April Highlights and that Chiffchaff...

Black-necked Grebe Grimsbury Reservoir courtesy of Richard Tyler.

Following March's slightly unusual mix in Oxfordshire of notable birds more closely associated with winter, it was a return mainly to regular fayre through the peak passage month of April. All the expected migrants are now with us, some a little late, a few seen in new and different places; and various of them offering good picture opportunities.

Bird of the month was probably the atypical Chiffchaff at Hinksey Heights, Oxford mid-April, for the interest and excitement it created. Ticked initially by many Oxon county listers as an Iberian Chiffchaff, it sadly turned out not to be one after due analysis was applied. Our esteemed county bird recorder explains all in the article that follows this summary.

The "Iberian" Chiffchaff, courtesy of Roger Wyatt

Running that mystery warbler a close second must be the gorgeous Black-necked Grebe that graced Grimsbury Reservoir, Banbury on 12th and 13th. It has been a good year so far for this scarcer grebe in the county, but the latest individual was the first in full breeding plumage and so drew many admirers.

Perhaps April's scarcest sighting was a Red-throated Diver, spotted very briefly at Farmoor Reservoir on 2nd. Two Great Skua were a further headliner there for a couple of hours on 28th. A lone Pink-footed Goose was found amongst the feral flock on Port Meadow on 29th.

courtesy of Nick Truby

In between, drake Garganey settled briefly at Farmoor again (13th) and Otmoor (16th). A Sandwich Tern was photographed fishing the Thames in Port Meadow (18th).

courtesy of Roger Wyatt

My personal favourite April picture is this Cuckoo (below) at Farmoor on 16th. That iconic herald of approaching summer was also noted from various other locations county-wide.

courtesy of John Workman

 Yellow Wagtail as usual were popular draws for our own and visiting snappers, being brightly coloured. As in recent years those at Farmoor included a pale blue-headed Channel Wagtail (M.f.flavissima x M.f.flava) that generated much attention. More unusually, the hybrid was preceded by a pure Blue-headed Wagtail pictured there on the evening of 12th.

Blue-headed Wagtail, courtesy of Dai John

Yellow Wagtail, courtesy of Mark Chivers

"Channel" Wagtail, courtesy of Ewan Urquhart

Also at Farmoor a Black Redstart was active around the water treatment buildings on 9th and 10th. Transient Common Redstart were reported by sharp-eyed observers from a good spread of Oxon locations, even a garden in Abingdon (18th).

Black Redstart, courtesy of Badger

Common Redstart, courtesy of Paul Wren

Passage Ring Ouzel were first found on 3rd at their traditional hot spot Linky Down on the Chilterns escarpment, and were seen there regularly over several more days. More mid-month occurrences of this smart upland thrush came from four other places, with a later one at Lark Hill, Wantage at month's end. Northern Wheatear were seen throughout April, and 2018's first Whinchat record came from Lollingdon Hill on 20th.

Wheatear, courtesy of Nick Truby

Further passerines of note included a Wood Warbler present at Grimsbury Reservoir on the morning of 20th, singing intermittently and showing well at times. A Pied Flycatcher was viewed briefly from the bridleway at Otmoor the following day, while the year's first Spotted Flycatcher records came from the Trap Grounds by Port Meadow (27th) and LWV Pit 60 (29th). Tree Pipit were noted twice in the south of the county.

Wood Warbler, courtesy of John Friendship-Taylor

Up to 3 Grasshopper Warbler were heard reeling around Shrike Meadow, Farmoor on 22nd and subsequently. That species was also amongst the usual array of warblers returning to RSPB Otmoor, while another was logged close by Grimsbury Reservoir on 18th.

Grasshopper Warbler, courtesy of Jeremy Dexter

By month's end 10 warbler species were being  observed or heard on Otmoor on any day, as is customary for this time of year. In the absence of scarcer migrants at Farmoor, the reservoir's regular watchers recorded a comparable array of newly arrived warblers there as well. That must bear testimony in part to the recent and very welcome restoration works at the site's Thames-side nature reserves.

