Billinge 28th to 31st July 2017: More adult Willow Warblers

The weather hasn't been particularly favourable but I managed to get out on the last 4 days of July. I went up to Billinge and set 3 nets in on each occasion although I had to change the net positions on some days to get adequate shelter from the breeze. The 29th provided the best conditions but the sessions on the other days were restricted by light showers and or a strengthening breeze.

I made the effort because I was curious to see how many juvenile and adult Willow Warblers I would catch and if the proportion of juveniles would increase. A total of 100 birds (92 new & 8 retraps) were caught over the four sessions and almost half  (43 new & 4 retraps) were Willow Warblers. Interestingly, the proportion of adult Willow Warblers remained relatively high with 11 out of the 47 being adults, although one had been encountered earlier in the month.

Adult Willow Warbler showing quite an extensive pure white belly.

 The total number of individual Willow Warblers handled in July ended up at 104 and of these 77 were juveniles and 27 were adults which gives a simple ratio 2.85:1. While this is the lowest ratio of juveniles to adults encountered in any July the total number of juveniles handled this July is similar to 2014 & 2015 as can be seen from the table below. 2016 seems to have been an exceptional year for juveniles as a similar pattern was found when I looked at the July totals for Chiffchaff  (2014/42, 2015/45, 2016/73, 2017/40) and Blackcap (2014/35, 2015/42, 2016/65, 2017/41). So the number of juvenile Willow Warblers encountered this July has ended up in what might be considered the 'normal' range for the site.

July Willow Warblers
Year	Juveniles	Adults	Ratio (rounded off)	Visits
2017	77	27	3:1	13
2016	101	6	16:1	13
2015	71	14	5:1	11
2014	81	9	9:1	13

A ratio of just under 3:1 is much closer to the actual productivity of Willow Warblers but that is not what I am used to seeing at this site, hence my interest being sparked by the high number of adults encountered this year. There did seem to be more adults around in the spring so better over-winter survival resulting in a higher breeding population may have played a part, although it appears to be too much of a increase to account for it all. If a much higher breeding population was part or all of the cause then it still suggests productivity is low this year as more pairs would be expected to produce more offspring unless productivity has been negatively affected in some way. There is also the possibility that some of the adults were migrants rather than local birds as some were nearing the end of their moult and many adults will start migrating just before the innermost secondaries are fully grown. Either way I have caught a lot more adults this July than usual and multiple factors may be involved. As I said in my previous post it will be interesting to see how the 2017 CES results and other surveys compare.

 

Adult Willow Warbler showing more extensive yellow across the belly and a relatively pointed tail. This bird didn't shout adult and is the sort of bird that can trip you up if you're not careful and rely too heavily on a particular feature such as the colour of the underparts. Careful examination revealed it was still in active wing moult, but only just, as can be seen in the image below. 

Primary moult was just about complete but the big give away was the inner 2 secondaries that stand out as being that bit shorter than the longest tertial. Examination from underneath showed the inner 3 had some feather sheath at their bases. It is always worth giving those inner secondaries a look as the moult usually finishes with the innermost secondary rather than the outer primaries. 

I don't operate a standardised mist-netting regime so that has to be borne in mind when looking at the figures, ringing effort, however, was reasonably consistent so I still thought the figures were worth sharing. Willow Warblers are declining across the UK with the exception of Scotland and I am lucky to have a site that still has quite a good breeding population and also attracts good numbers of passage migrants (especially for an inland site). In 2016 a total of 367 Willow Warblers were ringed at the site which, like the 2016 July totals, was significantly up on the previous 2 years (2015/256 & 2014/240) so it will be interesting to see what the total looks like at the end of this year.

Highlights amongst the other birds caught included the first Garden Warbler of the autumn. A Whitethroat was also a first for the autumn but an unusually late one at that, I don't catch many Whitethroats at the site but I've usually caught a few juveniles well before the end of the month. Goldcrest on the other hand appear to be having a good year with another 10 bringing the total for July to 19. This compares favourably with the July totals for previous years - 10 in 2016, 8 in 2015 and only 3 in 2014.

