Monday, 23 January 2012

Wrong side of the river

Tale of the unexpected: an American Mink is mobbed as it breaks cover in Thamesmead, south-east London.
I made a rare trip across the Thames to ‘sarf’ London today, mainly with the aim of seeing the second-winter Iceland Gull at Crayford after a tip-off from Kev Jarvis. In that ambition I failed, the gull departing before I arrived on site. A fly-by first-winter Yellow-legged Gull was scant consolation, but having then heard from Kev that Rich Bonser’s Ferruginous Duck at Thamesmead had been seen again, I duly set off in pursuit.

It’s been some time since I navigated my way around the back streets of Thamesmead, as a result of which I eventually ended up at Thamesmere Lake East. There was no sign of the Ferruginous Duck, a fact that became less surprising when John Archer helpfully tipped me off that it actually frequented Thamesmere Lake West. While at the east lake, however, I caught sight of a small animal scurrying along the far bank of the lake. Getting the bins on it, I quickly realised it was an American Mink – a species I haven’t seen in the wild previously in Britain.

This introduced predator is a serious problem for breeding waterbirds and small mammals.
The mink forages along the lake bank before disappearing in dense vegetation.
As the mink broke cover and ran along a concrete wall, Black-headed Gulls and Carrion Crows immediately gathered to mob it. The creature foraged briefly along the lake bank before disappearing into deep vegetation. While pleasing to see something unexpected, it was at the same time alarming – American Mink are voracious predators, their presence often being associated with catastrophic declines among Water Vole populations and damaging impacts on gull and tern colonies, even on offshore islands.

Interestingly, it is the second sighting of this species along the Thames in London this month, Dave Morrison having photographed a different mink at Beckton Works just across the river. Hopefully, measures will be put in place to control this introduced predator, or the consequences for local wildlife could be severe. 

White-fronted Geese in the Ingrebourne Valley.
After that distraction I arrived late at the neighbouring lake, with the Ferruginous Duck having now retreated out of view into the reeds (as it apparently likes to do). My first Common Chiffchaff of the year and a couple of calling Water Rails were the only notable species, so I headed back to Crayford, failed again with the Iceland Gull (though this time had second-winter and adult Yellow-legged Gulls) and cut my losses by heading north through the tunnel. Saving the day bird-wise were two White-fronted Geese in the Ingrebourne Valley, always a good species to see in London (thanks to Dave Mo for the tip-off).

* Footnote: researching American Mink subsequently, I was amazed to learn that one recent estimate put the British population at 110,000 (England 46,750, Scotland 52,250 and Wales 9,750 – Mammals of the British Isles by Harris and Yalden, 2008). I don’t know the species’ status in London – comments welcome.

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