Thursday, 18 August 2016

Oxwich Marsh 18 August: a Gower Rarity

An odd morning in some ways. Warm, still and close, with early fog rapidly lifting.Very few birds were present in the marsh (26 in four hours suggested a clear out the night before / a lack of influx), but what there was there was well worth the trip out.

Due to limited personnel we only put a small amount of net up. The pipit triangle and seven forty foot nets through the reed bed. The first bird of the day was a garden warbler, and an hour later we caught a second. These were numbers 8 and 9 of the year, a good total for a fairly irregularly recorded autumn passage migrant in Gower.

Willow tit (Keith Vaughton)
Having put the pipit nets up, and had a look at the South Pond, we were just walking back to the ringing field when we heard a vaguely familiar call. It took a few seconds to register that it was a willow tit (a less than annual species in Gower in recent years). We started to look for it. The bird was flitting around in some scrub. It called again, pausing in open view long enough to reveal a pale wing panel and fairly buff-looking flanks / underparts. 

Willow tit wing with fairly understated pale panel
As we were only about 50 m from the pipit nets, I made my way back and put on a willow tit tape. The bird instantly became alert and flitted through the scrub, moving towards the tape. We left for a few minutes, returning to find it in one of nets. Given the calls, views and attraction to the tape, separation from (the very similar) marsh tit was not really in doubt, but catching it potentially allowed conclusions to be drawn with regard to age and/or sex.

Back at the ringing table we made a close inspection of the bird, and measurements were taken. The wing and tail feathers were very fresh, there was no evidence of a re-feathering brood patch, but some tracts of body feathers were being moulted. Given that an adult willow tit would likely be in main moult in mid-August (typically main moult takes place between late July and early September), but that the flight feathers were very fresh and there was extensive pin on the body, it was determined as a a young bird in post-juvenile moult (age/moult code 3JP). A relatively understated wing panel is typical of young willow tits; adults have paler fringed inner secondaries and terials which makes the feature more obvious. The panel is visible in the photos.

The wing of the British subspecies of willow tit, kleinschmidti, typically measures 55-63 mm (marsh tit 59-71) (Svensson, 1992; Demongin, 2016). Ours, with a wing length of 59 mm was near the middle of the willow tit range but right at the bottom of that of marsh tit. Another feature that is considered useful in separating freshly-plumaged willow tit and marsh tit is that the 6th tail feather falls more than 4 mm short of the tip of the tail in willow tit (marsh tit tail feathers are usually less than 5 mm short of the tip). Our bird had a difference of 5 mm. Although marsh tit cannot be ruled out on these features, they are the shortest wing length and the longest tail difference recorded in marsh tit respectively, but typical of willow tit. 

Willow tit tail showing pale edges and indicating the length
difference between the central and outer feathers.
Demongin lists further features that are typical of willow tit. Some of these are rather subjective: the bill is more elongated than that of marsh tit; willow tit tends to lack a pale cutting edge (and if present this in on the lower mandible; the lack of a well-defined black bib, and whitish cheeks and sides of the neck are typical of willow tit (the latter are often grey-brown in marsh tit). The top photograph indicates that our bird showed all of these willow tit features.

Other interesting notes from Demongin concern iris colour, which gradually changes from dark brown in juveniles to light / rufous brown in adults, and pale edges to the tail feathers in juveniles. Our bird showed both a dark iris and pale edges to tail feathers, indicating a juvenile (see photos).

On release the bird flew approximately 50 m north-east to an area of scrub. It promptly started its nasal calling again.

The next net round produced two stonechats. The following round produced another, The only frustrations of the day were a kingfisher that bounced out of a net and a complete lack of migrant tree pipits in the nets despite a haul of sixteen a few days ago.

Many thanks to Heather Coats, Keith Vaughton and Ben Rees for company and assistance.

Owain Gabb
21 August 2016


Stonechat (Keith Vaughton)

Stonechat (Keith Vaughton)

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