Saturday, 8 July 2017

Instrumental Solo

Why don't ospreys migrate together as a family unit?” It has almost assumed the status of Frequently Asked Question, and the answer is simple...
It's because they're ospreys...

Some other species of birds, for example geese and wild swans, do exactly this: they travel from their breeding sites in family groups, with the adults escorting their offspring to the wintering grounds, hundreds or even thousands of miles distant. Without this guidance, the fledglings would never know where to go. But in evolutionary terms, the logistics of this have a very specific result: in a given population and after only a few generations, all the birds end up wintering in the same place! For grazing birds, this is a perfect survival strategy. They assemble in a huge flock, food is not a problem, (grass doesn't run away or hide) and there is safety in numbers with many eyes watching for danger.

But for ospreys and other species that hunt a limited resource, this system won't do at all. They are apex predators, not flocking geese...

A thousand ospreys arriving on a single African lake would exploit the local fish supply at an unsustainable rate. To solve this problem, evolution has arranged matters so that young ospreys have to find their own way in Autumn. They are born with all the navigational instincts needed to do this, but built into those same instincts is sufficient positional uncertainty to ensure that the young birds are dispersed over a wide wintering area. 


This random end-point factor (referred to by scientists as a “stochastic element”) is one of the hidden secrets of osprey migration and is instrumental in forming many aspects of their post-juvenile behaviour.. It has evolved because a general dispersal in winter quarters gives the incoming youngsters a slightly better chance of survival as individuals. 


But where does this "randomness" in the selection of a final destination come from?  That's a whole other story and really needs an article all of its own.

Watch this space... ☺

4 comments:

  1. That is very well explained.

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  2. Thanks Paul.

    The basic common sense of their world - why can't we behave like that.

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  3. Very interesting. Thank you Paul this helps when asked at the DOP.

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