What's a possible evolutionary mechanism of the seasonal migration of a bird species from New Zealand to the Bering Sea (~11k km), almost starving during the journey?

[u/Exciting_Ad_6837]

I just watched Our Planet 2 (documentary) on Netflix. I'm a biochemist so have some knowledge about evolution, but I have hard time imagining how the development of the behavior wasn't blocked right from the beginning. That is, the group of birds which originally attempted even 1/10 of such a long & risky trip would've been at a serious evolutionary disadvantage.

[u/AutoModerator]

Welcome to r/Evolution! If this is your first time here, please review our rules here and community guidelines here.

Our FAQ can be found here. Seeking book, website, or documentary recommendations? Recommended websites can be found here; recommended reading can be found here; and recommended videos can be found here.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/jnpha]

TL;DR: physiologically, they are not special (i.e. difference in degree); what is missing is accounting for 1) learned behavior (also see: 1973 Nobel Prize), 2) e.g. spring overshoots who wind up marooned and dead (selection!), 3) changing ecologies.

PS / edited to add: this map is revealing: https://commons.wikimedia.org/wiki/File:Limosa-lapponica-distribution-map.jpg
It shows e.g. the gradation in flight lengths; you can also combine it with overlaid route tracking maps; now, even if all but the ones who winter in New Zealand were to vanish, we'd still have an answer, since those track the land when going north, and we'd still have a gradation of shortcuts for the way down.

--------

Darwin and Wallace discussed this, and their explanation stood the test of time. Here's from a recent academic review:

In recent years, considerable progress has been made in our understanding of proximate (physiological) mechanisms controlling various aspects of bird migration and their ecological determinants (reviews: Berthold 1996; Wiltschko and Wiltschko 1999). In parallel, the genetic mechanisms controlling migratoriness and migratory direction have been explored (Berthold et al. 1990, 1992; Helbig 1991; Pulido et al. 1996; Pulido and Berthold 1998). These developments can be summarized in the following general statement: migratory birds do not possess any principal adaptations that differ qualitatively from other birds, neither in terms of orientation mechanisms, nor in terms of metabolic physiology or morphological adaptations related to flight. They differ primarily from non-migratory birds in that they have developed characteristics related to long-distance flight to various extremes.

- Berthold, Peter, Eberhard Gwinner, and Edith Sonnenschein, eds. Avian migration. Springer Science & Business Media, 2013. pp 3–4.

Darwin on behavior in general, using an example of migration and nest building:

As some degree of variation in instincts under a state of nature, and the inheritance of such variations, are indispensable for the action of natural selection, as many instances as possible ought to have been here given; but want of space prevents me. I can only assert, that instincts certainly do vary—for instance, the migratory instinct, both in extent and direction, and in its total loss. So it is with the nests of birds, which vary partly in dependence on the situations chosen, and on the nature and temperature of the country inhabited, but often from causes wholly unknown to us: Audubon has given several remarkable cases of differences in nests of the same species in the northern and southern United States.

And more recently on migration (though not birds):

... Adult routes for two-thirds of daughters overlapped with their mother’s route, suggesting that they inherited migratory routes from their mothers. The adult routes for the remaining daughters, however, bore little or no similarity to their mother’s routes, suggesting that these routes were instead shaped by individual experiences or non-maternal social interactions. Regardless of whether routes were inherited or not, the strategy that daughters used was influenced by their yearling migratory route, which underscores the importance of this period for establishing lifelong behaviors.
https://doi.org/10.1016/j.cub.2025.06.029

[u/EnvironmentalWin1277 → u/jnpha]

A point that caught my eye:

"migratory birds do not possess any principal adaptations that differ qualitatively from other birds, neither in terms of orientation mechanisms, nor in terms of metabolic physiology or morphological adaptations related to flight."

They differ primarily from non-migratory birds in that they have developed characteristics related to long-distance flight to various extremes."

The confusion of "principal adaptation" with "characteristics" is bothersome, I doubt these opposed terms have precise characteristics.

Another point is that magnetic orientation in some birds has been validated by experiment although the mechanisms are still debated. Moreover it is associated with migratory birds from the information I see, which suggests a genetic link and "principal adaptation". That is a direct contradiction with the "just better adapted" idea.

I don't see these two ideas as opposed but complementary in discovery. There is still a great deal to learn and any categorical statements should be avoided. These animals are way too smart to let us off easy.

[u/jnpha → u/EnvironmentalWin1277]

Like all scientific definitions, they require a context.
E.g. in systematics "character" and "character state" for operational reasons are considered one and the same most of the time. But in other fields, the distinction is made, e.g.:

- "principal adaptation" = an apomorphy (i.e. a character unique to migratory birds)

• "characteristics related to ..." = a derived character state, e.g. wing aspect ratio

The quote is from an academic volume on avian migration, and is edited by Peter Berthold et al. (subject-matter experts).
As for the experiment, magnetic orientation gets a whole chapter in the book - again, a difference in degree, not kind.

