Up-country warblers and a lesson in coverts

We recently received details from the BTO of two warblers caught on our penultimate CES ringing session at Gunwalloe on 16th August, both originating from up-country. Reed Warbler D992026 was ringed at Squire's Down, Dorset, on 11th August so had made the take just five days to make the 230km trip down to Cornwall. It almost certainly did it in one go though, and had also had time to put on some pre-migration weight, fattening from 11.2g to 12.4g in those five days.

An altogether different bird was Sedge Warbler Y941821, ringed at Icklesham, Sussex, on 6th August 2013. You then wonder if this bird chose different autumn migration routes as a juvenile and adult, now coming further west, or was this just coincidence.

The only other ringing of late has been a bit of garden ringing for new trainees, but it's always good to catch some instructive birds. The Blue Tit below very nicely shows the contrast between retained juvenile coverts (dull greeny-blue) and moulted adult-type coverts (blue). This bird had moulted all bar one of its greater coverts, the carpal covert and just the smallest alula feather, so see if you can identify them all in the pic!

Think we'll be able to identify this Dunnock without recatching it!

As an aside, I also dropped into Devoran before high-tide in the evening to check the roosting Curlews, to find two colour-ringed birds. We think the below might be a Scottish bird (the single yellow ring was coded BI) and the other bird looked German, but refused to stand on more than one leg in all the time I was sat watching!

Why so many adult Sedge Warblers?

We've noticed this month that we seem to have been catching more adult Sedge Warbles than normal, so we thought we'd have a look back through our data from previous years and see if this is correct... So we compared the percentage of adults in our reedbed catches at Marazion/Gunwalloe and also at the migration site at Nanjizal.

We couldn't find a photo of adult/juvenile Sedge Warblers side by side,
so this wing shot of will have to suffice,
but the difference in wear on the flight feathers is obvious,
hence these birds are easy to age

 So the August percentages look like this (with total number of birds caught in brackets)...

	Gunwalloe/Marazion	Nanjizal
2011	10% (375)
2012	16% (125)
2013	8% (198)	7% (215)
2014	12% (87)	8% (657)
2015	24% (128)	15% (907)

From this cursory glance at the data it looks like we were in fact correct, with a much higher percentage of adults in our catch this autumn. Why this might be is a bit of a mystery and it'll be interesting to see how this compares to other sites in the southwest and beyond.

Reedbed roost and ruins

With a small break in the weather we finally managed to fit in a CES session at Guwalloe Marsh on Saturday, so while we were there we did a Swallow roost in the reedbed the night before. With well over a thousand Swallows gathering, the birds looked good, the weather looked good and we had our first big Swallow catch of the autumn.

After a long night processing, we ended up with 174 Swallows (inc 14 adults), four Sand Martins and some odds and sods, so a good (if late) start to the hirundine season.

Swallows ready to be processed and put to bed in our roost box

Poor night-time pic, but nice comparison of adult and juvenile Sand Martin

And an even worse photo of them going in the morning!

We followed the roost up by sleeping over by the marsh and then getting up for CES in the morning. The weather was kind for a change and with an extra net the final total of 89 birds was pretty acceptable, including 32 Sedge Warblers and 14 Reed Warblers. Only 69 of these were from standard nets, but this total is our highest ever for Visit 10.

What was apparent was that birds were already fattening up for migration, with several Sedge Warblers carrying lots of fuel: compare the Fat 0 bird weighing 9.1g to the Fat 7 bird weighing 16.7g and you'll get the idea. It was also interesting that it was the adult birds that were the fattest, with the average juvenile weight being 10.8g compared to 13.1g for adults.

Yet another dire photo, this time of a Fat 7 Sedge Warbler

Just to add a bit of culture to the day, we also stopped off to have a nose round the ongoing archaeological dig on the clifftop. The site is a mediaeval settlement and would have been the largest in the Kerrier area, so a bit of a change from the single farm and holiday shop here now! But with some fascinating archaeology on show it was a rather interesting aside...

Apparently these are two walls of an old iron age building

Last CES for 2014

This morning saw three of us running the last CES visit of the year at Gunwalloe. The day dawned pretty cold and wet, so we weren't overly optimistic for a big catch... But in the end, the total of 27 birds was the most we've ever had on the last visit, ranging from 13 to 21 in previous years. This continues the trend of having much better catches late in the season this year...

Dawn over the reedbed at Gunwalloe

Visit totals on CES since 2011

Most of the catch were Sedge Warblers, a surprisingly large number of which were carrying plenty of fat. The heaviest was an adult weighing in at 17.2g, compared to a juvenile of similar size with no fat that weighed 9.4g!

Bit hard to see, but this is a Fat 7 Sedge Warbler (on a scale of 0 to 8)

The difference in wear on flight feathers between juvenile (left)
and adult (right) Sedge Warbler is pretty obvious!

Numbers of Sedge Warbler were the lowest since we started the CES in 2011, with Reed Warblers also pretty low in number. 

	2011	2012	2013	2014
Reed Warbler	184	108	115	110
Sedge Warbler	115	69	77	60
Cetti's Warbler	15	3	1	3
Total catch	533	235	257	226

Apart from Sedge and Reed Warblers, the only other bird of note was a juvenile Cetti's Warbler: a species that hasn't done too well at Gunwalloe over the last few years. Compare numbers on the CES in 2001 to those the last three years!