Combined ringing totals (retraps in brackets) for 28th to 31st July 2017 were: Goldcrest 10; Blue Tit 3; Great Tit 4; Chiffchaff 4(2); Willow Warbler 43(4); Blackcap 7(1); Garden Warbler 1, Whitethroat 1; Treecreeper 1; Wren 4; Song Thrush 1; Robin 2, Chaffinch 1; Bullfinch 2; Linnet 5; Goldfinch 2 (2); Reed Bunting.

Garden Warbler. A scarce passage migrant at the site with most records coming in late July and early August.

Whitethroat.  A few pairs breed at the site so I usually catch a few juveniles in July but not this year.

Billinge: 22nd 2017 July

I had high high hopes for this session in the top willows by my optimism and early start wasn't rewarded. Equivalent sessions in previous years have produced good numbers of phylloscs and out of habitat migrants such as Sedge and Reed Warblers but that wasn't repeated today. The weather probably played a part as overnight rain probably put the dampers on any migration and the site was still shrouded in hill fog/low cloud when I arrived, although it soon lifted.

It turned out to be one of those days that was noteworthy for the birds that were absent or only present in low numbers and chief amongst those was Chiffchaff with only 1 recorded all morning, and that one only turned shortly before I packed up. There were fewer Blackcaps around than usual and although Willow Warblers crept into double figures a total in the high teens would have been nearer the norm. Once again, tits were few and far between and there was certainly no sign of any mixed tit/warbler flock formation. I didn't even hear any Long-tailed Tits nearby or in the distance. The only species that seemed to be present in higher numbers than usual was Wren with 5 ringed. I think Wrens should be renamed fidget spinners as this aptly describes their behaviour in a mist-net.

The final total of 32 new birds and 4 retraps wasn't bad but was lower than expected for late July. Totals for 22/07/17 (retraps in brackets) were: Great Tit 2; Willow Tit (1); Blue Tit 2; Chiffchaff 1; Willow Warbler 11 (1); Blackcap 3 (1); Treecreeper 1; Wren 5;  Robin 1; Bullfinch 3 (1); Goldfinch 2; Reed Bunting 1.

Adult Willow Warbler (all the photos below are of the same bird).
Three of the Willow Warblers were adults and two of them had almost completed their full moult.

Once the moult is completed, in probably just a few days for this individual, they start migrating back to Africa. They often start to put on fat just prior to the completion of the moult so they are ready to go with little or no delay.

Once the moult is completed Willow Warblers can only be aged by the colour of the underparts and shape and wear of the tail feathers. Adults have a white belly whereas juveniles are usually completely yellow or yellowish underneath.

Adult tail. Generally broader and less pointed and also showing less wear than the juvenile tail. The tail feathers are usually glossier too as they are newer than those of most juveniles which often look a tad browner.

Ageing Goldfinches gets more interesting.

This is a post for aficionados of moult, ageing birds in the hand and Goldfinches in particular but hopefully it will be of interest to others too. First year Goldfinches normally only have a partial post-juvenile moult in the UK and this usually involves the replacement of the body feathers along with most of the upper wing-coverts and tertials, and may also include some of the tail feathers. However, first year birds from populations in southern parts of Europe frequently have a more extensive post-juvenile moult which involves more of the upper wing coverts and can include some or nearly all of the flight feathers. Whether any actually have a complete moult, like adults, is open to question but if some do it may only be a fairly small proportion. It is probably better to think of it as an unknown proportion as it is an aspect of moult that is difficult to study so may be more common than the literature suggests.

Much of the literature on this subject is quite dated now and many ringers in the UK will have had experience of first year birds that have undergone a more extensive post-juvenile moult than was the case say 20 or 30 years ago. When I started ringing it used to be relatively rare for Goldfinches and Greenfinches to replace all their greater coverts as part of the post-juvenile moult but things have changed and it is much more common these days. That tendency for a more extensive post-juvenile (pj) moult hasn't stopped there and some Greenfinches also started replacing a few primaries as part of their pj moult. The inclusion of some primaries in the pj moult of British Goldfinches followed and there have been recent reports of first year Goldfinches undergoing a complete moult like adults. In a couple of cases that I am aware of the birds were ringed when they were in juvenile plumage and were considered to have undergone or were just finishing a complete moult when they were retrapped later in the year. I don't know how thoroughly these birds were scrutinised when they were retrapped but one of the reports suggested the extent of the moult was noticed at the time of recapture rather than being assumed from an age discrepancy on checking the original ringing details.

