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Tern at East Chevington (1 Viewer)

Deb Burhinus

Used to be well known! 😎
Europe
Looks like a 1st summer Common Tern. Too dark for Roseate, and too long-legged for Arctic.

Brett

First Summer (or 1st s Arctics) would be fairly unusual in UK (they tend to stay on their winter grounds for the first summer) also, the outer primaries don’t look dark to me so I would be interested how you (and others) are so confident in aging this bird? Terns are notoriously difficult to age accurately in non-breeding plumage as anything other than immature or adult, even in the field.

https://britishbirds.co.uk/wp-content/uploads/article_files/V94/V94_N06/V94_N06_P268_277_A002.pdf

https://www.birdforum.net/showthread.php?t=200949
 
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Brett Richards

Well-known member
United Kingdom
First Summer (or 1st s Arctics) would be fairly unusual in UK (they tend to stay on their winter grounds for the first summer) also, the outer primaries don’t look dark to me so I would be interested how you (and others) are so confident in aging this bird? Terns are notoriously difficult to age accurately in non-breeding plumage as anything other than immature or adult, even in the field.

https://britishbirds.co.uk/wp-content/uploads/article_files/V94/V94_N06/V94_N06_P268_277_A002.pdf

1st & 2nd summer Arctics are not unusual in the UK. Go to any Arctic Tern colony and you will see a few. Ok, ageing can be a bit dodgy, but 2nd summer s are usually more advanced than this bird - fainter carpal bar and reddish legs & bill. In any case this is not an Arctic as it is too long-legged, but the same things apply to Commons.

Brett
 

Deb Burhinus

Used to be well known! 😎
Europe
1st & 2nd summer Arctics are not unusual in the UK. Go to any Arctic Tern colony and you will see a few. Ok, ageing can be a bit dodgy, but 2nd summer s are usually more advanced than this bird - fainter carpal bar and reddish legs & bill. In any case this is not an Arctic as it is too long-legged, but the same things apply to Commons.

Brett

Do you have literature or ringing data on specifically 1st Summer Arctics or 1st Summer Common Terns in the UK during the breeding season? I would be interested to see the data for prevalence of either. (I did not include 2nd summers in this question as you did btw nor any sightings outside of breeding season)

As for aging, I understand the moult strategy of Commic Terns is complex and there has been revised literature contrary to the standard guide books. There is a lot of overlap/variations among individuals which is why I pointed to the article in BB - is it very possible (in the absence of ringing data to the contrary) many of the ‘1st summer’ Commic Terns seen during the UK breeding season are actually 2nd summers?

Clear-cut, age- related plumages do not exist for Common Terns during the breeding season, and the overlap in appearance between different age categories is so large that only a very small minority of individuals can safely be aged (BB 94 pp268-277 June 2001)

https://britishbirds.co.uk/wp-content/uploads/article_files/V94/V94_N06/V94_N06_P268_277_A002.pdf


Personally, imo, in addition to overlap of moult features, the image is not of clear enough quality to assess the feather wear (but as stated some of the outer primaries do though look fresh and evenly light grey on my monitor (see here for moult strategy http://birdwatchidblog.blogspot.com/2011/08/common-and-arctic-terns-in-spring-and.html ) but now (ie during the breeding season) it can be difficult to distinguish 1st and 2nd summer Artic or Common) - some of the ‘darkness’ on the carpal area looks like underexposed/shadow and bare part colouring is also hard to assess accurately (the bill certainly is orangey/yellowing at the distal end).

I would be very interested in views (and data) on aging/moult contrary to those stated in the linked articles - thanks.
 
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Brett Richards

Well-known member
United Kingdom
Hi Deb

The article you referenced is June 2001, not 2011.

I can only see the bill as all-dark. In table 2 on page 272 of that article it says only 1.3% of second-summers had an all-dark bill, so the East Chevington bird would be a very unusual second summer, but it doesn’t appear to have ‘lobed’ ear-coverts, so perhaps that is what it is.