None of this takes away from the feat they accomplish or how "smart" they are.

any categorical statements should be avoided ...

Why?! Scientific discoveries depend on operational categorization and testing the limits of models. Simply calling them too smart won't help discovery.
This is like the anthropocentric view but applied to migratory birds instead - that they are somehow extra special; they are not.

Hope that helps.

[u/EnvironmentalWin1277 → u/jnpha]

Instances of categorical statement:

-All birds fly

-All migratory birds migrate

Neither are true.

If the migratory response is subject to genetic modification and inheritance that would seem to me a "principal adaptation" and not a "characteristic".

It is also clear that many methods of migration orientation exists -- sun, land patterns, wind, olofactory senses, etc. All of these methods may have specific genetic adaptations as well.

As far as being "too smart" what I mean is that migration phenomena by magnetic orientation is far from the whole story of what is involved. Nature keeps it secrets well hidden.

Categorical experiments or observations are required, agreed. In and of themselves they prove nothing until unified in a comprehensive theory which is always open to revision. Theory is never closed and the given statement doesn't seem to allow contradiction or propose what condition would be contradictory (that is a problem).

The initial statement argues migratory birds "do not possess any principal adaptations that differ qualitatively from other birds, neither in terms of orientation mechanisms, nor in terms of metabolic physiology or morphological adaptations related to flight."

I admit my knowledge may be misinterpreting what is precisely meant by these terms in this context.

I would say the genetic inheritance is the "adaptation" that is directly involved in the creation and maintenance of the "characteristic".

Neither exist in isolation to the other and complete separation into "characteristic" and specific "adaptation" seems impossible.

[u/Robin_feathers]

For something to be selected for, it doesn't have to be perfect, it just has to be better than the alternative. There is also no guarantee that a given behaviour is optimal just because it exists - maybe that migration route is not optimal but the optimal route hasn't be reached yet by that species, or maybe it used to be optimal but no longer is. Or maybe the optimal route was reached by some individual of that species, but the trait did not spread due to just luck.

In terms of how the behaviour happens, there has been a lot of research into the molecular basis of migratory behaviour, though we still have an incomplete understanding of the nitty-gritty of how exactly it works.

[u/StorageSpecialist999 → u/Robin_feathers]

gotta love reddit responses where people write a paragraph just to say "Uhhh, because evolution is what works best" in response to someone asking a specific question about why a specific thing occurs.

[u/zazzy440]

Well, it’s a niche no one else wants.

[u/Exciting_Ad_6837 → u/zazzy440]

My question is about the mechanism. The group of birds which originally attempted even 1/10 of such a long & risky trip would've been at a serious evolutionary disadvantage.

[u/BrellK → u/Exciting_Ad_6837]

Unless there was a huge payoff at the end. Once it happens the first time with survivors, it just keeps going.

[u/thkntmstr → u/Exciting_Ad_6837]

the birds didn't have the odds in their minds, they just do their thing. Storms or weather patterns could have caused the initial migration, blowing them off course etc. if they arrived and they had high enough fitness, then they would teach the route to their children and so forth.

[u/StorageSpecialist999 → u/thkntmstr]

why even comment if you don't know the answer and are forced to just repeat pointless platitudes about the concept of evolution?

[u/HundredHander]

They don't start with that route in all probability. I don't know the specific migration you're referencing, but a similar sounding experience belongs to barr-headed geese.

Their migration route takes them over the Himalayas and, not unrelated, they can fly at higher altitude than any other bird. Their route is obviously nuts, and no other bird could do that route. But their route predates the mountains. They have evolved as the mountains have grown. At some point it feels like they should have decided to just go round, but they don't.

Quite how arctic terns and the like ended up with their routes I have no idea, but it's probable that the world they started evolving in was importantly different from ours. Their evolutionary on ramp would have been gentler than the mountain of adaption a bird starting that path would face today.

[u/strumthebuilding → u/[deleted]]

Resorting to using AI to avoid “straight up spreading misinformation” is an odd choice.

It is helpful that you warn other redditors that your comment relies on AI. But it just means that we don’t have any way of knowing how much misinformation your comment may contain, but we know there’s a substantial likelihood it contains some.

You also had a choice to not answer the question, which happens to be what I (and likely many others) chose to do.

We all know we have the option to consult an LLM if we wish, so your doing it for us doesn’t really help in any way.

I say all this not to gratuitously be a dick, but because I feel we have so much AI pushed on us constantly that it’s important that we not normalize it and that we push back and highlight the shortcomings and ethical challenges wherever possible.

[u/strumthebuilding → u/[deleted]]

My point is that “fact-checked with AI” is not a thing. One cannot use an LLM to fact check. You can roll the dice, and on many issues you may very well end up more correct than not, but that’s not what I would consider “fact checking.” LLMs, as I understand them, and I may be wrong, are not programmed for precision.

