Return of the winter Blackcaps - a geolocator story

How do migratory birds respond to a changing environment? The answer to this question may help us unlock key insights into the mechanisms behind migration, and predict how animals will adjust to future global change. British Blackcaps may provide key insights into birds’ abilities to evolve changes in migration. Blackcaps are now spending the winter in the Britain and Ireland in greater numbers than ever before - a change BTO scientists have linked to garden feeding and warmer temperatures. But what exactly do they gain by wintering here, and where are they coming from?

Blackcap with first geolocator retrieved - photo by Benjamin Van Doren

As previously reported, last year, researchers from the BTO, Oxford University, and Exeter University began teaming up with bird ringers and garden owners across Britain and Ireland to study the Blackcaps that visit our gardens in winter. Last winter, we fitted 36 Blackcaps with geolocators, miniature devices that track movements throughout the year; however, the birds must be recaptured in order to retrieve the device and data, which can be a challenge.

Excitingly, returning Blackcaps carrying geolocators have been seen in gardens around the country since late November. These early successes would not have been possible without the dedicated BTO ringers, Garden BirdWatch participants, and other volunteers who have contributed so much time and effort to the ongoing study.

Blackcap geolocator movements. Blue dot - wintering site.

On 26 November, Glynne Evans recaptured the first returning individual in his Hampshire garden where it was tagged nine months earlier. Preliminary analysis indicates that the bird left Britain at the end of March and spent the summer in France, before returning by early November. But is this pattern the exception, or the rule? And why did this bird decide to come north for the winter when it was already in southern France? We hope to find the answers to these questions and many others - as the project continues.

Garden ideal for Blackcaps - photo by Benjamin Van Doren

Glynne’s GBW garden has turned out to be an exceptional Blackcap site, with a further tagged bird (analysis in progress) being caught in December, as well as two other colour-ringed birds returning from last year, giving a return rate of 25%, so far. We know very little about their behaviour and movements in winter, so any sightings of colour-ringed birds would also help answer these questions. Glynne provides food for Blackcaps starting relatively early on in autumn—could this partially explain their affinity for his garden?

How can you help? 

Do you have Blackcaps visiting your garden in winter? Look out for Blackcaps with colour rings and note the positions of the colours on each leg, or even better, take a photograph. Observers interested in joining the colour-ringing and tracking efforts can contact Benjamin Van Doren at Oxford (benjamin.vandoren@zoo.ox.ac.uk) or Greg Conway at the BTO (greg.conway@bto.org). Gardens with multiple Blackcaps regularly attending bird feeders are particularly valuable. For further information please see Life Cycle, issue 6 Autumn 2017.

This study is a collaboration between Oxford University, BTO, Exeter University and the Max Planck Institute for Evolutionary Biology, Germany.

Exceptional Siskin Surge

The Siskin movement this autumn has been exceptional, for both the early start and vast numbers involved, as indicated by BirdTrack. With the peak movement and arrival of continental birds still to come, numbers in the UK are expected to increase considerably.


BirdTrack Siskin reporting rate

Jeff Kew from Thetford, Norfolk writes:

This has been an exceptional September for Siskins in the UK, with large numbers being reported across southern Britain, due to a major irruption from Northern Britain.

Last autumn Siskins were fairly scare in Southern England with a few being reported on feeders in February and March, the usual peak time to see and ring this species. Reports from Scotland indicate a bumper cone crop last summer and consequently most Siskins stayed at home for the winter, this Autumn with dwindling food supplies the picture is very different.

In the Norfolk / Suffolk Brecks area we have not seen anything like the numbers coming to feeding stations in September since 2005.

In our Thetford garden we have already ringed 611 Siskins this month (in just 4 ringing sessions), with an amazing 368 caught on the 18 September.

One of the hundreds of Siskins recorded taken by Jeff Kew

We have had birds ranging from exceptionally light (10.4g) to exceptionally heavy (17.0g) - which presumably indicates a mix of recently arrived birds and birds with serious intent to travel much further south. The majority are juveniles, which appear to have done less post juvenile moult than our local breeders.