Brett
 

Deb Burhinus

Used to be well known! 😎
Europe
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KM1

Well-known member
This is not a Common Tern, it is, as Stuart suggested, a very typical first-summer type Arctic, which are much more numerous ( at least here in Wexford) than the equivalent plumaged Common Tern. Commons in this plumage-type, be they first-summers or older are generally in primary moult, have a slightly different extent of black on the head and a slightly longer and less ‘spikey’ bill. The visible leg-length depends on posture - it is not unusual for Arctics to look as long-legged as this...
 

Brett Richards

Well-known member
United Kingdom
Hi Killian

My first thought was Arctic, but then I considered the legs were too long, but I wouldn’t argue with you. Re. the primaries, I can’t see any difference between those of the East Chevington bird and those of the first summer Common (also in June)in plate 158 on page 273 of the article Deb referred to, but perhaps I’m missing something (I’m good at missing things recently); also the bird in plate 159 below on the same page has a short-looking bill. Agree about the head pattern though.

Cheers

Brett
 

Deb Burhinus

Used to be well known! 😎
Europe
Thanks for posting the write up Brian.

For more detailed (headier!) reading on molt/aging 2cy/3cy Arctic terns, this study on specimens indicates retrice molt could be helpful in separating first summer and second summer plumages

https://sora.unm.edu/sites/default/files/journals/jfo/v068n03/p0400-p0412.pdf

Paraphrasing slightly- The shape and coloration of the outermost retrices “proved to be a reliable indicator of age” for these age groups. During the first flight feather molt ie end of 1cy beginning of 2cy, birds loose their 6th (outermost) retrices (which are short) with either both vanes mostly white or with outer vane grey and the inner vane white, and replace them with grey feathers which they carry most of their 2cy - In ringed specimens, both vanes of the new feathers were dark grey and tipped with a white spot. They were also shaped differently than those found after later flight feather molts - after the first flight feather molt (2cy), the 6th retrices are wedge shaped but after subsequent flight feather molts, the 6th retrices are narrowly tapered. After the second flight feather molt, (end of 2cy beginning of 3cy), birds possess 6th retrices more adult like in both coloration and shape (showing little gray and tapered).

The length of the 6th retrix and the difference in lengths of the 5th and 6th ‘do not significantly differ‘ between 2cy and 3cy.
 
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KM1

Well-known member
No Brett, you're not missing anything! In this instance, I should have refrained from making reference to differences in moult strategies, as these are complex and highly variable in both species; 2nd cy+ Commons at this time of year often show signs of active moult in the outer primaries, but some look quite fresh and neat, similar to the bird in question, and to virtually all 2nd cy-type Arctics, in June. I see a lot of first-/second-summer type Arctic Terns here in Wexford, with usually a hundred or more being present at Our Lady's Island in July, where both species breed in good numbers. Immature Common Terns, however, are much less numerous, with probably no more than ten birds in a season. Despite considerable individual variation in the appearance of the Arctics, most are readily identified at a glance by their highly distinctive shape, structure and head-pattern. Leg-length is often useful, but beware of Arctics that look long-legged and Commons sometimes looking surprisingly short-legged.

I attach a montage of the bird in question and a similarly plumaged Common Tern to illustrate the characteristic differences in head markings that often assist identification. Also, an adult Arctic with long-looking legs and and adult Common with shortish-looking legs...
 

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Deb Burhinus

Used to be well known! 😎
Europe
Hi Killian

In your montage you age the OP Arctic Tern as a 2cy and not a 3cybecause of the ‘dark’ outer primaries (suggesting very worn outer primaries rather than ‘shadow/poor lighting in the image which I put it down to initially). I’m interested partuculary to know why you would use this in particular as a distinguishing age factor between 2cy and 3cy plumage type birds? I am hoping you can clarify this reasoning please.

I understood immature Arctic Terns (including hatch year/2cy birds) also have a complete molt of flight feathers (beginning with inner primaries and secondaries) over the beginning of the calander year as with adults. (So I would have expected spring/early June birds ( ie in cf to Common Terns) to exhibit little or no contrast between the outer and inner primaries). Even allowing for delayed molt in post-juvenal birds (due to less time constraint re breeding and much longer time required to molt, wouldn't delayed active molt evidence apply rather to the retrixes rather than remiges?). I’m thinking following your post, molt strategy couldbe a useful age criteria if 3cy birds have a different molt strategy to 2cy birds ie if the latter do not undergo a complete primary molt in their first flight feather molt at the beginning of the calendar year (but I can’t find anything in the literature to help clarify this)

Again, I am not disputing the ID of course, but, as with my earlier posts, seeking further clarification on the molt strategy/score when it comes to age identification as this helps me to understand the migratory movements of 2cy/3cy terns in the breeding season and the prevalence of the respective age groups at tern colonies.

Also, I would be interested your comments on the aging of the Arctic Tern in Brian’s link (it looks like a better candidate for a 3cy to me but I’m still struggling with aging these 2cy/3cy type birds down to a calendar year in these few spring migrants.). Also, have you found 6th retrix distinguishes helpful in the field (as per my previous post) - I’m wondering how useful it would be in the field (given these were in the hand specimens!)?

Thank you for your time and input.
 
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KM1

Well-known member
Hi Deb,
I was a little puzzled by your question at first, but when I looked again at the montage of the two terns I uploaded yesterday, it suddenly made sense; the annotation in the middle of the montage, referring to the dark and apparently worn outer primaries alludes to the Common Tern in the lower half of the montage, rather than Arctic at the top!
I'm afraid I don't have a clear-cut solution to the problem of telling 2cy Arctic Terns from 3cy at this time of the year, other than guessing that the ones with a very short tail , 'masked' appearance, clean white underbody and all-black bill are likely to be 2cy, while the longer-tailed birds, with more of a ''cap' and grey smudged underbody and red in the bill are perhaps more likely to be 3cy.

I have read the Gary Voelker paper you supplied a link to - or at least the more readable parts of it - but I have not made a significant effort to see how useful/practical the outer tail feather differences he describes may be in ageing birds in the field. What a pity the paper does not contain so much as a diagram or sketch to give a more precise idea of the difference between a 'wedge-shaped' tail feather and one that is 'narrowly tapered'. As far as I can see, there appears to be almost a continuum between what might be considered classic 2nd cal-year types and 3rd year-types, but perhaps more particular attention to the tail-feather details will allow a distinction to be made? A project for the coming weeks! Incidentally, I have noticed that quite a few 2 cy-type Arctic Terns (which invariably have a full, clean set of quite fresh looking primaries in June) start to moult the innermost primaries in late July, a moult that I have not found reference to anywhere? I will let you know if I make any progess with regard to establishing useful differences between 2cy and 3cy Arctic Terns.

Kind regards,

Killian
 

Deb Burhinus

Used to be well known! 😎
Europe
Hi Deb,
I was a little puzzled by your question at first, but when I looked again at the montage of the two terns I uploaded yesterday, it suddenly made sense; the annotation in the middle of the montage, referring to the dark and apparently worn outer primaries alludes to the Common Tern in the lower half of the montage, rather than Arctic at the top!

ha! that makes sense (I did wonder after posting whether that was the case)


...Incidentally, I have noticed that quite a few 2 cy-type Arctic Terns (which invariably have a full, clean set of quite fresh looking primaries in June) start to moult the innermost primaries in late July, a moult that I have not found reference to anywhere? I will let you know if I make any progess with regard to establishing useful differences between 2cy and 3cy Arctic Terns.

Thank you for clarifying your thoughts on ageing, it’s much appreciated. As far as the inner primary moult in the post-breeding period, prior to winter migration, as I was reading one of the studies I linked to earlier, I noted mentioned an additional primary moult of the inner primaries (only) which is generally not referenced. I’ll try and pull out the relevant reference and paste it in.

So it’s confusing (and I could be guilty of muddled thinking) - In Voelker’s paper (linked above) in discussion starting on page 409:

The SIPM (Second Inner Primary Moult) seems to apply to adults and overlaps with the main flight feather moult on wintering grounds - the moult timing for HY is such that based on specimens, did not commence before winter migration whereas for sub-adults (2cy/3cy) commencement of primary moult can predictively be initiated before winter migration to compensate for protracted migration periods/longer time (double?) to complete a moult cycle than adults. Where this leaves the status of whether the inner primary moult on subadults in July is an additional moult or not, I’m not clear perhaps someone else can interpret Voelker’s discussion more clearly than I can!
 
