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What would cause the temporary migration of a carnivore/scavenger avian species, normally inhabiting a temperate to tropical region, to a much colder one.

It's a seasonal migration, but also a rare one happening only in the colder winters.

They usually inhabit a large archipelago near my planet's equator, in the southern region of it since the equatorial zone is the middle of the ocean.

They are a type of flightless vulture as large as ostriches and as intelligent as parrots/crows.

They would have to run/walk over ice across islands to reach the continent, they are very fast, like ostriches. The path would only be possible in deepest winter and only very rarely.

It's unknown if by accident "humans" taught them the way or if they were just curious.

That's what I'm trying to determine. I know crows and parrots can learn things not natural to them, but would they act against instinct to satisfy curiosity? Or would they have to be pushed by something else.

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    $\begingroup$ Many birds make these exact migration. Whooping cranes travel from florida to minnesota every year. Carnivorous shouldn't apply. How fast do they travel? That seems like the only hurdle you have. $\endgroup$
    – SFWriter
    Sep 22, 2017 at 15:25
  • $\begingroup$ Something you should clarify: do you mean a seasonal migration every year? Or do you mean some sort of semi-permanent (multi-year) movement to a new habitat due to (insert reason here)? $\endgroup$
    – Palarran
    Sep 22, 2017 at 15:30
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    $\begingroup$ @Raditz_35 they would have to run/walk over ice across islands to reach the continent, they are very fast, like ostriches. The path would only be possible in deep winter and only very rarely. It's unknown if by accident "humans" taught them the way or if they were just curious. That's what I'm trying to determine. I know crows and parrots can learn things not natural to them, but would they act against instinct to satisfy curiosity? Or would they have to be pushed by something else. $\endgroup$ Sep 22, 2017 at 16:13
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    $\begingroup$ I would think the tricky part is getting them back to their island before the breakup of the ice bridge. If they can handle the mainland at it's most inhospitable why bother with an island? $\endgroup$
    – user25818
    Sep 22, 2017 at 17:14
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    $\begingroup$ @Starty the migrations would happen every century with regularity, and also during other occasionally colder winters. My doubt is if simple curiosity would be enough to get such animals to migrate, if curiosity would suffice or if something else would have to be the cause for a migration of this type. Would they give in to curiosity over instinct as some animals do. Or should I use the threat of hunger, or a learned behavior instead. Or maybe a combination of everything... would a crow or a parrot go near something they should fear just out of curiosity? $\endgroup$ Sep 22, 2017 at 17:37

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They are a top predator on their islands and the adults can reliably handle everything active during winter on the mainland, but sumer is coming.

Running across ice is easy for them, and they can prey on abundant mainland and semi-aquatic animals with less efficient ice locomotion. Getting off their islands is as easy as following the seals' air holes.

On the mainland an extra harsh winter is a heyday for a carrion eater.

But then comes spring. Before the ice breaks up mainland predatory hibernators wake up and are more than a match for these birds. The birds flee to their islands to breed safely.

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  • $\begingroup$ Brilliant! Have to introduce them to the terrible nearbears/halflions. $\endgroup$ Sep 22, 2017 at 18:17
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You have specified that they do this somewhat periodically (but not often enough to proclaim the cold climate zone a mating/breeding ground) and that the way there is rather easy and not such an obstacle. How they get food on the way is maybe another question. For them to migrate every once in a while, there needs to be an advantage. One could imagine a symbiosis with some species, but I guess that's rather hard with such birds. So let's assume a food source.

There are cicades that show up every couple of years. In your cold region, there might be a similar animal (let's call it A) that only shows up under some conditions. Your carnivores might really, really like eating A. So when it's A season, the species migrates to where they can get A.

I think the main advantage with this approach is that the birds migrate to a specific area and do not just go anywhere and it is somewhat grounded in reality.

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They are forced out.

If this happens very rarely, individual animals will not be aware of anything they want on the mainland. They would not go. Also if they did go they would likely be stuck since never having done it before they would not know that the bridges would disappear.

Your birds do not want to leave the island but they do only in dire need, and they return as soon as it is possible. The rare ultra cold process that opens the ice bridges also produces some phenomenon on the island that they must flee from. This rare and fearful process subsides before the ice bridge melts. This means the birds would flee only as far as they need to to escape this process, and start moving back as it subsides.

What could this dread ultra cold process be?

Carbon dioxide snow?

Intolerably squeaky squeaking snow?

Too damn cold for birds?

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