Variation in first summer Great Skuas

Off Flamborough and the Azores

Moult matters!

It’s almost October. The best month… potentially… to get a South Polar Skua.

Learning to read moult scores may well secure Britain’s or NW Europe’s next SPS. From now on (peaking October?)  the loop migration of South Polar will take individuals closer to Europe than at other times.

With a summering Great Skua at Flamborough (previously featured) and photos of 2 birds off the Azores last April, I found it a useful exercise to be a bit more genned up. Dick Newell who has spear-headed much though on large Skua ID and moult kindly chipped in.

In June – July 2015 one notable Great Skua summered off Flamborough. The bird occasionally came close enough to capture some images. I posted HERE to open discussion. In the final analysis I change my gut reaction view and now I think the bird is in fact a first summer (2cy) individual (‘cos I am slow and some folk helped me!)

Reading Moult Score. Only new feathers score points

Let’s keep it simple for now.

The birds (skuas in this case) have OLD primaries, NEW primaries and primaries in various stages of REGROWTH, once the old feather has actually fallen out. Each of these stages can be scored.

P.S. you know I am only doing for myself, as I can never remember and need quick reference spot 🙂

OLD: If the feather is still present and OLD – NO POINTS- NOTHING!

NEW: If the feather is fully grown and NEW – full 5 POINTS

REGROWING: and here’s the slightly more tricky bit…

If the feather is NEW and regrowing but incomplete:

new feather NOT visible (in pin) 1 POINT

new feather visible and c 1/3 grown 2 POINTS

new feathers visible and c 2/3 grown 3 POINTS etc

That’s very roughly it! So only NEW feathers get POINTS whether fully grown or part grown or the gap where there are growing (in pin). Easy!

Flamborough, late June

A first summer Great Skua- moult score 32. Three old outer primaries (no points). Five new fully grown inner primaries. 5 x 5 = 25 points. then Dick has found 7 more points. Hmm need to check where he’s got them from…  Have I got that right?

Great Skua 28th June M Garner d (1 of 1)Great Skua 28th June M Garner a (1 of 1)Great Skua 28th June M Garner e (1 of 1)Great Skua 28th June M Garner g (1 of 1)





Dick Newell:

“Moult score of about 32 on 28th June puts it in the zone of 1st cycle Bonxie or very early moulting older South Polar – which is not a contender for SPS on plumage.”

Flamborough- same bird – now mid July

Bonxie boy (1 of 1)

Flamborough – different bird? – 15th August

Thanks to Craig Thomas for these pics. Watched this one fly close and it was not too tricky to age as a first summer Bonxie (Great Skua). This bird is just completing its primary moult. This is a ‘classic’  first summer/2cy in which the streaking etc is more limited to the mantle and scapulars/central body strip in flight but the upperwing is relativly plain and unstreaked (adults heavily streaked). Lots more in first Challenge Series: AUTUMN.

15-08-17 Bonxie image 2 15-08-17 15-08-17 Bonxie Flamboro


Azores – April

Peter Howlett sent these photos to the Birding Frontiers team for comment. Not an easy subject and with different climatic conditions, some birds in this region, even though they are also first summer Great Skuas, can be far paler, more bleached and frankly carry of a nice South Polar Skua search image in their appearance.

They often provide a South polar pitfall!

“I’d like to have your (and the team’s) opinion on these skuas I photographed just south of Sao Miguel, Azores on 13 April this year.

Reply from Dick Newell:

Hi Martin (and Peter),

How nice to hear from you and thank you for sending this.
The bird with a primary moult score of ~25 on April 13th is overwhelmngly likely to be a 1st cycle Bonxie. It would be a rare event for a South Polar to have this score on this date. Apart from which, it looks like a Bonxie and doesn’t have the compact profile of a South Polar – but that’s subjective stuff.

The second bird looks pretty similar to the first bird, so, on those grounds it is probably also a Bonxie. The primary moult score of ~2-4 makes it marginal. An older than first cycle South Polar could have this moult score (just), but more likely a late-ish 1st cycle Bonxie.

It would be unusual for a South Polar to look as mottled as these birds. The dark hood is also a point against, though can happen on a South Polar.



Sao Miguel

Sao Miguel

Sao Miguel

Sao Miguel



Sao Miguel

Sao Miguel

There’s a wee warm-up on skuas, ageing and moult scores. While passerines may dominate my desk for the next couple of weeks… we are also entering a South Polar window.


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