Saturday, 19 August 2017

Billinge 13th & 16th August: mixed weather and mixed results.

Decent weather has been at a premium this August so it has been a case of trying to get out ringing whenever conditions and circumstances allow. The 13th provided one of those opportunities and produced a catch of 50 new birds with Willow Warblers and Chiffchaffs making up half the total. Willow Warblers topped the totals with 18 ringed, their highest total of the month, but the juvenile:adult ratio remained quite low at 2.6:1 (13 juveniles to 5 adults). At the other end of the scale only 1 Tree Pipit was ringed which was very disappointing as we are approaching peak passage for that species and only 4 were seen all morning, on the other hand the capture of a Spotted Flycatcher was a very nice surprise as they are a very scarce passage migrant these days and it's even rarer for one to find its way into a net.


Spotted Flycatcher

Spotted Flycatcher 13/08/17 - the only record of the autumn so far.
Ringing totals for 13/08/17 were: Goldcrest 2; Blue Tit 5; Great Tit 2; Coal Tit 1; Chiffchaff 7; Willow Warbler 18; Blackcap 3; Whitethroat 1; Blackbird 1; Spotted Flycatcher 1; Robin 1; Tree Pipit 1; Chaffinch 3; Bullfinch 3; Lesser Redpoll 1.

The 16th turned out to be a fairly quiet day with many birds having departed since my previous visit and precious little coming through to replace them. Only 25 birds were ringed which is below the average for mid-August. There was a bit of movement overhead with a party of 5 Snipe flying high to the north (the first record of the autumn) and a total of 9 Tree Pipits flying south (the second highest total recorded this autumn) being the best of what little there was. Warblers were in short supply and only 5 Willow Warblers were ringed which suggests they have passed their peak. The proportion of juvenile Willow Warblers continues to be unusually low with just 3 of the 5 ringed being youngsters. Two of the Chiffchaffs ringed were interesting in that they had completed their post juvenile moult and this should signal an increase in the numbers migrating through the site from now on.

Chiffchaffs can start migrating in earnest once they have completed their pj moult.
Ringing totals for 16/08/17 were: Goldcrest 2; Blue Tit 2; Chiffchaff 5; Willow Warbler 5; Blackcap 2; Whitethroat 2; Tree Pipit 4; Chaffinch 2; Linnet 1.

Tree Pipit - one of four ringed on the 16th.


Saturday, 12 August 2017

Billinge 10th August 2017 - more on Willow Warblers

Well, buy me a flat cap and call me Victor because I am bringing up the subject of Willow Warblers and age ratios again. Another ringing session at Billinge on the 10th resulted in a catch of 42 birds that included 11 Willow Warblers, 7 of which were adults. I didn't know what to expect given the complete absence of juvenile Willow Warblers in the previous day's catch but I didn't think adults would outnumber juveniles by almost 2:1. It increasingly looks like Willow Warblers have had a very poor breeding season and I can't see the situation improving unless there have been a lot of successful late broods and those juveniles have yet to come through.


Eye colour can be used to help age Willow Warblers in autumn. Adults have a brown eye approaching chestnut colour like the bird on the right whilst the eye colour of juveniles is much duller and greyer like the bird on the left. I have not used this feature prior to this autumn but it appears to be very reliable from what I have seen so far and is well worth using in conjunction with the usual plumage features. It wasn't easy to photograph but is fairly easy to see in the hand with the naked eye, although some may find use of a low magnification hand lens helpful.
Willow Warblers are generally single brooded and although they are amongst the first of the summer visitors to arrive they have a pretty tight schedule as autumn migration peaks towards the middle of August and the adults also have to fit in a complete moult. The schedule is so tight adult Willow Warblers may start to moult before they have completed breeding, they also moult quite quickly and they often start migrating before the moult is complete. That tight schedule limits the opportunity for late broods (be they second broods or repeat nesting attempts following earlier failures) which means the chances of there being a surge in juvenile numbers from them is really quite low.

While there is evidence that climate change is causing some summer visitors to arrive a little earlier and depart a bit later than they used to it doesn't mean the duration of stay of individuals is getting significantly longer nor does it mean the timing of migration has changed significantly for the bulk of the population. Willow Warblers that arrive a little earlier may simply be amongst the first to leave and those that stay later are more likely to be juveniles and they may also be compromising their survival chances by a later departure. It certainly doesn't look like climate change is extending the breeding season for Willow Warblers or likely to lead to an increased occurence of second or late broods.

Whilst climate change may be extending the spring and autumn periods the major impact on Willow Warbler productivity is caused by the weather during the breeding season, and the levels of rainfall in particular. It is not just the amount of rainfall that matters but also its intensity that can make all the difference when it comes to breeding outcomes and more intense rain is one of the consequences of a warming climate. Met Office statistics show June 2017 has been amongst the wettest on record, with the UK as a whole having 50% more rainfall than average. Whilst North Merseyside wasn't one of the worst affected areas in terms of increased rainfall it did experience some intense downpours that could have led to increased nest failures and increased mortality of recently fledged young. Parts of northern England and southern Scotland have received more than twice the normal June rainfall and that could have had an even bigger impact on productivity in those regions. 

