It’s not an unreasonable question. The western coast of Wales has a mild and relatively equable climate in winter – although rather damp – and there are plenty of rivers, lakes and estuaries where they could find fish, right?
Not exactly…
The coastal ospreys prey on species such as mullet, flounder, brown trout and the occasional sea bass. All of these fish are migratory in their season: mullet move south and/or east in November, and by late December almost all of the adult flounders around the Irish Sea margins have disappeared – though exactly where they go is something of a mystery.
And the current pattern of mild off-season weather was not always so. In the 16h and 17th centuries – a period known as the “little ice age”- many rivers and inland waters, and even parts of the sea, froze over in successive winters – a potential disaster for birds that eat nothing but fish.
As a behaviour, avian migration may be almost as old as birds themselves. [Alerstam 1990] Scientists still argue about how it first evolved, but there is little doubt that the ability to “move home” in response to changes in the environment or food supply has been a secret of survival for many species. Current theory [Berthold 1999] is that almost ALL bird species have the potential to migrate, whether they actually do so or not.
So it is with European ospreys: over millennia, they have developed a selection of routes and destinations which – taken over all – have given them the best chance of breeding success. By returning to Africa after breeding here, they eliminate the risks of cold or hunger – a balance of benefit that must outweigh the hazards of migration itself.
The life-cycle of the osprey spans years and crosses continents. It is part of what they are, and so the osprey is not a Welsh bird any more than it is an African bird. They are birds of the world, global travellers in deep time, and out of that time they will return again…
… next year.
Paul Wildlifewriter