So where am I going with this and why is it interesting. Well I caught a Goldfinch yesterday that had undergone a very extensive post juvenile moult and it only just fell short of a complete moult. It had undergone the most extensive pj moult I have ever seen in the species and is the sort of bird that could get overlooked unless all the feather tracts are carefully examined. It had replaced nearly everything and the few feathers it hadn't replaced were not very obvious and are easier to see in the photographs than they were in real life. I had to turn the bird so the feathers caught the light just right and also played with the exposure setting on the camera to be able to show the differences between the moulted and unmoulted feathers. So lets have a look at it ......

I have included this photo to show that the moult limit in the primaries was not that easy to see. The outermost primary in the image is just that bit browner but remember this image is larger than life size. Also, and more importantly, the bird was held at just the right angle to the light to try and make the difference stand out.

Close the wing a little bit and adjust how the feathers catch the light and the difference is a bit easier to see.

Zoom in even closer and you can see the outer feather is a little more worn in addition to being brown but as the wear is relatively slight and the feather is not that bleached it rules out the possibility of it being an adult that has arrested its moult.

Here I have to admit that I thought the bird had replaced all of its primary coverts on the right wing when I examined it and only noticed that it had just replaced the inner 6 on reviewing the photographs. The contrast between the new and the old feathers wasn't as obvious in real life as it appears in this heavily cropped photo. Because of this oversight I didn't check the primary coverts on the left wing.

Zoom in a little more and it doesn't make the difference that much easier to see. The 7th and 8th primary coverts were unmoulted and the 9th (if Goldfinches do have a 9th primary covert) is so small its very difficult to see never mind age.

So here we have the left wing. I had to show it this way up as I can't use the camera in my left hand. The two outer primaries in this image just look a a tiny bit browner and the shape formed by the primary tips isn't quite right.

Crop in closer and you can see the outer two primaries in the image are browner, unmoulted juvenile feathers.

Zoom in further and the difference in colour is still obvious but the old feathers are only a little more worn. So it has moulted asymmetrically but only by 1 feather.

I was a bit less certain about the age of the tail feathers although I do think all the tail feathers have been replaced. There only appeared to be one generation of tail feather as there was no detectable difference in the intensity of the black between any of the feathers. They were too fresh looking for juvenile feathers although the 3rd, 4th and 5th tail feathers were a little bit more worn and pointed than I would have liked but then we have to bear in mind that it is March, if only just, and the tail feathers of adults are starting to show signs of wear at this time of year. If these were unmoulted juvenile feathers I would expect them to be far more worn and pointed and a little less glossy too. It is fair to say that it is not the most convincing adult type tail but then it doesn't look like a totally convincing first year tail either. 

This image shows all the tail feathers and the outermost (6th) tail feather on both sides appears to be very slightly less glossy black but this is an artefact caused by the light acting on the angle of the tail feathers. I just couldn't keep the tail totally flat so some of the feathers are in a slightly different plane and that affects their appearance. The shape of the feathers is just within the range shown by adult type feathers and I do have photographs of a known age adult with a similarly shaped tail. It was the appearance of the tail that initially set the alarm bells off in my head and caused me to have a really good look at this bird.

In this image we get a much closer look at the tips of the tail feathers and that wear. The tips of the feathers on the left side of the tail are slightly less worn than those on the right but it is marginal and not that unusual. The wear is fairly even within each half of the tail and supports my view that there is only one generation of tail feathers. The black portion of feathers  5L, 6L, 4R, 5R and 6R appears to be less glossy black than the other feathers but again it is simply an artefact of the light and is also a camera focus and depth of field issue rather than it being anything age related.

The tertials were interesting in that there was some uneven wear of the white tips with the middle tertial being a bit more abraded than the other two. They are all the same glossy black so they have all been replaced but the white tip of the middle tertials are showing more signs of wear. The white tips of the tertials in this bird are a little more worn than you would expect to see on an adult, even though they have been replaced like those of an adult, but that is probably because a first year undergoing an extensive partial post-juvenile moult will have started moulting earlier than an adult undergoing a complete moult. The replaced feathers on this bird could be up to a month or more older than those of a fully moulted adult and therefore should show more signs of wear. This difference in age of the new tertials on this bird compared to those of an adult may also explain why the tail is as worn as it is.

