15 August 2016

An unexpected but timely recovery

Gary Clewely (BTO) writes:

Nightingales are one of the best-known species in the UK for their impressive vocalisations, yet will be increasingly unfamiliar to many of us due to a marked range contraction and population decline in recent decades.

The motivation behind the BTO Nightingale tracking study is to identify key migratory routes and wintering areas to inform conservation. Fieldwork during the 2016 Spring was particularly exciting, because in addition to retrieving geolocators from previous years, this was the first time GPS loggers weighing less than 1 g were fitted to Nightingales in the UK, which if recovered the following year would give us unparalleled data on their migration.

Nightingale. Photo taken by John Spaull

During a mist-netting session at Alton Water (blue pin on map), in Suffolk (managed by Anglian Water, one of the tracking study partners) where we were catching males for tagging, one of the birds caught was already carrying a BTO metal ring – NA82699. This was initially not too unusual, especially as ringing was taking place on the site. The bird was swiftly processed and fitted with a GPS tag before being released safely back into its territory. Later, it came to light that NA82699 had in fact been ringed in January 2016 during an expedition to the Kartong Bird Observatory in The Gambia (orange pin on map). This is the first case of a Nightingale ringed in sub-Saharan Africa being found in the UK but remarkably, it is not the first exchange of Nightingales between East Anglia and the Kartong survey area. In 2011 and 2012, Nightingales ringed in East Anglia were recorded in Kartong, including a bird originally from a site near Ipswich, just 10 km from Alton Water.

Of course, recoveries in and from Africa are hugely dependent on effort and are biased depending on where ringing activities take place. Nonetheless, it is extremely encouraging that the ongoing monitoring at places such as the Kartong Bird Observatory is valuable and well placed to help inform us about migrant bird populations.

Olly Fox, who was on the January trip to The Gambia, reports that the Kartong ringing survey has a relatively high retrap rate for Nightingales with four birds encountered in multiple winters (in addition to the three exchanges between Kartong and the UK) from only 17 birds ringed between 201115. