More on moult

Continuing the theme of arrested/suspended moult I searched through some of our Demon records today. Between 1/1/18 and 1/1/23 we have processed 28,754 birds; of these, 17 are recorded as having arrested their moult (as arrested is the only option in Demon, I will just use this term from now on).

Of these 10 were female:
1 – Lesser Redpoll
1 – Whitethroat
2 – Greenfinch
6 – Goldfinch

5 were male:
1 – Garden Warbler
1 – Greenfinch
3 – Goldfinch

and 2 were unsexed:
1 – Whitethroat
1 – Goldfinch (though provisionally sexed as a female).

These totals don't include Holly's whitethroat, or my Linnet (see below), as these were recorded as in main moult but looking likely to have arrested their moult, which makes me wonder how many others were like this. (Also, its unlikely we would have recorded arrested moult in the secondary feathers).

Two things which jump out from our totals are -
1 - the number of Goldfinch. Could it be that perhaps we have caught more of these or perhaps a moult limit is easier to see, I don't know.
2 - the number of males. The article – Moult interruption in passerines resident in Britain by D G C Harper, found that this had only been recorded in females, though more information was needed.

And a final word from D G C Harper in their 1984 article -

“The increasing number of non-migratory birds in which moult interruption associated with breeding has been recorded suggests that ringers should pay careful attention to birds caught during the moult period that are not in active moult. Although the paucity of previous records of moult interruption in such species is probably a reflection of the low frequency with which it occurs, it may also reflect a tendency for observers to assume that birds whose feathers are all fully grown have either not started or have completed their moult”.

Mick P

Ramsdale Park Golf Centre - Saturday 29 July

Avoiding a Triathlon event at Skylarks, we met at Calverton Golf Club this morning on a bright
and breezy day. Not ideal conditions for our rides at the Golf Club, which are pretty exposed.
But we still managed a solid catch of 40 birds, mostly young warblers with 4 adult retraps.

Following on from Mick P’s post below, we also had a Whitethroat that appeared to be
arresting/suspending its moult, though it did have one primary still in pin (see photo).

We talked about the possibilities of using traps in the garden while it’s too windy to use mist
nets, and Josh shared a delicious homemade chocolate cake.

Holly

 

Arrested or Suspended - who knows?!

 

 

This female linnet caught this morning prompted me to look at the confusing issue of arrested or suspended moult.

Although still in main moult with a primary moult score, on both wings, of 5400000000, it looks possible that it wont drop any more primary feathers, so it may have arrested or suspended its main moult. But which is it?

Moult and Ageing of European Passerines by Lukas Jenni and Raffael Winkler says –

'Following Harper (1984), the phenomenon by which a moult stops before the whole plumage has been renewed is called moult interruption. This term and the related terms suspended and arrested moult have generally been used only for primary and secondary moult and, in order to prevent confusion, we retain this usage. Two different types of primary and secondary moult interruption are recognized (King 1972, Harper 1984). In the case of suspended moult, the primary and/or secondary moult is subsequently resumed at the point of interruption. Thus, the suspension normally divides a single moult into two temporally separated phases. Those primaries and secondaries not moulted during the first phase of the moult are renewed later during the second phase. In the case of arrested moult, the next primary and secondary moult starts at the normal site of initiation or another site other than the point of interruption. Thus, an arrested moult cannot later proceed to completion and the subsequent moult is in fact a different moult entirely.'

So, unless this bird is retrapped before its next “recognised” moult cycle its impossible to say if it has arrested or suspended its moult. However the “BTO Moult code flowchart for birds age 4, 5, or 6” (and DemOn) only gives the option to record arrested moult (perhaps here used synonymously with Jenni & Winkler's moult interruption), so if it had finished its main moult it would have to have been reported as arrested moult.

A further search of the internet found one of the articles referred to above by Jenni & Winkler - Moult interruption in passerines resident in Britain by D.G.C. Harper. This contains the following statement –

'Moult interruption during breeding has also been reported in unpublished studies on Whitethroat Sylvia communis, Willow Warbler Phylloscopus trochilus, Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella (R.A. Cawthorne cited in Ginn & Melville 1983; M. Lawn cited in Boddy 1983; and M. Boddy cited in Boddy 1983). Unfortunately no details have yet been published. It is however interesting that only females are mentioned in these reports; this raises the possibility that moult interruption in these species is more prevalent among females than among males. All these instances are reported as involving moult suspension; evidence supporting this interpretation would be valuable.”

I've also seen this in a female Whitethroat (see our Blog for August 2020). Interestingly, I also retrapped this female in September 2021 and it appeared to have Arrested its moult again.

Mick P

Skylarks NR - Tuesday 18 July

A break in the weather - Tuesday was the only dry and still morning for weeks, so we put the nets up at Skylarks and hoped for the best. With the help of sound lures we managed to catch 104 birds - by far our best catch of the year. Over 90% of the birds processed were juveniles, mostly Blackcaps and Reed Warblers. Highlights included Reed Bunting, Sedge Warbler, Treecreeper, and Mick P’s first Cetti’s Warbler.

With this being the first big catch of juveniles, it seems likely that nesting was late this year owing to the the weather. Fingers crossed for more evidence of breeding success.

Holly

 Song Thrushes, Treecreeper and Reed Warbler, Skylarks NR, 18 July 2023 (H. James)

Skylarks NR - Sunday 9 July

A very humid start to the day at Skylarks produced fewer birds than last week, with 48 in total. This included a large number of juvenile Reed Warblers, as well as a Whitethroat and 4 Greenfinch. A few Sedge Warblers are present at the site and have now been recaptured a number of times.

Alex

Reed Warbler and Robin (J. Holness) and Sedge Warbler (A. Turnbull)

Skylarks NR – Sunday 2 July

Despite the breeze on Sunday, we recorded our best ringing session so far this year. At Skylarks, we caught a total of 60 birds, many of which were juveniles. Highlights included a Greenfinch, a flock of 4 juvenile Great Tits, a Whitethroat and a Lesser Whitethroat (pictured). 

Joshua