Juvenile Willow Warbler 10/08/17.
This recently fledged juvenile had only just started its post-juvenile moult and must have come from a late nesting attempt. Their fluffy juvenile plumage probably doesn't provide much protection from prolonged or intense periods of rain.
So it seems to have been a wash out for Willow Warblers this year and while there may be some regional differences I suspect the overall picture will show productivity is below average and well below that of last year. The higher number of adults caught in July may have been due to a high incidence of failure late in the nestling stage as that wouldn't have left enough time for those adults to make another breeding attempt. Such failed breeders may have started migrating a little earlier as a result.

Other ringing highlights from the 10th were: a young male Sparrowhawk, the first of the autumn; another 5 new Goldcrests bringing their August total to 14 and autumn total to 33 which is well up on last year; 2 Tree Pipits from at least 12 seen which is the first double figure movement of the autumn and fairly typical for the date.


This young male Sparrowhawk had the odd remnant of down on the tips of  some of the feathers of the mantle.

I love Tree Pipits.
Ringing totals for 10/08/17 were: Sparrowhawk 1; Goldcrest 5 (1); Blue Tit 4; Great Tit 2; Coal Tit 1; Long-tailed Tit 4; Chiffchaff 3; Willow Warbler 11; Blackcap 1; Whitethroat 2; Wren 1; Song Thrush 1; Tree Pipit 2; Goldfinch 1; Yellowhammer 1; Reed Bunting (1).

Wednesday, 9 August 2017

'I don't believe it!'

I had a Victor Meldrew moment this morning, in fact I had several of them. The weather forecast for this morning wasn't brilliant but the rain cleared about a hour after sunrise and I ventured up to Billinge despite the stiff northerly breeze. I mainly wanted to see if any Tree Pipits would start to move after the rain had gone through but also took opportunity to put up a couple of nets in the sheltered rides of the NE corner of the site while I was there.

There didn't appear to be any Tree Pipits moving or much else for that matter and there wasn't much moving around in the bushes either. It was a surprise, therefore, to find a Tree Pipit in one of the nets on the second net round but that wasn't one of the 'I don't believe it' moments. The second net round also produced a single Willow Warbler and interestingly it was a new adult. Regular readers of this blog will know that I have been catching more adults than usual this autumn so catching another adult wasn't a huge surprise. When the next Willow Warbler also turned out to be a new adult I simply thought it was just one of those things that can happen by chance and that I would catch some juveniles in subsequent net rounds.

The catching rate was very slow but when the 3rd Willow Warbler of the morning also turned out to be a new adult I did start to think 'I don't believe it' and I may even have said it out loud. The next net round produced yet another adult Willow Warbler and another 'I don't believe it', this time the bird was a retrap that was last caught in April of this year. At that point I still thought I was likely to catch at least a couple of juveniles before I packed up because a catch that only included adults seemed so unlikely as to be unthinkable. When the penultimate net round produced another new adult, the 5th of the morning, it produced another 'I don't believe it' from me. The final net round drew a blank so it was a case of 5 adults out of 5 and not a juvenile in sight!.

I know its not a big sample but to catch 5 Willow Warblers on 9th August and for all of them to be adults is exceptional to say the least. It certainly underscores how unusual the juvenile:adult ratio has been at the site this autumn and I am sure it is a subject I will come back to again at some point.


Adult Willow Warbler 09/08/17. Four of the five had completed their full moult and the one that was still in moult had nearly finished.
Ringing totals for 09/08/17 were: Chiffchaff 2; Willow Warbler 4 (1); Blackcap 2; Tree Pipit 1.

Sunday, 6 August 2017

Billinge 6th & 7th August: First Tree Pipits

It is that time of year when I expect to get my first Tree Pipits of the autumn and I wasn't disappointed with 1 ringed yesterday and another 3 today. None of them announced their presence by calling before they were caught and I didn't see any of them drop in as I usually do when passing birds are attracted to the audio lures. A total of 3 were seen yesterday but the 3 ringed today were the only ones recorded. Over the last 3 years the first autumn sighting has been between the 1st and 7th of August so yesterday's birds were pretty much bang on time.


Tree Pipit 06/08/17
Other highlights from the 2 sessions were the capture of 4 Garden Warblers and 5 Whitethroats; the latter qualifying a highlight because I only managed to ring 1 Whitethroat in the whole of July. Another 6 juvenile Goldcrest supports my previous comments about the species having a productive breeding season. Goldcrests have a long breeding season and many pairs are probably still churning out more young so it may turn out to be another bumper year.


Garden Warbler 06/08/17
Ringing totals for 05/08/217 were: Goldcrest 3; Blue Tit 18; Great Tit 2; Coal Tit 1; Chiffchaff 3; Willow Warbler 17(4); Blackcap 3; Garden Warbler 3; Whitethroat 2; Wren 1; Blackbird 1; Tree Pipit 1; Chaffinch 2; Bullfinch 1. Total 58 new birds and 4 retraps.

Ringing totals for 06/08/17 were: Goldcrest 3; Blue Tit 3; Chiffchaff 2, Willow Warbler 8 (2); Garden Warbler 1; Whitethroat 3; Wren 1; Song Thrush 2; Robin 1; Tree Pipit 3; Bullfinch (1); Goldfinch 1. Total 28 new birds and 3 retraps.

Thursday, 3 August 2017

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.