Friday, November 27, 2009

Otter vs Mink - who's winning?

Carole and I have just got back from a week away at our little cottage tucked away in Lower End, literally on the Bedfordshire/Buckinghamshire border (our front room is in Buckinghamshire and our front door opens on to Bedfordshire!). Frustratingly, I've left the camera/computer lead there, so I'll pop back to get it tomorrow and, hopefully, post something then.

In the meantime, and following on from my last post, there is a fascinating article by Andrew & Lauren Harrington in November's BBC Wildlife magazine exploring the relationship between Otters, Polecats and Mink now that the former two mammals are, once again, on the increase in our countryside - this is certainly true of Bedfordshire.

I love the opening paragraph: 'Like Goldilocks, American Mink moved into an empty house - and ever since they've been breaking the furniture, sleeping in the beds and eating the porridge (well, Water Voles). They've done very well for themselves in Britain. But, over the past few years, the local 'bears' - Otters and Polecats - have started making a comeback. The stage is set for a kind of modern day 'war in the willows' and the battle is on. Or is it?'

Andrew and Lauren are well-placed and well-qualified to comment, working for Oxford University's Wildlife Conservation Research Unit, and having studied Mink on the River Thames at Oxford since 2003.

In recent years there has been encouraging news circulating in various circles involving naturalists and other wildlife enthusiasts, particularly those individuals who have rued the decimation of our Water Vole population. The hopeful talk has been of circumstantial evidence confirming that our returning Otters are, indeed, beginning to displace Mink. But Andrew & Lauren's research seems to suggest otherwise. Although Mink scats are not being encountered as often as in previous years alongside their riverine habitat, healthy Mink are still being trapped as frequently as ever on 'Mink rafts'.

I find the theory as to what is going on fascinating. Let me quote the relevant paragraphs:

'The Mink appeared to be occupying the same waterside real estate, in the same general pattern as before the arrival of Otters, with several non-overlapping female territories being overlapped by that of a single male. They ate a little less fish and a few more birds, but otherwise nothing much seemed to have changed. However, when walking the river by day to search for Mink dens, we came across a Mink swimming.
This was not unusual in itself (though we would have expected the nocturnal Mink to be sleeping). Mink are as adaptable in their habits as in habitat. But it became more noteworthy when our teams of volunteers went out at night wielding radio transmitters and antennae, all set to track several Mink that had been fitted with tiny radio-transmitters on collars, only to find them all sleeping, safely tucked up in their dens.
We followed our Mink intently, around the clock, and confirmed that they were now sleeping at night, but active in the middle of the day. Curious, we dug through old files to find radio-tracking data from the 1990s, before the Otters had returned, and discovered that in those days Mink behaved as expected: they were active at night (generally for only a couple of hours) and mostly slept during the day. It would seem that our Mink have changed their activity patterns to avoid the large nocturnal Otters...The strange disappearance of the Mink scats may simply mean that the Mink are less keen to advertise their presence now.'

It may be that the Mink are avoiding the nocturnal Polecat, too, and it has been noted that Mink today are on average 100-200g lighter than those caught and examined in the 1990s, which could be a result of the new challenges they're facing in the face of the return of our Otters and Polecats.

The article concludes, ' the intensely farmed landscape of southern England, where Mink are confined to narrow strips of riverside habitat, it is harder to avoid competitors, and so other strategies may be necessary for them to live side by side with their relatives. it is also possible that more subtle effects, such as decreased body weight or increased stress, may cause a decline in Mink numbers in the longer term.
This, as you can probably see, is only the beginning of the story. A field biologist's job is never done - only time will tell what will happen on our rivers over the next decade.'

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