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KM1

Well-known member
Hi Deb,

I don't believe your thinking is muddled at all, but I have to admit, I am finding it very difficult to get through the Voelker paper that you linked above, and this is not my first attempt to do so! There are a number of very disconcerting aspects to this paper, the principle concern I have being that so many of his conclusions are based entirely on analysis of skins, most of which (apart from juveniles and 2c-y with retained juvenile feathers) would have been of unknown age (though it might be safe to assume that all breeding plumaged adults at least in their 4 cy). In the outline of the methodology applied, under the sub-heading of Age identification (p403) the author states:

"I sorted all specimens into the following age classes (from Pyle et al 1987): hatching year (HY), birds in their first calendar-year; second year (SY), birds in their second calendar-year; third year (TY), birds in their third calendar-year; and finally after third year (ATY), any birds in at least their fourth calendar-year."

It is important to understand that "from Pyle" here means that he copied Pyle's age classification, rather than that he assigned SY and TY birds to their respective age categories based on information in Pyle [Pyle does not actually provide much information on this problem]. So, how did Voelker sort his specimens? We can only guess that he did so on the basis of the outer tail feather differences he goes on to describe. Maybe he is right, but I am not convinced that this isn't an example of circular reasoning.

The next concern is that so much of his presentation is based on extrapolation of moult regimes, backwards and forwards, from his interpretation of what he is seeing in skins. In addition to the already mentioned serious shortcoming of the whole paper, that there is absolutely no illustration/photographic content by which readers might get a visual idea of what is being described (I can't help wondering, for example, if his references to 'scaled' feather patterns always refer to juvenile feathers, as is assumed, or could he actually be seeing something similar in finely patterned post-juvenile feathers?). Throughout the paper Voelker gives us detailed information on the moult score of particular specimens (for example at the bottom of p406) but he does not provide the all-important date, or even the month when the specimen was collected.

If, as is likely, the complexity and extent of individual variation in the plumage development in Arctic Tern is anything like it has been shown to be in Common Tern, there is really no way that a true understanding of what is going on will be gained from examination of museum specimens, where all but juveniles, or birds with retained juvenile feathers, will be of unknown age. I believe a correct picture will only emerge when we are able to examine and analyse in detail the appearance of individual marked (ringed) birds of known age, as was the basis for the excellent White & Kehoe paper on Common Tern ageing that you provided a link to earlier in this discussion.

I am glad to be reminded of this interesting ageing question, and will avail of any opportunities I get in the coming weeks to take another look at any sub-adult Arctic or Common Terns I encounter, especially the Arctics that, curiously, have started to moult their inner primaries.

regards, Killian
 

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Deb Burhinus

Used to be well known! 😎
Europe
Hi Killian

I agree that for a scientific paper, Voelker’s analysis seems rather chaotically structured and based on unclear parameters. I do note that he does assign age classes based on collection dates of specimens viv a vis the ‘known’ moult periods for Arctic Terns (but as you say does not present them in the moult score charts!) and does not attempt to sort 2cy/3cy into definitive calendar age but lumps them together for the purpose of the tail feather study. I’m not quite sure therefore, apart from circular reasoning as you suggest, how one arrives at the proposition that it is 2cy birds that have dark grey, wedge-shaped 6th retrix and not 3cy birds or vice versa when other plumage aging criteria for these 2 age groups has so much overlap. I also noted that specimens were obtained from very wide geographical range of breeding grounds so no account was made it seems, for any potential locally specific impacts on moult scores (due to winter migration distances and timing of moult) so it could be feasible some specimens had delayed or advanced moult due to locality rather than calendar year age.

Thank goodness for ringing studies!

Anyway, once again, thank you for your time and input and perhaps we can look forward to some enlightening field observations on aging criteria in the future ;)
 

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