Here is an image of the right wing which clearly shows all the feathers are new apart from the outer primary and primary coverts as detailed above.

And here is the whole bird and it is a nice male it is too, not that its sex has any bearing on the extent of the pj moult.

So why is any of this interesting and why does it matter? Well, if it becomes the norm for some first year Goldfinches to have a complete moult then those that do will be indistinguishable from adults and potentially make it unsafe to age any Goldfinch as an adult. The error rate at the present time is likely to be small but it is unknown quantity and may not be as small as we would like it to be. Opinions will vary as to the level the error rate needs to reach before ageing Goldfinches as adults is considered to be too unreliable but we have to prove to what extent it is happening first. Unfortunately finding this evidence is intrinsically difficult for reasons I won't bore you with now but the fact that these juveniles become indistinguishable from adults is no small hurdle in itself.

The best evidence will come from retraps and some of that evidence may already be out there in the form of age discrepancies between the time of ringing and recapture. An indication that some birds are having a complete moult will come from birds that have been ringed when they are in juvenile plumage and and are aged as an adult when recaptured later in the birds first year of life. If this type of discrepancy becomes more common it potential points to more first year birds having a complete moult as opposed to errors in data recording and ageing. So what may initially appear to be a cock up could actually be a useful piece of evidence.

Another reason the change in the extent of post juvenile moult matters is that it is probably linked to climate change. Research is showing that some summer visitors are arriving earlier and a range of species are breeding earlier. The factors that are influencing those changes are likely to be involved with the tendency for some species, such as Goldfinches, to have a more extensive pj moult. Monitoring pj moult in a systematic way across a range of species could prove to be worthwhile and could be another useful indicator for demonstrating the effect of climate change.

Crawford: 12/12/2016 and wing moult in first year Blackbirds

I don't know what is happening with thrushes and Redwings in particular but there seems to more nocturnal movement than is usual at this time of year, especially given the absence of any cold weather. Some large nocturnal movements of thrushes were noted at Spurn Bird Observatory towards the end of last week and some of those continued in daylight hours at Spurn but more so at Sunk Island. These unexpected movements attracted the tongue in cheek comment 'Mild weather movement?' in the list of sightings for 9th December on the Spurn Bird Observatory website.

I have heard Redwings overhead well before first light on numerous occasions recently and that happened again when I was loading the car to go ringing on the 12th. When I got to Crawford I heard the calls of a few more Redwings going over in the dark in the short time it took me to set up the line of two nets. Whatever the reasons are for these movements it seems to translate into more Redwings being in the area and good catches at dawn, although they are remarkably inconspicuous during rest of the day. The net result, no pun intended, was that I caught another 16 Redwings on the 12th which took the number ringed so far this month to 131. It also took the number ringed since early October past the 1100 mark and to 1110 to be precise. How long these nocturnal movements and dawn catches will continue is anybody's guess but now that I have mentioned them they will probably come to an abrupt end. I will find out soon enough as I hope to get out to Billinge and/or Crawford later this week.

This is the one thousand, one hundred and ninth (1109) Redwing ringed this autumn/winter. Yes I know it is an odd number but the light levels were too low when number 1100 came along.

Whenever there are a good number of thrushes around one or more Sparrowhawks are never too far away and that was also the case on the 12th. Their presence sometimes reduces the catch of Redwings, especially when they make frequent sorties, but that is quickly forgotten about when one ends up being caught in one of the nets. Sparrowhawks have a bit of a reputation for getting out of nets, especially the larger females, but I have been lucky enough to catch 10 since early October with 5 of them being females.

2nd year Female Sparrowhawk. It is bigger than it looks in this photo. 

Blackbird was the only other species handled with 8 new birds and 2 retraps being caught. One of the first year males was particularly interesting because it had replaced some of its secondary flight feathers in both wings, which first years don't normally do. There was some asymmetry to the moult but it certainly didn't appear to be due to any accidental loss of feathers.