Post juvenile moult strategies are interesting with the amount of post juvenile moult being variable and probably linked to both fledging date and food supply. We believe unmoulted juveniles (3JJ) can reach us from Scotland.

Thinking back to what we saw in 2005 we had high numbers through September, followed by two recoveries in Spain in Navarra and on Mallorca - which could give an indication of where some birds of this years birds may end up this winter.

Greg Conway from Thetford Forest Ringing Group writes:

The extent of post juvenile moult is highly variable, with some typically retaining one, or more, old greater coverts along with juvenile tertials and tail feathers, whereas others replace all coverts, tertials and tail (see below).  However, there are also many in between that replace different numbers of tertials and tail, often symmetrically but not always centrally!

Juvenile Siskin with replaced greater coverts, tail and tertials - Greg Conway

Juvenile Siskin with replaced greater coverts and two inner tertials - Greg Conway

Juvenile Siskin that has replaced outer pair and 2 central pairs of tail feathers contrasting with juvenile feathers (pointed and browner) - Greg Conway

To better understand the mix of different migration and post juvenile moult strategies occurring this autumn, and add to long-term data collected from Thetford Forest, ​any ringers catching Siskins are encouraged to record the following biometrics (in addition to age/sex, wing & weight):

All birds if possible!
1) Number of unmoulted greater coverts (including those with zero)
2) Fat score (0-8 scale)​

And if time allows!
3) Tertial moult (record in IPMR moult card)
4) Tail moult (record in IPMR moult card)
5) Pectoral muscle score (0-3 scale)

Quail surprise!

Ringer Greg Conway writes:

When one of my trainee ringers, mentioned that he had a 'good number' of Quail on a local farm in south Norfolk, and recalling the apparent ease with which this species is caught in Belgium and the Netherlands, I decide to give it a try. However, given the low success rate when attempting to catch in the autumn, I didn't expect to to catch any. Just another exercise in put nets up and taking down again.


So on 11th June, just as the sun was setting, we carefully put up a triangle in a cereal crop. By the time the nets were set, up to 4 males were calling nearby and we got the impression that something was watching us! As I made a final check of the net I was totally amazed to watch a male pop up from within the triangle of nets and jump into the net. It was immediately extracted and processed, then I started the tape lure (having the appropriate tape luring licence) and a female immediately flew into the net and again was promptly extracted. It was an hour later though before the third and final Quail of the evening was caught.

If that wasn't reward enough, I was amazed to receive notification recently that one of the three was shot in September at Montegut-Arros, Midi-Pyrenees, France.

Four Quail were ringed in Britain & Ireland in 2010 and we are up to 7 so far this year. It will be interesting to see how many were ringed this year, once all the data is in our database.

Thanks to John Secker for the photo.

CES ringers finally get a lie-in

Greg Conway writes:

As the breeding season draws to a close, so the hundreds of dedicated ringers who run the 120 Constant Effort Sites (CES) scattered across Britain and Ireland can start to relax and recuperate after a summer of early morning starts. As they use the same mist nets in the same places each year to catch the birds, the information they collect tells us about changes in numbers of adults and juveniles over time, so abundance, breeding success and survival can all be measured, making this one of the most valuable ringing projects.

Target species include many of our long-distance migrants (e.g. Reed Warbler, Sedge Warbler, Garden Warbler, Whitethroat, Willow Warbler) plus resident scrub species such as Wren, Dunnock, Blackbird and Robin.

The CES scheme started in 1983, so ringers have just completed the 29th season and will soon be focussing their attention on getting all their data to BTO HQ ready for analysis. The results of the most recent CES analysis can be found on the species pages here and the preliminary results from 2011 will be available later in the autumn. These will provide the first indications of abundance and breeding success of birds nesting this summer, helping to assess the potential impact of yet another harsh winter.

Early indications suggest that a number of migrant species have returned in greater than usual numbers. However, despite an early start to the breeding for many species, prolonged periods of cool and wet weather, particularly in the north and west of Britain and Ireland, were associated reduced breeding productivity levels.

A big thank you to everyone whole has help with CES this year and those ringers who have already submitted their data.

Thanks to Dorian Moss for the above picture of Lucy Yates and Kate Risely for the top picture of Nick Moran.