Finally, thanks to everyone that's helped out with the CES this year and it's been pretty grim at times, especially on the so-called 'wet ride' which turned into more of a swamp than anything else over the last few visits...

The notorious Gunwalloe 'wet ride'

Fault bars and a mystery feather

A good-sized team congregated this morning to run Visit 8 of the CES at Gunwalloe, in perfect conditions. A few hundred Swallows coming out of roost near the nets gave us a few stragglers (including an adult we'd ringed at the roost last week), but the majority of the catch was, predictably, Reed Warblers. The final total of 55 birds caught was close to the visit average of 60 birds, including the welcome return of a few Sedge Warblers, the less welcome return of reedbed Blue Tits and a lone juvenile Cetti's Warbler.

Symptomatic of a spell of poor weather a few weeks ago, we caught two birds both showing really obvious 'fault bars' in the tail. These occur when a period of reduced food supply in the nest means that growing feathers are lacking substance, so show up as weak bars along the tail: akin to tree rings in fact. The fact these bars are all the same distance from the tail tip indicates that these tail feathers were all grown all at the same time (ie in the nest), so is a very good indication these birds are juveniles.

Sedge Warbler fault bar

These fault bars are obviously also weak points in the feather and in this second example you can guess that the bird will be left with a rather stubby tail in the not-too-distant future... Not a problem if you're a local resident, but rather more of a problem for a long-distance migrant.

A rather more extreme fault bar on a Blue Ti

Heading back to the cars we also spotted this rather unusual feather, so any guesses as to it's identity please post a comment...

Commuting Storm Petrels and warblers

We recently received some interesting recoveries from the BTO, mostly of some pretty fascinating Storm Petrel movements. In the past we've traded quite a few birds with Ile Banneg, home to France's largest breeding population of Storm Petrels, but these reports were notable.

Over summer 2013 at Hot Point, Lizard, we only caught one French-ringed Storm Petrel (compared to four in 2012), but we've just heard that we had a great run of records of birds going the other way. In total five birds ringed at Hot Point in 2013 were recaught on Banneg later in the year, with a further bird ringed in 2012 unfortunately found predated there. This compares with just one going that way in 2012.

But what was interesting was when these birds were caught, with some making very quick movements over the 178km to Banneg. Birds ringed in June were recaught 35 days, 32 days and four days later, whilst a bird ringed in July was recaught three days later and one ringed in August was recaught the next day! I'm sure birds regularly commute backwards and forwards across the English Channel, but in theory non-breeding birds are more attracted to tape lures, but I bet these movements are of breeding birds...

We also just received details of a few movements from last autumn, including a Sedge Warbler ringed at Marazion and recaught in France five days later (but it did weigh 11g when ringed so was obviously getting ready for the off), a Spanish-ringed Reed Warbler recaught at Gunwalloe was ringed on spring migration (the first to be found in Cornwall), and a Chiffchaff we caught in November had been ringed in North Yorkshire a month earlier. This bird had come over 500km and was presumably on migration through the country when ringed.

The map below shows where these birds were ringed/recaught: Storm Petrels (red), Sedge Warbler (green), Reed Warbler (blue) and Chiffchaff (yellow). 

Mauritania Sedge Warbler and a Cormorant caught in the act

We recently received a whole bunch of reports back from BTO of birds we'd either ringed or recaught ourselves. The map below shows the spread of these reports and gives a good overview of where the birds we're ringing/seeing are coming from and going to. The map below shows birds ringed by us found elsewhere (in red) and birds ringed elsewhere recaught/seen by us (in blue), and you can zoom in to see more detail. Clicking on a line will also give you the full details for the movement: species, dates, places...

View Recent recoveries 2013 in a larger map

The furthest movements are a Sedge Warbler ringed at Gunwalloe recaught by French ringers 2400 miles away in Mauritania and a Polish-ringed Mediterranean Gull seen on the Hayle estuary (along with a Channel Islands Herring Gull). The movement to Mauritania is expected as this is where Sedge Warblers go, but is still only thew second from Cornwall to Mauritanis, with fewer than 25 BTO-ringed birds found there!

Other long-distance movements include Storm Petrels in all directions, with two birds to Skokholm Island (expect more from here as ringing has started a fresh here) and birds recaught from the Channel Islands and Co Wexford. We've also now got all the details back on the various colour-ringed Kittiwakes now breeding in Cornwall (more info on these here). These are all from the same French colony, but the interchanges are proving pretty fascinating!

View Recent recoveries 2013 in a larger map

A bit closer to home, a couple more of our colour-ringed Herring Gulls have been seen. Another bird from Falmouth visited Stithians Reservoir and a bird from Rinsey Cliffs was seen on the beach at Marazion. These birds all have a blue ring with code W:000 to W:999 so keep an eye out for these around the coast or at any gatherings of gulls. Another of our colour-ringed birds reported was a Cormorant caught in netting whilst stealing fish from an inland fishery, but was happily untangled and released unharmed. Wonder if it's learnt its lesson??

We don't have a photo of Cormorant TAH caught at the fish farm,
but here's TAB also ringed on Mullion Island

One final interesting movement is a Sedge Warbler ringed at Nanjizal and then recaught five days later at Gunwalloe, almost directly due east. We've also had recent reports of some of our Sedge Warblers moving north in autumn, so I wonder if these are actually heading out of the country somewhere further east and not directly or through the Isles of Scilly as expected...