Eccentric moult in 1CY Blackbird LK6922 caught at Crawford 12/12/2016

A bit like the stockamsel plumage Blackbirds that I wrote about in my last post this was the second first year male Blackbird to come my way that had undergone a partial moult of the flight feathers. The first was a Blackbird that I retrapped in the garden on 22nd November, it had been ringed as a juvenile on 7th August so wasn't from a particularly early brood but it definitely made it a bird of UK origin. The moult of this bird was far more extensive and involved some of the primaries, primary coverts and secondaries, and all of the greater coverts, tertials of both wings, although there was some asymmetry. The entire tail had also been replaced.

Left wing of 1CY Blackbird LK25176 retrapped in the garden 22/11/2016

Tail of 1CY Blackbird LK25176 retrapped in the garden 22/11/2016

In recent decades it has become more common for finches to undergo a limited moult of the flight feathers as part of their (partial) post-juvenile moult but this phenomena appears to be a far more recent occurrence in Blackbirds and these two examples are the first I am aware of for the UK. A search of the Internet revealed a short paper about a juvenile Blackbird that was found moulting its primaries and secondaries in Poland in 2004. That appears to be the first account of a juvenile Blackbird replacing its primaries and secondaries and moult aficionados can find that paper here or by searching for the reference below.

As for the cause of the change in the extent of the pj moult in some birds I would put climate change as the number one suspect but as many of the species involved are also frequent visitors to gardens the more extensive and much improved quality of food provided in gardens may also be playing a part. It is certainly an area that is ripe for research and hopefully it will become something that the BTO will take more of a lead on by encouraging ringers to record and report any examples they come across.

References:
Zieliñska M., Zieliñski P., Mokwa T. 2005. Juvenile Blackbird (Turdus merula) moulting primaries and secondaries. Ring 27, 1: 121-123.

Billinge: 14th August 2016

Just a quick post as I need to get some sleep ahead of another early start tomorrow. Another good session at Billinge produced 59 new birds and only 1 retrap in the form of a recently ringed Blue Tit.

Willow Warblers continue to move through the site in good numbers and topped the totals yet again with 28 ringed. The proportion of adult Willow Warblers has increased now that most have finished their moult and are migrating with 6 being caught today. Adult Willow Warblers do not hang around once they have moulted and may even start to fatten up in preparation for migration before the end of their moult.

Freshly moulted adult Willow Warblers

Adult Willow Warblers usually have a much whiter belly and stand out from the more lemon yellow juveniles.

The majority of Chiffchaffs are still in their scruffy juvenile plumage or in the early stages of their protracted post juvenile moult so it was a bit of a surprise to catch one that had completed its moult. It is not particularly early for it to have done so but it was well in advance of all the others that have been caught recently. The only Blackcap caught had also completed its post juvenile moult and both were a reminder of just how quickly the season is advancing.

1cy Chiffchaff looking much sleeker now that it has completed its pj moult.

I was hoping today would see the first good passage of Tree Pipits but again it wasn't to be and only 4 were ringed from a maximum of 4 or 5 recorded. It was very overcast this morning (even the odd spot of rain at one point) and there was very little in the way of wind so that may have suppressed movement. It is not often I wish for brighter conditions and a bit more of a breeze when I am ringing but that is what it might take to get more Tree Pipits on the move.

One of today's Tree Pipits.

An interesting Reed Bunting was caught in that it was one of those birds that can easily catch out the unwary and it would almost certainly be wrongly sexed if just being viewed at a distance with binoculars. Even in the hand it looked like a male at first glance having a largely black head and blackish bib and it even had a noticeably white collar. However, careful examination revealed it to be a well worn adult female with a brood patch. The state of the brood patch suggested she was in the later stages of a breeding cycle and had probably just fledged a late brood. That was supported by the calls of recently fledged Reed Buntings that were heard near to where she was caught. Having said all that I am sure there will be some people that will find it hard to believe that it is a female and not a male given its appearance.

Adult female Reed Bunting looking rather male like. The cloacal shape and brood patch confirmed it was a female. It also had a very short wing length.

Ringing totals for 14/08/2016 were: Goldcrest 3; Blue Tit 4 (1); Great Tit 3; Coal Tit 1; Swallow 1; Chiffchaff 4; Willow Warbler 28; Blackcap 1; Whitethroat 1; Wren 1; Robin; Tree Pipit 4; Chaffinch 3; Bullfinch 1; Goldfinch 1; Reed Bunting 2. Total 59 new birds and 1 retraps.