Sdege Wrabler, courtesy of Terry Sherlock

Where seasonal raptors are concerned, later northbound Osprey flew over Balscote Quarry (3rd) and Standlake (16th). The ever popular Hobbies returned to Otmoor from 20th and more were seen around the county.

Hobby courtesy of Nick Truby

On some different notes, a booming Bittern was heard at Otmoor on 21st. A late Short-eared Owl report came from the RSPB reserve on 14th, with another at Balscote Quarry on 19th. An errant Shag zipped through Grimsbury Reservoir after a squall on 25th.

Standing out amongst the month's passage waders were 2 Knot at Farmoor (8th), 4 Avocet at Dorchester GPs (11th), a Grey Plover at Farmoor (21st) and Whimbrel through Otmoor and Farmoor a number of times. Despite the amount of surface water everywhere after such a wet spring the level of sightings in the county was not outstanding, but a very respectable cross section of regular waders was nonetheless recorded.

Avocets at Dorchester, courtesy of Tom Stevenson

Knot, courtesy of Nic Hallam

Black-tailed Godwit in summer plumage are always a joy to behold though, especially when looking this good (below). These were noted in several locations as in most springs, with 20 plus on Otmoor at month's end in company with two Bar-tailed Godwit. Jack Snipe continue to be reported in new places, the latest being near Rushey Lock on 5th.

Bar-tailed Godwits Otmoor rspb courtesy of Peter Alfrey

Black-tailed Godwit, courtesy of Nic Hallam

There was a strong movement of Little Gull through Farmoor up to 16th, with an impressive 20 passing by on 15th after a squall.  Elsewhere this diminutive larid was recorded at Otmoor (3rd) and Sonning Eye (10th). A first summer Mediterranean Gull was seen at Farmoor on 8th with the imm Iceland Gull still present until the 2nd. More Sandwich Tern moved through there between 4th and 19th. For other Terns the earliest records were Common Tern on 2nd at Farmoor, Arctic Tern at Sonning Eye (8th) and Black Tern at Farmoor (20th).

Amongst the winter lingerers, a Lesser Spotted Woodpecker at Wroxton (14&15th) was one of the more unusual finds. The Great Grey Shrike continued to winter at Baulking Pit early in to the month.

Lesser Spotted Woodpecker, courtesy of Colin Wilkinson

Some of the wet weather stragglers from March also continued to feature into early April until conditions improved, albeit briefly. A Whooper Swan remained at Otmoor up to 8th and Common Scoter were logged from three different sites through to 10th.

Lastly some winter finches hung on a little longer, the latest records being Hawfinch (8th), Brambling (13th) and Lesser Redpoll (20th). Is it really now goodbye again for the first of those after autumn 2017's irruption of continental birds into these islands? I'm sure I can speak for all Oxon birders in saying we will be sorry to see them move on.

So all in all it was an April of just a few headline but plenty of good county birds, and an excellent species total from the many contributors to this blog. Another month remains before the fascinating and ever constant rhythm of bird migration, with all its fluctuations and nuances, abates temporarily after another spring season. May should no doubt hold plenty in store for the next reviewer.


Peter Law

The Hinksey 'Chiffchaff'  April 2018.

Hinksey Chiffchaff (R.G.W)

The discovery of the Hinksey Chiffchaff in mid April 2018 generated much interest from both near and far and the fact that it was found independently by two different birders on the same day at such an innocuous location was remarkable. Its very unusual song lead to both observers concluding that it was probably an Iberian Chiffchaff, a rare visitor to the Uk with only one previous record in Oxon in April 2000 at Great Tew. The Hinksey bird appeared to be holding territory, rarely straying far from its favoured bushes. This enabled many local and not so local birders to study it at length both audibly and visually, as it conveniently sang constantly and wasn’t shy.

Iberian Chiffchaff is a relatively recent split and following the publication of Collinson and Melling’s id paper in BB in April 2008 records have increased as the identification criteria has become better understood. Separation from Common Chiffchaff depends principally on vocalizations together with subtle morphological and biometric differences.

