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.

Where do our wintering Blackcaps come from and why?

Over the next three winters, a new study focusing on Blackcaps wintering in Britain and Ireland will help reveal how novel migratory changes arise and spread.  The study will look at genetic and morphological differences between breeding populations and migration strategies, as well as investigate aspects of wintering behaviour, movements and survival of individuals wintering in Britain.

Up until 50 years ago, wintering by Blackcaps in Britain & Ireland was quite unusual, but numbers have since increased considerably, with many thousands now counted each winter by BTO Garden BirdWatch. Gardens are favoured sites where a combination of ‘natural’ berries and fruit along with specially provided fat, seeds, cake and pastry is the main attraction, often fiercely defended by some individuals. 

Male Blackcap. Photo by Greg Conway.

Typically, the majority of Blackcaps breeding in northern Europe migrate to the Mediterranean region for the winter. However, this is changing – some of these birds may now be migrating in a north-westerly direction to the British Isles instead! These changes appear to be facilitated by milder winters and the abundance of food provided by people, according to research carried out using Garden BirdWatch data.

A number of studies have suggested that our wintering birds come from central Europe (southern Germany/Austria), but the small number of ringing recoveries available (see map below) indicates that many may originate much closer to home, or even be resident!  Unfortunately, few recoveries confirm movements between the breeding and winter season.


Origins of ringed Blackcaps wintering in Britain and Ireland and their locations from the breeding season (red), autumn (blue) and spring (grey) (Migration Atlas – Wernham et al 2002).

To improve our knowledge of migration and breeding origin, a number of wintering Blackcaps have been fitted with Geolocators (accurate to around 70km).  These will reveal where they spend the summer, but only once re-caught back at their wintering sites.

Female Blackcap fitted with a geolocator. Photo by Greg Conway.

Colour ringing allows individuals to be identified with unique combinations and this will be used to learn more about winter behaviour, movements and use of wintering sites in Britain, which is surprisingly little understood.  Some appear to remain in the same garden all winter, but others do not!

Male Blackcap with unique colour rings. Photo by Greg Conway.

We would be very grateful for your help with the following:
Blackcap sightings - If you have wintering Blackcap in your garden please let us know and report your counts using BirdTrack or consider joining Garden BirdWatch.

Colour ring sightings - Please report all observations to: blackcap@bto.org

Ringers – Help with catching and colour ringing more Blackcaps over the coming winters would be much appreciated.  If you don’t have sites with Blackcap we can provide details of local sites where ringing is required.

To find out more about getting involved please contact: blackcap@bto.org

Greg Conway (BTO) & Benjamin Van Doren (Oxford University)
This study is collaboration between Oxford University, BTO, Exeter University and the Max Planck Institute for Evolutionary Biology, Germany.

Crossbill, Avocet or Wrybill?

Beak deformities in wild birds are unusual, with fewer than one in 200 adult birds thought to be affected. As long as the bird can feed and preen once a bill is deformed enough that the tip isn't constantly worn away, it can grow to amazing lengths.

Juvenile Blue Tit with the a bill deformity. Ipsley Alders Nature Reserve, Mike Barstow

Whilst ringing at Ipsley Alders Nature Reserve, Redditch, Mike Barstow retrapped a Blue Tit on 25/11/2013 that he previously ringed on 19/01/2012 with no deformity noted. This bird now had a severely deformed bill (below). The bird appeared healthy with good plumage, muscle and even had a trace of fat. There are therefore two birds (above and below) that have been recorded at this site which have developed a beak deformity within a few years.The research continues.

Adult Blue Tit. Ipsley Alders Nature Reserve, Mike Barstow

Measuring bill length to investigate growth rate for future captures- Mike Barstow

 Types of beak deformities in the wild:

• Crossed mandibles: similar to that of a Common Crossbill perhaps caused by slight asymmetry of the jaw. Straight beaks have been recorded as a deformity in Crossbills.

• Decurved upper mandible: can occur when the tip of the lower mandible is damaged so that the beak does not close correctly.

• Upcurved lower mandible: may occur when the tip of the upper mandible is missing (i.e. broken off).

• Elongation of both mandibles: produces ‘Curlew-type’ beaks, although the degree of curvature varies considerably between individuals.

• Bent to the side: seemingly uncommon, with one or other mandible warping sideways.

• Gapped: where the upper and lower mandibles do not close fully leaving a visible gap.