Willow Warbler recovery

I recently received the recovery report for the control Willow Warbler that I caught on Billinge Hill on 7th August and it had been ringed at Leighton Moss 29 days earlier. Not a particularly long or fast movement but interesting nevertheless. Willow Warblers migrate through the Billinge site in good numbers and 157 have been ringed so far this autumn. There has been a fairly constant turnover of birds since mid-July and this recovery is the first to indicate the origin of some of those birds.



Willow Warbler migration across the country is peaking just about now and this first year bird may have already moved on and reached the south coast or be even be further south in France. Not bad for a bird that may only be about ten weeks old, yes little more than ten weeks old and on its way to sub-Saharan Africa.

While on the subject of Willow Warblers the following image shows the tail of a young bird that must have had a severe fault bar that caused the tip of the tail to break off. The two complete tail feathers are replacement feathers and show how much of the other feathers has snapped off. Fault bars are caused by periods of poor nutrition when the feathers are growing and are testament to the grotty summer we have had.

IY Willow Warbler tail. The juvenile tail feathers have sheared off along the line of a fault bar. The 2 complete feathers are newer replacements and are easily recognised by being darker and more glossy.

Adult Willow Warblers have or are just about to complete their moult now and can often be recognised by having whiter bellies than first year birds. It is not a totally infallible criteria, as a few intermediates do occur, but is true in most cases. The condition and shape of the tail feathers is usually the clincher where there is any doubt.

Willow Warblers: First year left and freshly moulted adult right.

Surprise 'Sibe'

I was joined by Wayne for a Redpoll ringing session at the baited site near Scotman's Flash this morning or at least that was plan. We erected 2 nets near the feeders and another net further away with an MP3 lure playing redpoll song. The idea of the set-up being that we would either catch birds coming to the feeders and or attract any others passing over to the lure and with a bit of luck both. The feeders had clearly been well used since I had last topped them up so we were optimistic about our chances of catching a few birds although the current fine spell of weather could have caused them to disperse or move on.

We heard the first Redpolls before we had finished erecting the nets but it was only a couple of small groups. There didn't seem to be that many birds about and the initial 2 rounds of the nets only produced 5 new Lesser Redpolls. Similarly, there seemed to be very little in the way of newly arrived migrants and literally nothing on passage overhead; no pipts, finches or wagtails of any description. A few Sand Martins were seen along with the odd Swallow but they didn't appear to be going in any particular direction in a hurry so may have been local breeders.

Quite a few Lesser Redpolls were attracted into the net by the MP3 lure and may just have been intercepted on their way to the feeders but interestingly we only caught unringed birds in this net whereas birds caught in the nets by the feeders were close to a 50:50 split of retraps and new birds. It may be that there were a few Redpolls on passage with some being attracted to the lure but if there were they must have been passing over a considerable height.

On approaching the net with the lure at about 07:30 we could see we had caught a couple of birds. One was obviously a Lesser Redpoll but the other was totally unexpected and a complete surprise.

What have we here then.

OK I have strung this out for long enough, it was a Siberian Chiffchaff as you may have guessed from the post title and a proper one at that. Proper in that it that it was the classic grey-brown and white of a 'tristis' without a hint of yellow and what little olive green there was being confined to the fringes of the primaries and tail feathers. Also it was just finishing its moult as some of the body feathers were still growing and partially 'in pin'. This late moult is also characteristic of Siberian Chiffchaffs from what I have read.

Siberian Chiffchaff (Phylloscopus collybita tristis)

Separating Chiffchaff races is not easy and there is a degree of overlap between tristis and abietinus in particular. A quick search on the Internet will find loads of articles on the subject some of which are much more helpful than others but beware some of the photographs and descriptions may leave you even more confused. Anyway in the absence of DNA confirmation I am as happy as anyone can be that this is a 'classic' Siberian Chiffchaff.

Ringing totals for the morning with retraps in brackets:
Lesser Redpoll 15 (6)
Willow Tit 1 (1)
Chiffchaff (tristis) 1
Robin 1
Reed Bunting (1)
Total 18 (8)