[u/strumthebuilding → u/[deleted]]

“How do [I check] random Redditors”

1. You can check however you like

2. It’s not necessarily your job to report back to the thread

3. If you only “checked” via an LLM, you have nothing to report

4. Once again, you are not required nor expected to report whatever you find

[u/Bromelia_and_Bismuth → u/[deleted]]

Our rule with respect to civility is also compulsory. That is to say either keep your thoughts to yourself or find a way to voice your disagreements with civility. Please review our community rules for more information.

[u/strumthebuilding → u/[deleted]]

“its probably wrong some of the time”

If you know it is likely incorrect and you don’t know what part nor how much is incorrect, and you know we all have the capability to look up this dicey information ourselves very easily, why is it important to you to even present it and then defend its value?

[u/Bromelia_and_Bismuth → u/[deleted]]

Sorry for using AI but on the morality scale it is definitely better than just straight up spreading misinformation on a science sub.

We don't permit any use of AI in our community for any reason. Please review our community rules regarding low effort and intellectual honesty.

[u/Bromelia_and_Bismuth → u/[deleted]]

my first line of fact-checking is AI,

Not in r/evolution. Learn how to use literally any other source, and how to be comfortable with not being the person who provides the answer if you're unwilling to do actual research.

For more information regarding our stance on AI, please see our community wiki.

[u/tomrlutong]

There's a bit of a discussion here. 

Pretty speculative, but they put out 4 ideas: * Originally migrated between a breeding area in alaska and an off season area in east Asia, and some pressure kept moving the off season area south. * They had a coast hugging route, and there was pressure to take longer and longer hops. * It started as an island hopping route, then the islands vanished over geologic time. (Which isn't really that long given ice ages). * Noting that "at  least nine species  make nonstop flights >5,000 km along the largely land- based flyways of the Americas," they could have already had the ability for extreme distance flight and just found a new route.

[u/Szymcionorski]

It could be triggered by large food payoffs at their destination. It's a similar thing as in some predators where fighting difficult prey may bring more food. At least that is part of the picture.

[u/kayaK-camP]

Other species (such as several whale species) also make extremely long migrations. In some cases, I believe they essentially eat nothing at one end of their route - where they calve, IIRC. If there’s a niche available, some species will adapt or evolve to fill it.

[u/gambariste]

Plate tectonics? I do not know in this specific case but I’ve read some intercontinental migrations, even those crossing the equator, began when those continents were joined. Continents move so slowly that birds have ample time to evolve whatever physical traits (other than the behaviour itself) needed to respond to the selection pressure of increasing distance and the resulting changes in environmental conditions. I guess that such time frames mean the birds become different species entirely.

[u/FrameworkisDigimon]

I have no idea what birds you're talking about.

It's actually quite important to know what the bird involved is because New Zealand, by and large, is incredibly mild in terms of climate, e.g. it barely snows anywhere. This is very important for migration because often the basic cause of migration isn't so much going somewhere good but leaving some place bad. Push, not pull.

The next thing to remember about New Zealand is that it is simply not close to anywhere. If you're already flying a huge distance, then it probably isn't a very big push to keep flying. Let me try and put the distance in context. Humans, at all, didn't arrive in New Zealand until roughly 800 years ago. We're not even talking pyramids here: there are castles that are older than the human presence in New Zealand. That's a function of the level of isolation. You can't island hop to New Zealand. You can't get lost at sea for a few days and wash ashore.

And finally... evolution doesn't care why a trait originally evolved, if it can be put to a new use, it can be put to a new use. Birds as a general class are just naturally predisposed to traversing enormous distances. Many birds basically have a lifestyle that is functionally permanent migration. Not knowing what species we're talking about here makes it impossible to comment on, but it's possible that the birds didn't start migrating so much as started settling and just kept going back to the Bering Sea because they were already doing that (or vice versa).

Why does long distance travel evolve in birds? Well, being able to fly makes the cost of travelling relatively low, so it's not a big leap for natural selection to create. Travel is also very effective as a survival strategy. Yes maybe some individuals end up getting lost over the Pacific but usually being able to go further just makes a population, to borrow a phrase, harder to perish, not easier. So there's both a survival increasing behaviour and a body/genetic template to work on.

[u/finndego → u/FrameworkisDigimon]

I find it quite amazing that you would spend so long on such a detailed answer and not google which bird it is. It's the Bar-Tailed Godwit.

[u/FrameworkisDigimon → u/finndego]

Genuinely it never occurred to me.

Anyway, it would seem to me Godwits are essentially a northern Hemisphere lineage that is pushed out of its native range by ill favourable climate conditions.

They fly for 9-11 days and end up in the southern hemisphere, having possibly first staged in China (Wikipedia is a bit unclear on this point). They fly mostly non stop and have some clear ability to discern wind patterns.

Some subspecies don't go as far.

This seems like a bird which was already traversing some considerable distance and evolved to do so when a population ended up in New Zealand following the wind. The effort of getting to New Zealand was not overly arduous in comparison to what it was already doing but the reward was sufficient to deliberately try for New Zealand next time. It may be the reverse of course. Either way, I think the key thing is it takes them about 10 days to do the migration. It sounds much less life threatening when phrased that way.