But Which One?
Here’s the story. It’s about a juvenile harrier that did a once fly-past at Spurn, East Yorkshire on 28th August 2010.
Mystery Photograph: Identify the species. Answer next month! (any one else remember regularly reading those enticing words?). Flying over shorebirds on the Humber and Spurn’s ‘Narrow Neck’ in the background.
A juvenile Harrier sp. passes through Spurn’s triangle zone and out across the Humber. Watched for not more than handful of minutes by about 30 observers and never close. What would you have called it?
It was a Montagu’s Harrier, maybe a Pallid Harrier, a Hen Harrier and an (American) Marsh Hawk depending on how well you saw it!
Here’s the story:
The following photo was taken by my daughter Abigail, as we were walking back towards the Bluebell. Leaden skies appeared to the south. Before long large rain drops necessitated a quick dash to the cafe. Pete Wragg joined my family around the table and just as we settled in for welcome victuals, our radios crackled. The same rain that caused us to seek shelter had ‘forced down’ a large raptor. A sleek handed, orangy looking bird-of-prey had flashed past the caravan of one sharp-eyed birder- possibly Montagu’s!
Pete and I grabbed bins and ran out to suitable vantage point. Scanning the fields near the Warren the bird rose up having alighted briefly. “There it is!” Except to me it looked too broad-winged for a super slim Monty’s (eek… perhaps Pallid), which I hesitantly mentioned to Pete. Some 30 birders emerged from sheltered locations as the bird disappeared from our view. Pete and I headed towards the road seeking another vantage. I had no more views. Others watched as it flew alongside the canal zone and very soon, out towards Lincolnshire. Ian Smith managed a handful of distant shots.
So what was it?
Post-sighting analysis: The bird’s identity was briefly discussed. Some were thinking it looked OK for a Montagu’s Harrier. A couple of us felt it too-broad winged, which is why I even contemplated the bulkier Pallid. The answer lay in Ian Smith’s photos.
Hmm. What if there had been no photos? What species would have gone down in birders notebooks/ on the internet/ in the evening log at Spurn? The photos above and below show the wing formula of a Hen Harrier. This was not noted as it passed rapidly by. Indeed, flying into strong winds caused the wing tips to be sometimes sleeked back and appear narrow. It was rather plain and orangey looking according to some observers. In these photos it also looks dark-hooded. And the outer primaries appear to have lots of bars- don’t they? As I looked through Ian’s photos on his computer screen – this question came to mind. ”Why is it not a Marsh Hawk?”. The North American Hen Harrier. Some features on these slightly blurry photos look good for a ‘hudsonius’.
Fortunately Ian photographed a juvenile Hen Harrier exactly one week earlier at the same place- indeed flushed from the same field as the 28th August bird. This one can be more easily identified as a juvenile (Eurasian) Hen Harrier. Actually I would argue, the way some large birds move up and down Spurn – it could even be the same bird!
Certainly pretty dark looking ‘plain chocolate’ above - sometimes a quoted feature of ‘Marsh Hawk’. Wing tip appearance of harriers can vary in the field, in photos and even on the same individual (see above).
juvenile Hen Harrier, Clubley’s Field, Spurn 21st August 2010, Ian Smith. Juveniles with a orangey underparts are not unusual. Some juvenile Marsh Hawks can come quite close in general appearance to this. On the finer details, this bird show 3 bars on the outermost long primary and 5 bars each on those 2 long primaries next to it. You would want one more bar each of those (4 and 6 respectively) to claim a Marsh Hawk.
juvenile Hen Harrier, Clubley’s Field, Spurn 21st August 2010, Ian Smith. Count the bars again if you like. Also note the 3 dark bars (including the dark trailing edge) in the middle part of the underwing. Ideally a Marsh Hawk would have a narrower central bar. The trailing edge of the inner primaries is obvious dark and the dark shaft streaks on the undertail coverts caught my eye. Do Marsh Hawks ever show these?
juvenile Marsh Hawk, Connecticut, December, Julian Hough.
Here’s a real Marsh Hawk. Maybe a juv. male (the iris looks like it might be pale). Count the bars. Just about visible – 4 on the outermost long primary and 6 on the next 2 (look carefully). It also has a slightly more solid dark ‘boa’ – the area behind that speckled pale thin collar, slightly weaker streaking on the breast and no dark shaft streaks on the undertail coverts. The central dark bar on the secondaries is obviously thinner and trailing edge of the inner primaries looks rather pale. The undertail coverts have no dark shaft streak. All subtle stuff. Which is why…
I learnt lots from this experience like:
- always beware of once-seen fly-by rare bird claims. Mistakes are common!
- blurry, distant photos won’t do when subtle features need to be seen
- while some juvenile Marsh Hawks are very distinctive, others will be very hard to identify unless seen/ photographed very well!
I chatted about this stuff with John Martin, Julian Hough and Alex Lees. Some comments:
from John Martin:
“As you say, the 28th August Spurn bird is clearly a Hen type on wing formula and could easily be the bird from 21st, which is presumably a juvenile Hen as it’s in Yorkshire in August. Both quite orange bodied but well within normal variation of juv Hen. The photos of the bird on 28th are way too poor to even think about a hudsonius claim on a bird like this – you just can’t see it well enough and with poor views streaky hoods can look solid, streaked underparts can look unstreaked etc – beware, this is crucial but perhaps not emphasised enough in the paper. The bird on 21st shows too much streaking and too streaky a dusky hood but you could get some poorly marked Northerns (Marsh Hawk) like this. Julian’s does show finer streaking more confined to flanks and close to the more solid hood. They can be tricky and you need decent photos. For some birds you probably can’t do them. Others however are really striking and don’t require quite such detailed images to nail them.”
from Julian Hough:
“I think it’s downright tough to nail one based on the plumage variation and overlap in many characters – without considering hybrids. The characters of juvenile Marsh Hawk from my experience:
- variable in underpart streaking – some basically unstreaked, some with breast band of streaks across breast and down flanks.
- boa variable in darkness, but typically giving hooded effect
- leading edge of underwing coverts usually unmarked and buffish and undertail coverts and lateral tail coverts unstreaked (typically streaked in Hen – not sure how reliable this is
- bands on P8 variable but as mentioned by you, typically 5-7 in hudsonius
- upperwing coverts and tail sides with warm rufousy edgings
- white at rear of eye often broken by post-ocular eyestripe, but this is matched by other harrier sp
- paler trailing edge to inner primaries
Basically all the features above are variable and seem to be matched by some cyaneus (see Spurn bird) which would likely be unidentifiable in the field. Birds in areas that have proven capacity for American vagrants (Scilly/Shetland/Cornwall) and where harriers are uncommon might indicate a better probability, but without close photos, identification will not be easily proven. Birds in late September -November also increase the probability as opposed to birds in August which stand a good chance or originating from more local populations.
I have definitely changed my thinking in the light of researching images and looking at individuals such as the Spurn bird to think that in most cases proving the occurrence of a hudsonius (even with photos) beyond reasonable doubt is probably an uphill battle. The Spurn bird wouldn’t get a second glance here in the US as a possible cyaneus since the characters are so close to hudsonius.”