Being such a rare species with a challenging identification many a critical ear and eye were cast over the Hinksey bird during the first few days of its stay and it wasn’t long before doubts were muted about its true indentity. Mick Cunningham was the first to suggest that it was missing a crucial mid section of its song. As can be seen on the sonograms below Iberian Chiffchaff has a ditty made up of three phases lasting about 2.5 seconds in total roughly translated as ‘jip jip jip jip jip weep weep weep chitachitachita’.

The Hinksey bird, however, had a two phase song ‘jit jit jit jit jit juda juda juda juda’ without the diagnostic ‘weep weep’ mid section. It also had brief periods of singing a Common Chiffchaff-like song.

And then there was the call. It didn’t utter this very frequently (too busy singing) but eventually it was heard clearly and recorded (see sonogram below) and matched Common Chiffchaff.

Common Chiffchaff

Hinksey Chiffchaff

Visually, as with any warbler (or bird!) its colour morphed radically. In some lights it was dull and monochrome, at other times it was bright and colourful and digital photographs enhanced or subdued these appearances depending on the camera settings and post production Photoshop tinkering. It could appear quite Iberian-like with a lemon wash to the breast and undertail coverts, a Willow Warbler-like face with a good supercilium and extensively orange lower mandible, a paler greenish rump and plumbeous legs. At other times it was unremarkable. 

Looking quite Willow Warbleresq (I.L)

Showing orange lower mandible (I.L)

Biometrically it appeared to be a bit ambiguous. The quality of photographs today means that details of wing formula can now be seen in the field without the need to catch the bird. Accurate interpretation of the photos is key, making sure the area being judged is square-on. As can be seen by the accompanying images the relative outer primary lengths on the open wing seem to match collybita, however, the primary spacing on the closed projection (suggested as indicactive of Iberian by Gil-Velasco 2017) better fit Iberian. The latter feature, however, appears to be rather variable in collybita.

I.L

In Iberian p2 is long, about the same length as p6 and about 6mm shorter than the longest two p3 & p4 with p5 about 3mm shorter. In Common p2 is shorter, about the same length at p7 about 8mm shorter than p3. p5 is a similar length to p3 & p4.

On the photo above it could be interpreted that p2,3 & 4 are curved away slightly and are actually longer than they appear.

R.G.W

Primary spacings match Iberian. The space between p6 & p7 is meant to be much greater than the space between p7 & p8 in Common Chiffchaff  with those two gaps roughly equal in size in Iberian


Interesting observations of the Hinksey bird included:                                

1) Not habitually pumping its tail as Common Chiffchaff.                                                                                2) Regularly uttering its song in mid-flight, something Common Chiffchaff is not known to do.              3) Having consistently sang ‘its’ song for two hours, Iberian Chiffchaff song was played back to the bird and it immediately reacted by commencing a Common Chiffchaff type song. Apparently this represents the typical ‘conflict’ song of Iberian Chiffchaff in response to a rival.                                        4) It did not have a moult contrast in its outer primaries (only shown by 1st summer Iberian: Demonglin 2013; Castello Massip & Gil-Velasco 2013) quashing any suggestion that it may be a young Iberian that had yet to learn its song.

So unfortunately the Hinksey Chiffchaff didn’t tick all the boxes for Iberian, however, its consistently odd song, different behaviour and the subtle presence of a few supportive morphological features makes it too simplistic to merely call it a Common Chiffchaff. Perhaps it was a hybrid, who knows, but the Hinksey Chiffchaff certainly instigated much interest  and debate about this complex taxon.

Many thanks to all those who provided in depth discussion and comment. Particular appreciation goes to Mick Cunningham and  to Dave Pennington for producing the sonograms. And, of course, well done to Justin Taylor and Julian Howe for alerting everyone to the birds presence in the first place.

Ian Lewington.



O.O.S Open Day this Saturday 5th May