For more information click here

The future’s bright - the future’s green

I remember the exact day that I became hooked on birds. I was four years old and my family had just moved to North Norfolk. My Dad, Tony, a biology teacher who is interested in all things natural history, went with a colleague to see a male Hen Harrier that had been roosting on Kelling Heath and I tagged along. I’d been looking at birds in the garden for a year or two previously (and have the check-list, full of terrible spelling mistakes and even more horrendous misidentifications to prove it), but this was definitely the point of no return; fast forward 35 years and I am now a qualified ringer and keen nest recorder who has the privilege of working on birds for a living as a BTO staff member.

Male Hen Harrier - the species responsible for Dave writing this post. Copyright Martin Bennett

  

The path from hobby to career was fuelled by many things. The proximity of the Norfolk Wildlife Trust’s Cley reserve, just four miles north of my home, did no harm in terms of reinforcing my interest, as did the endless streams of high quality documentaries, particularly those featuring the soporific tones of David Attenborough, which were compulsory viewing in my house. It was people who made the real difference, though – parents (my Mum, Barbara, still collects Blackbird colour-ring resighting data for me), teachers (Dave Horsley and Ralph Wiggins deserve special mention) and friends (Gav Horsley and Nick Acheson in particular) who tutored me and, equally importantly, transported me to the local hotspots. OK, so I didn’t have access to the wonders of the internet, but then I didn’t have the distractions of it either.

Dave's Mum Barbara has been collecting colour-ring resighting data on individually marked Blackbirds in her garden almost every day since March 2007

But this post isn’t about me as I’m rapidly becoming the past; it’s about the future, and that future is looking a little greener. A few days ago, Lorraine Miller directed me to an article on the wonderful A Focus On Nature website, an essential networking tool for any aspiring young conservationist. The piece was a focus feature on five naturalists, aged between 9 and 13, including Lorraine’s daughters Abby and Evie. I already knew that Team Miller were contributing to the BTO’s Nest Record Scheme, but I was still amazed at the wealth of other surveys that were mentioned. Four of the five folk highlighted are already training to ring, including prolific bloggers Toby Carter and Findlay Wilde, or seeking trainers (and the photo of the fifth, Harley Wilde, sees him holding a bird at a ringing demo) while Garden BirdWatch, BirdTrack and the Winter Thrush Survey all feature.

Ringing demonstrations are a great way of sparking the conservation interest of the next generation, whether they go on to be ringers or not

This makes me a bit of a late-starter. While I was birding at four, I twitched away my teens and it wasn’t until I hit my mid-twenties that I started actually making a real contribution to conservation by participating in surveys. These guys have got a decade on me already, and most of them didn’t have the luxury of doorstep nature reserves or teachers with time to spend on after-hours activities. These are fast-tracked conservationists and, with green issues seemingly at their lowest ebb on the political agenda, we need them now more than ever.
Dave Leech
Head of BTO Nest Record Scheme

Trichomonosis insight

The impact that diseases have on bird populations is a fascinating topic of research, to which ringers and members of the public can contribute. Many will now be aware of the detrimental effect that Trichomonosis has had on Greenfinch populations in the UK, a relationship established by a piece of research led by scientists at the Institute of Zoology in London and the BTO. A subsequent study from the same team also showed, through molecular analyses, that the disease arrived in Fennoscandia from the UK in 2008, most likely carried by Chaffinches. This link was identified thanks to the known migration route of this species provided by previous ringing data.

Greenfinch showing signs of Trichomonosis by Heather Povey

A project by different authors has recently showed that Trichomonosis spread in Finland in 2008 and 2009 and impacted local Greenfinch and Chaffinch breeding populations. In August-September 2008 the first cases of this disease had appeared in the country, followed by a peak in reported mortality in July 2009, although cases diminished in 2010 to pick up again in 2011. The Finnish study showed that population of breeding Greenfinch declined by 47% in south Finland, but not other parts of the country, at the peak of the outbreak between 2009 and 2010, whilst Chaffinch declined by 4%, between 2006 and 2010, the first population decrease since 1984. Bird body condition was also affected by the disease. Ringing data highlighted that Greenfinches, especially juveniles, were lighter than usual over the autumns 2008 and 2009 in the areas most affected by Trichomonosis.

These studies are a very good example of the important contribution to science that members of the public and ringers provide by reporting changes in birds and garden wildlife, as well as the unique high-quality data and essential information that ringing provides.

For more background information, visit the BTO GBW webpage

Daria Dadam, Research Ecologist