A visit to see a controversial Canvasback and thoughts on its provenance

  

Canvasback ( its the one with the long black beak) curtsey of Nick Truby

 

Ornamental ducks are perhaps the most difficult and controversial birds that are on the current  British bird list. They are widely kept in collections and as such differentiating a genuine wild vagrant from an escapee is extremely challenging and sometimes impossible. I’ve discussed the issue of proving a birds provenance before, see here, but in summary a ring or isotopic analysis of a sample are required to prove beyond all doubt that the bird is a genuine vagrant. In the absence of this objective evidence of origin much more subjective factors are used to prove that the bird is “probably” a genuine wild bird. You could, however,  strongly argue that in the absence of the definitive evidence above, none of these ornamental ducks should be on the UK list of accepted wild birds

 

The Canvasback is the North American cousin of our common Pochard and is kept in some UK ornamental duck collections. It is, however,  rightly or wrongly on the BBRC British bird list with 7 records accepted based purely on subjective factors. 

 

When a Canvasback was found associating with a large flock of Common Pochard at Abberton Reservoir in Essex some 10 days ago I was in two minds as to whether or not to visit. Arguing perhaps in its favour as a genuine vagrant, there are two previous records from this site  involving long staying birds in 1999 and 2000. These were arguably drawn in by the presence of an exceptionally large flock of overwintering Common Pochard. What weights against it is the fact that they are kept in captivity in the UK.  In fact 6 captive birds were released at Flixton gravel pits in 2020 only 50 miles away from Abberton. I did try and qualify how many are kept in Uk collections but this information does not appear to be  readily available. There are, however, a number of sites in the UK offering captive breed birds for sale. The Flixton birds, however, are allegedly pinioned, a surgical procedure to render the bird permanently incapable of flight. But I guess it’s not inconceivable that they have bred and their offspring have dispersed. 

 

I’ve had a few visits to hospital in the past month or so for various tests and procedures to try and diagnose a health issue with some concern it could be something nasty. After the last procedure on Tuesday it was diagnosed as something not too serious or life threatening so I decided to celebrate with a  day out birding on Wednesday  by paying a visit to Abberton reservoir for what I guess you might call an insurance tick of the Canvasback. After a stressful day on Tuesday at the hospital I really did not feel like getting up early so it was almost midday when I finally arrived on site in Essex. With the very short winter days upon us this meant that a 7 hour round drive was going to yield just 3 and a bit hours of good day light for birding. Not a great ROI I must say but, then again, I’m not renown amongst family and friends for my common-sense!

 

I have never been to this site before but followed the RBA instructions to park and view the reservoir from a long causeway. Another birder was just leaving and he told me that it had taken him 2 hours to locate the Canvasback in amongst the Common Pochard. When I looked over the reservoir I could see why, there must have been several hundred Common Pochard on the water, by far the most I have ever seen in one flock. The flock was initially clustered quite densely in the corner of the reservoir to the left of me and another birder very kindly allowed me to look through his scope at the Canvasback.

 

The Canvasback is the largest diving duck in North America and is very widespread. It breeds in Canada and the northern USA migrating to the southern USA for the winter. It shares many features with our Common Pochard with a chestnut red head and neck, a black breast, a greyish back, black rump, and a blackish brown tail. The drake's sides, back, and belly are white with fine vermiculation resembling the weave of a canvas, which gave rise to the bird's common name. It differs from our Common Pochard in that it has a long prominent black bill with none of the slatey grey bands always present on adult drake Common Pochard. It is also noticeably larger when seen well next to its european cousin.

 

I managed to get it in my scope a couple more times before the majority of the flock drifted off distantly into the middle of the reservoir. I spent the next couple of hours trying to locate it again in the scope, dismissing hundreds of Common Pochard in the process. The flock was densely packed with maybe 50% asleep with their heads tucked in and I could not re-find it. By 15:00 the light was going making it all the more impossible to scope the flock and I decided to cut my losses and leave with my insurance tick but no photos. I’m hence indebted to my good friend Nick who visited last weekend and got all the excellent photos on this blog.

 

I’m calling this an insurance tick on the basis that it might get accepted by the BBRC. I’m in two minds as to whether to add it to my UK list before BBRC rule on it – perhaps I should include it as half a tick!

 

 

Footnote - My blogs are posted with sometimes rather imaginative spelling and grammar due to my extreme dyslexia!