Evolution / behaviour question

A very brief search of talkorigins yielded nothing so I’ll ask here.

How is the migration of birds explained? Many birds migrate yearly to a destination they could not possibly have known about when they first made the trip. The Arctic Tern migrates ~11000 miles.

My best guess is that it started back when the continents were merged. Things got a little chilly and food became scarce in the north so birds made their way south and found greener pastures. South gets cold, move north. By the time the continents split, the locations had already been ingrained into the breeds (i.e. this location is safe, good food). The only difference is that it took a little longer to get there. The adjustment was so small that there was never any reason to change the pattern of behaviour.

There’s no need to go that far back. (In any case, the last time the continents were merged into Pangea was the Permian, which far predates the origin of birds.) Many modern migratory patterns have surely become established since the end of the Pleistocene.

Establishment of migratory patterns can be explained as a gradual process. As climatic conditions change, some members of the species begin wintering farther and farther south (or migrating farther north in the spring). As long as this continues to enhance survival, the processs will continue, until the wintering grounds can be very far away from the breeding grounds.

Among American Wood Warblers, all degrees of migratory patterns can be found. Some species living in southern areas are basically sedentary. Some species migrate only a short distance, from the northern US to the southern US. Others go to Mexico or the West Indies, others to Central America, while others go all the way to South America. The more extensive migrations almost certainly evolved from shorter-range ones.

Migratory patterns in some birds have been found to be under genetic control. For example, in one European species, one population migrates in one direction, while another migrates in a different one. If you cross individuals from the two populations, the offspring migrate in an intermediate direction. What the genetic and neural mechanisms for this may be is very poorly understood.

Animals on the African plains migrate without flying.

That’s all well and good but they are not continent hopping. It’s one thing to wander around following food, it’s another to take wing and land somewhere near Buenos Ares only to eat enough for the strength to come back to Portland.

Although African swallows do fly… European swallows are non-migratory, but can nonetheless may be able to carry a coconut if two carried it together on a line.



Sadly, it’s stuff like this that makes me love the internet. Our idle time is now harnessed into searching out the answers to questions that no one cares enough to answer and, if need be, making up the questions as we go.

The north-south routes for land birds are either over land (Europe-Africa, North-South America) or connected by chains of islands that are not too far apart (Asia-Australia). Before the formation of the Panama land bridge, there were islands along this route, as there still are on the route through the West Indies. The gaps between these island chains are mostly less than 100 miles, and are no great deal for even a small land bird to cross.

Routes through such island chains can develop easily since birds may be able to see across the gap to the next island, especially from high up. Otherwise, some birds do overshoot, and can end up on even remote islands. As long as there is enough food, they may survive to migrate back and thus establish a new route.

Did you read my first post? This is generally not the way new routes are established. They are produced by gradually extending migratory ranges over time, not by some sudden leap into the unknown.

What the hell is this supposed to mean?

My reading of the question:

makes the genetic issue the key. (I may be reading something into the question that isn’t there.)
How does a species effectively pass a map on genetically. And, how does a species evolve the carto-missive gene? It seems like the ability would have to evolve before it could be used begging the question of how the ability could benefit the species if it’s not in use.

I think your posts answered this OP pretty damn well. I agree completely. I could perhaps add a few cites, but nothing else to your explanation.

Perhaps Greenback is talking about the Monty Python swallow joke reference :rolleyes: **Nature’s Call ** made? :confused:

Birds don’t necessarily know how to migrate. Cranes for instance need to be shown how to do this. If food is abundant for instance Cranes won’t migrate period. For example, there are Cranes and ducks that live year round in Florida, they have plenty of food so they don’t leave.

Geese are the same way. In Chicago we have many corporate parks and the Geese have no preditors and lots of food people throw out. These geese never leave.

The trigger seems to be a lack of food or the unavailablity of safe nesting sites. As long as these two things are abundant the birds stay.

There are exceptions though. There are kinds of birds that will migrate without being shown and will leave even abundance, but in general, for all animals, the availabity of easy food will over ride even the toughest inbred genetic instincts. This explains why they can put sharks and other fish in the same tanks. By humans feeding the sharks, the sharks get so lazy they never even bother to look at a fish they may have to chase

This we don’t really know.

It’s just an extension of short-distance orientation. Obviously, animals benefit by being able to navigate over short distances within their home ranges. They need the ability to be able to return to roosts, food sources, etc. Long distance navigation is just an extension of the capabilities needed in short distance orientation, although new abiilities specific to long distance migration (e.g. celestial navigation) may be evolved over time.

Part of the problem the OP may be having is confusing the tendency to MIGRATE with the ability to NAVIGATE. These are two separate things, though obviously long-distance migration depends on sucessful long-distance navigation.

