angle (about equal to the distance between individual cones), that would suggest that raptors can resolve visual angles as small as 30 sec. of arc.
Some of you navigators are probably way ahead of me on this, but something that is 1 meter in size is just at the threshold of human resolution (ie: subtends 1 min. of arc) at 3,437 meters distance. So if a man viewed vertically subtends 1 meter, that falcon can just make him out at about 7 km. distance. Individual recognition of course might well require a shorter distance!
And since central foveal cones are âwiredâ one to one with visual cortex cells in the brain, that means such raptors have a pretty densely populated visual cortex! Some day hunting raptors also have a second cone dense fovea to help spotting small visual angle targets.
That falcon probably cruised (as we see) until he spotted his handler and then dove right to him. He could probably see and recognize him clearly from well over 3000â elevation.
(After I served in the PHS Marine Hospital Service, I practiced ophthalmology for 35 years, and among other things, consulted a couple of times with a raptor rescue outfit.)
His flight path is interesting. A lot of 360âs and S-turns until he tucks his wings and dives for his handler. Sightseeing, covering his six or trolling for prey on the way?
was recently tracked migrating from South Africa all the way to Finland. In 42 days she flew over 10,000 km in almost straight lines, at speeds of the 230 km/day.
