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Even birds need some winter sun!


Image by Vincent van Zalinge


Today, May 8th, is World Migratory Bird Day. How exciting! To celebrate, we'd love it if you could join us for a mini-lesson in migration! Remember, this is a massive topic, so we're only going to be covering the broad strokes. If a written form isn't your favourite thing, no worries - we'll have a YouTube video up soon for those who are better auditory learners!


Just as a refresher, migration can be defined as the ‘regular, long-distance movement of animals from one location to another’. Of course, many birds migrate seasonally – we’ve all heard of ‘flying South for the winter’! – but the question is why? Migration is incredibly energetically costly and is full of risks (the risk of starvation, getting lost, predation, exhaustion...), so why bother at all?



WHAT’S THE POINT?

An obvious reason is to avoid adverse conditions – bad weather, for example, and harsh winters. Many birds will migrate elsewhere, both to avoid inhospitable conditions and to ensure adequate food supplies in an alternative location. Fluctuations in the climate may lead to food sources only being available seasonally, meaning some birds must leave to find food elsewhere.


Migration can also enhance reproduction, which is really the ‘Big Thing’ in nature! Migration can even occur to decrease competition between species and conspecifics (individuals of the same species). There are so many reasons why some animals migrate!



CLASSIFICATION OF MIGRATORY ANIMALS

Did you know that we can classify different types of migrants, too, based on distance, reliance, and circumstance?


DISTANCE

Migratory animals are typically divided into four ‘distances’ – resident, short-distance, medium-distance and long-distance. The names are pretty self-explanatory, but let's go ahead and provide a bit of context.


RESIDENT

A resident species is a species that remains in one geographical region for the duration of its life. We know, we know, this one is kind of cheating - it isn’t a migrant if it just stays home!


SHORT-DISTANCE

An example of short-distance migration is altitudinal migration! This is when a population moves seasonally from one elevation to another, and could occur for a number of different reasons, including access to nesting sites, in response to changing weather conditions and even as a response to anthropogenic factors (factors caused by human activity).


MEDIUM-DISTANCE

An example of a species that undertakes medium-distance migration would be the Killdeer (Charadrius vociferus). This species lives in the United States and Canada. Keen birders have noted that Canadian populations tend to venture south for the winter, but only as far as the South-Atlantic states. For this reason, they are not considered long-distance migrants.


LONG-DISTANCE

Long-distance migrants include the European pied flycatcher (Ficedula hypoleuca), which flies from where it breeds in Europe and Asia, all the way to Africa, where it winters! Long-distance migrants require 'stopover sites' in order to eat, drink and rest before they continue on their journey. Without these stopover sites, the birds would sadly not survive the trip. It is therefore essential for conservationists to understand the movements of long-distance migrants, including their chosen stopover sites, as these sites must be preserved in order to protect the migratory species. Such protections, of course, require international cooperation and thus can be difficult, delicate matters.



RELIANCE

The terms ‘facultative’ and ‘obligate’ come up a lot in wildlife biology! Migrants can be either of these things.

OBLIGATE MIGRANT

These are migrants that are obligated to migrate for their survival. Their migrations are generally cyclical and occur in response to predictable variations in their environment (for example, the changing seasons). Direction, timing and duration of the migration are relatively consistent year after year.

FACULTATIVE MIGRANT

These are species that are considered to have the 'option' to migrate. They tend to do so less predictably; it depends on the conditions at the time. Some years they may migrate, other years they might not. It is not 'hard-wired' in them the way it is in obligate migrants.


CIRCUMSTANCE

Individual migration can be accidental or non-accidental. Non-accidental (so, deliberate) migration can be either calculated or non-calculated. In non-calculated migration, the risks and benefits are unknown to the animal - thus, most non-calculated migration is exploratory. In comparison, in calculated migration, the risks and benefits are known. Return trips, then, are calculated.


Non-accidental migration should only occur when doing so increases the reproductive benefit to the animal – basically, the benefits of migrating must outweigh the costs.


PHEW!

That was a slightly longer one, wasn’t it?


Migration is a HUGE topic, and there is so much left to talk about that we didn’t cover – multi-generational migration, complete vs partial migration, zugunruhe… the list goes on! But if we kept writing, this would be a book, not a blog post!


Also, while we've focused on migratory birds this time, many other animals migrate too - from wildebeest to eels, from butterflies to reindeer - the list goes on! Keep your eyes peeled, because we'd love to talk about these other migratory animals in a future post.


Thanks so much for joining us to learn more about migration! We hope you’re armed with some more knowledge now and have come away with a few fun facts!

Thanks again for reading, and remember to always keep learning!


-- Charlie and Tiana

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