Thanks for the explanations Colibri. I think your last statement explains where my misunderstanding came from.

And yes, I was commenting on Nature’s Call’s post.

My understanding is that they don’t. Species pass on a genetic drive to move in a certain direction at certain times of the year, not a map. This is certainly the case with the SE Asian cuckoos, with birds from southern Australia migrating to northern Australia in winter, while birds from Northern Australia migrate to Indonesia and Malaysia. If eggs from Southern individuals are hatched in the North the young will migrate all the way to Indonesia while Northern eggs hatched in the south will only migrate to northern Australia. That seems to suggest that the migratory instinct is purely a “fly north for 3 weeks when the day length is less than 12 hours” type of code. There is no suggestion that these birds are following a map of any kind.

Other species may have a more complicated system that does require some form of internal map reading, but I’ve never seen any suggestion that this is the case except where young birds learn by migrating with older indivuals.

That’s a logical fallacy. “A leads to B” doesn’t allow you to conclude “A therefore B”. Of course an ability has to evolve before it can be used. That doesn’t allow us to conclude that the ability has to be used before it can evolve. If a bird evolves that feels an urge to move south before it is driven south by hunger or extreme cold it may have a survival advantage overbirds that only migrate due physical to stress. That is a benefit all by itself.

I think I’m confusing bird migration with fish migration. I can’t find any birds that migrate to a specific place without having an older generation to follow.

If it is going to offer some advantage it does. There wasn’t an animal that just suddenly had wings. (TA DAH!) There were intermediate steps that offered slight advantages. Those intermediate steps had to be used to offer their advantages.

I think you’re using the word evolve in two different ways. An ability has to evolve before it can be used, yes? But it doesn’t stop there. The ability evolved from some other set of abilities and continues to change through use. There are latent abilities and vestigal abilities, but I don’t think animals evolve (spontaneously develop) wholly developed navigational abilities that, up to their advent in the species, offered no other benefit.

But, more to the point, an animal would have to evolve some type of genetic map transmission system without having any advantage for having it before they could genetically transmit the map that would then offer the advantage.

How about salmon finding their way back to the stream where they were spawned? That isn’t just a “swim in this direction” kind of instinct. Wikipedia says it may have something to do with the salmon’s sense of smell, but I’m not sure how that would work. They’d still need to know the general direction to head in since they are just roaming around in the ocean somewhere, no?

Can you provide some evidence of a fish that migrates to a specific place?

But you still haven’t shown that the ability to fly has to be used before it can evolve, which was your original contention. In fact you appear to have demonstrated exactly the oppoiste: that the ability to fly can evolve through a series of intermediate pre-flight steps.

I don’t think that anyone disputes that any intermediate steps themselves need to be useful to be selected for. That is a far cry from your original suggestion that a complete working map system has to spring from the ground fully formed in order to evolve at all.

I’ve only used it one way in this thread: for a trait to arise through variation in gene frequency.

Nor does anyone else. But this is very different to a claim that the ability can only evolve if it can be used before it evolves.

No. There is simply no reason to accept that.

Is there any evidence that salmon do find their way back to the stream where they are spawned more than we would expect by random chance? You’ll excuse me not taking an unreferenced Wikipedia claim as a reputable reference on this.

Yes, you are excused.

Some salmon do find their way to their streams of birth.

From: Bond, C. E. 1996. The Biology of Fishes. Saunders College Publishing. Page 604.

From: Love, M. 1996. Probably More Than you Want to Know About the Fishes of the Pacific Coast. Really Big Press. Page 99, the discussion of Pink Salmon.

I don’t really have a lot to add to what’s been said already other than that the migrations of fishes, while not nearly as long or impressive as the migrations of some birds, are amazing phenomena in their own right and the ability of salmon to locate their birth stream is stunning. (And astounding enough that I certainly don’t blame anyone for being suspicious of a Wikipedia cite on the matter. :wink: )

BTW, my refrence to wikipedia was not about whether or not salmon generally are able to find their “birth stream”-- that is not some obscure fact. My reference to wikipedia concerned the mechanism used-- ie., smell. I wasn’t sure if that was correct or if how it might actually work. For what it’s worth, the wikipedia article didn’t state that as a fact, it said:

OK, so there’s evidence of at least one species that largely rteurns to the home stream. But by the sound of it this is a species that largely sticks to the coastlines. Woudl that be right?

Thanks for that Wevets, though I will remain somewhat skeptical until I see a better reference than “The Bumper Book of Fish” published by “The Giant Press Co”. Such books are generally OK but they also tend to conatin their own share of errors and legends.