A tale of nature, wildlife and birding from Cheshire, North Wales and across the globe....

A tale of nature, wildlife and birding from Cheshire, North Wales and across the globe....

Tuesday, 1 March 2016

Hooded Merganser - Corsham Lake, Wiltshire - will it get accepted on to Category A?

With the Hooded Merganser at Corsham Lake in Wiltshire presenting a tempting opportunity having never seen this species before, even in America, on Saturday I made the 3 hour journey down south so me and Alex could decide for ourselves just how genuine a vagrant this particular individual was.

Having been present at the lake in the grounds of Corsham Court since the Monday, we arrived just after lunch and squelched our way through the mud to the water’s edge. Scanning the lake, we could see several Mallards and 4 Goosanders resting on the opposite bank, as well as numerous other ducks out on the water, but no sign of the Hooded Merganser –  surely we couldn’t dip a potential escapee (the shame!).

Speaking to the birders present with scopes already lined up and cameras poised at the ready, it transpired the bird had simply moved left down a channel behind the reeds and was busy feeding temporarily out of sight. Reassured, we headed that way, and soon managed to lock on to it – constantly diving in the shallow water and taking advantage of the apparent rich source of food amongst the reeds. Success! One Hooded Merganser showing exceptionally well….. perhaps a little too well?!
Hooded Merganser - Corsham Park, Wiltshire
Watching the bird for the next hour, we obtained excellent views as it fished in front of us, at one point coming to within just a few metres. Expertly manoeuvring through the channel, it often came to a patch of open water not obscured by any branches or reeds, offering a great opportunity to really take in the oversized head and fluffy crest during the moments that it surfaced.
Hooded Merganser - Corsham Park, Wiltshire
Hooded Merganser - Corsham Lake, Wiltshire
So, was the Hooded Merganser getting just a little bit too close for comfort? Usually when vagrant wildfowl are extremely confiding it can often be a sign that they have escaped from captivity, in many cases resulting in the individual not getting accepted or instead, getting placed firmly on the dreaded Category E of the British list. Indeed, Cinnamon Teals, Mottled Ducks and even White-headed Ducks have all met this fate in Britain, having never made it on to category A and instead getting resigned to the depths of categories D and E. As captive wildfowl are extremely numerous in Britain with birds often escaping, such records should always be treated with caution.
White-headed Ducks - Spain
White-headed Ducks - sadly resigned to Category E of the British list despite many candidates
Hooded Mergansers have always had a troubled journey when it comes to getting accepted on to Category A of the British list – it wasn’t until 2008 after careful scrutiny and consideration that the first was accepted – a female or immature male present on North Uist from the 23rd October to the 1st November 2000 (a whole 8 years after the sighting). Since then, 7 records in total have been accepted.

In general, certain points always need to be considered when assessing whether a species of bird that is often kept in captivity is indeed a genuinely wild vagrant. As well as the obvious essential features such as being unringed and having unclipped wings, the bird’s wariness of people is a key indicator, as is its behaviour in terms of feeding – natural sources are a yes while coming to bread (in terms of wildfowl) is often seen as a no go. The Corsham Hooded Merganser has been seen to be unringed on both legs, often displaying its legs to observers whilst preening and at some points even coming completely out of the water and on to the bank – clearly displaying a lack of rings. The wings also appear to be unclipped.
Hooded Merganser - Corsham Lake, Wiltshire
No bling!
Its apparent tameness however could prove to be an issue. Whilst the Hooded Merganser was indeed seemingly unperturbed by the 10 or so birders lining the bank, it should be noted that it was extremely focused on hunting for fish and other morsels in the shallows. One interesting theory in particular is that when the Mallards swam close to the bank, they disturbed the sediment in the water and this in turn made it easier for the Hooded Merganser to catch larvae and other invertebrates that were disturbed by the movement.

Another point to consider is that over in America where Hooded Mergansers are native, they often come to within a few feet of people, sometimes even taking bread or other food - as the three videos below demonstrate perfectly. 

The Corsham bird’s apparent tameness is therefore certainly no reason to cast any doubt over its wild credentials. Whilst it has been reported to have been feeding on bread on some occasions, Goosanders have also been observed to do this in the wild, and it would make sense for any wild bird to take advantage of whatever food source is offered.

Other key points that need to be assessed in the case for genuine vagrancy is the bird in question arriving at the right time of year to tie in with natural migration, as well as departing in good time to continue with its journey. Whilst the Radipole male in Dorset apparently arrived during fierce storms that battered the south coast, the fact that it has not moved on since and is still present 8 years later completely destroyed its case as a true vagrant, as did the fact that it arrived in June.

With the Hooded Merganser at Corsham Lake having now departed after a stay of just 6 days (whilst we were there it was constantly diving for food – perhaps feeding up before moving on), this can only strengthen the argument of it being a wild bird.
Hooded  Merganser - Corsham Lake, Wiltshire
Turning up in February is also a positive point for the Corsham bird, as wild Hooded Mergansers in America are very early spring migrants, leaving their wintering grounds in February and March. This winter saw huge Atlantic pressure systems bringing many American wildfowl species across, with numerous Green-winged Teals, American Wigeons, Lesser Scaups and Ring-necked Ducks all present in good numbers in the UK. 
Ring-necked Duck - Priorslee Lake
Ring-necked Ducks and Lesser Scaups all regularly make it over to the UK
Lesser Scaup - Marshside RSPB
With several records of Hooded Mergansers in the Western Pal this winter, including presumed wild individuals in both the Azores and Iceland, as well as other vagrants such as American Coots, it is highly likely that the Corsham bird could have been blown over the Atlantic during the extreme weather conditions seen in November and December when the winds originated strongly from North America, arriving elsewhere on the continent before the urge to move on kicked in.

It's also worth noting that the female reported in Forth in Scotland back on the 2nd February for two days could well be the Corsham bird. First seen on the pond at the Safari Park in Blair Drummond, it is essential however that an escapee from there is eliminated first and foremost. Escapees from any centres nearby to both the Forth site and the site in Wiltshire will then also have to be ruled out for the Corsham bird to have any chance of being accepted.

Whilst the fate of the Corsham Hooded Merganser is uncertain, regardless of whether or not it is accepted it was still a fantastic bird to watch and to get such good views of. I’ll certainly be keeping my fingers crossed that it does indeed tick all the required boxes of being wild and earns a place on to category A.

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