I’m not sure whether other countries have people who regularly race flocks of pigeons, but around here it’s a common sight in the sky to see a small flock circling trying to find their bearings (I think?).
One thing has always puzzled me, however. The birds fly in small groups, circling, and they all seem to be able to turn at the same time. There doesn’t seem to be any sort of delay between the first bird turning and the last one, it’s instantaneous. It also seems to be very rare for the pack to split up, in other words, they all seem to turn in the same direction, by the same amount, at the same time, keeping formation.
I never hear any audible signals from the lead bird, so to speak, yet they do this regularly. How is it possible?
How is it possible for a pigeon to fly from an undisclosed position back to it’s home, as well? Do they have a built in compass (which should surely mean they have an accurate way of measuring distance, too?) or do they navigate by the sun / stars?
Like most birds (except owls) a pigeon’s eyes look to the side and not forward. It is not difficult to believe that piegons have evolved the same sort of clustering technique schooling fish use. Turning ensemble is probably triggered by a combination of depth perception and peripheral vision.
Some computer modelling in the form of “boids” has been done on flocking behavior. You can read about some such models here. There are also numerous other links on that site for more information.
From what I understand, Zenster is one the right track. When The flock turns, there actually is a very slight delay between the “lead” bird changing course, and the rest of the flock following suit. It is a visual phenomena, and the birds will watch each other to make sure that they are where they should be. The motivation behind this of course, is not to be left outside of the flock. The bird that is left behind is the bird that becomes lunch.
As to the choice of direction, I think it arises from one bird folowing another, and having another following that bird. Eventually it snowballs, and the whole flock will shift that way. Of course this happens fast, but, as birds have been flocking for millenia, it is second nature to them. If you think about it, it’s not much different than cars on a busy highway. When one cars slows or speeds up, others will be forced to change along wih it.
People can do it too. Put a few experienced formation pilots in an aircraft each and it will look like they are flying as one. However, it’s just a case of each guy/gal making sure they are in the right position relative the lead aircraft, communications are not necessarily required.
This one explains that the birds do use the earth’s magnetic field to help them navigate – they have a magnetically-sensitive organ in the brain. They also use the position of the sun, memory of landmarks close to home and even their sense of smell to locate their home loft. Apparently each loft has its own characteristic smell.
But the earth’s magnetic field moves by a couple of degrees every year. It’s marked on virtually every map out there, as it makes a tremedous difference when taking bearings over large distances. How does a bird compensate for this?
How will the birds react when the magnetic poles flip, like is being predicted?
+MDI - no worries, the magnetic poles will flip when the pigeons are flying next to pigs, like is being predicted… Now, about that “flocking behaviour”…
I’m pretty sure there’s strong evidence (in the orientation of the atoms making up the sea beds near underwater fault lines) to suggest that the poles do actually flip from time to time.
Even if they don’t flip, there’s still a problem with the moving magnetic field which I know personally happens from walking and using OS maps. How do the pigeons cope?
The poles do indeed shift, but it is very infrequent. I think what radar ralf is trying to say is, by the time the poles flip again, pigs will have evolved to the point where they too can conquer the wild blue yonder. To answer your question though, if the poles flipped, you would have a lot of north flying birds suddenly going south, and getting really confused.
As far as the shifting magnetic field goes, it really isn’t a huge problem. Birds will use other senses as well to find their way home, such as sight or smell. The magnetic fields get them close to where they want to be, and from that point, other navigational aids can be put to use. Remember, from a birds eye view, you can see a heck of a lot. The field shifts slow enough that the birds can change their mental maps easily enough, as well. It is probably along the lines of “oh, when I was at this point in the magnetic filed last month, this mountain was beneath me . Now it’s over there. Time to readjust my bearings”.
This does bring up another interesting question though. From the bird’s point of view, what is the “resolution” of the magnetic field? How close can they get to home using that method alone?
Bear in mind, up to this point all of my bird work had involved the nesting habits of the black capped chickadee, and my knowledge of migratory bird behaviour is a mish mash of facts from my bird, and animal behaviour classes.
How infrequent are we talking about here? I tried to google it, but the first several pages were all about the catastrophic pole shift that will make the earth tilt on it’s axis, uh, this past May. Let’s assume, for the moment, that that didn’t happen. :dubious: What’s the real deal? Has it even happed since migratory birds evolved?
Archaeopteryx is considered to be the first bird, or failing that, proto-bird. It had feathers and may have been capable of short burst of flight, much like a turkey. Definitely not big on migrations I would imagine. It dates back to the Jurassic period, so it’s about 150 million years old.
I’m actually on my way out for a bit, but when I get back I’ll dig up some more concrete links. A google search for Paleomagnetism will turn up some more info as well, if you have time.
Okay, I’m back, with the promised info. Here is a good page for more information on pole reversals. Two relevant quotes:
And
From this latter quote, it is hard to judge what effect such a field reversal would have on a bird dependant on navigation via the magnetic field. I would think that a long term shifting, in the order of 100 – 1000 years, the birds would adapt readily. It would only require a simple change in the way that they do the math that they use to figure out which way to go. Flipping the map 180 degrees, so to speak, which I think could be accomplished over time, being accomplished by the use of spatial landmarks to re-orient themselves magnetically. On the short term, they would indeed go in the opposite direction at first. From this site:
This deals with bobolinks, but the basic idea is the same as in pigeons. From here:
As far as the existence of migratory birds being around during a shift period, I was unable to find any hard data, but I would imagine that there were. As migration is a behavior, it doesn’t show up in the fossil record, save for similar skeletons being found in areas separated by large distances. Even then it’s tricky to say, because it could be migration, or just a very large range. There is evidence of sea birds dating back to the cretaceous period (144 mya – 65 mya), more towards the latter end (Ichthyornis. Scroll down ¾ of the way). Was it migratory? Did it navigate via the magnetic field? I’m not sure. Again, things like that don’t fossilize that well. But the skulls are somewhat similar to modern birds, though there is less area devoted to the brain (Compared to the Common Loon and compared to a Sandwich Tern[Ichthyornis skull on top in both pictures]). I think that covers all I wanted to say. If I think of anything else, or if clarification is needed, I’ll come back and add it.
I think you people are getting things mixed up. The earth’s magnetic field is useful in navigation just because it is pretty constant over time, not because it points in any particular direction. The changes are very small so as to be unnoticeable to a pigeon over 10 or 20 years. Since the pigeon is not going to live that long anyway it does not matter. For all practical purposes to a pigeon the magnetic field is constant so, if it learns to navigate by it in its infancy it can navigate by it the rest of its life. You would need centuries or millenia to make a significant difference.
Well, I think so, sailor, but maybe that’s kind of the crux of this part of the question. If a migratory bird species had an evolutionary predisposition, and instinct, to say “follow the magnetic field when the weather changes,” wouldn’t that bird be SOL in, say, 10 generations when each generation flew further east and less south when the winter came? Or is the magnetic abilty simply a guide to help it along some other method which takes it south (say, “take off in the morning with the sun on your left and keep the magnetic field directionally constant all day.”)
Thanks for that meat, Emperor Penguin, that’s pretty cool. We’ve established that somehow the birds adapt to the shift, as we see species constant through several shifts.
Fortunately, it appears not to have happened since mankind started using magnetism for navigation and that when it does it will be slow enough for us to make the kinds of adjustments sailor mentions.
Heh. Can you imagine a sudden shift at the wrong time? Columbus, when his ship pulled back into Spain without seeing the New World: Mama Mia! The earth! She is not round – she is finite but unbounded!
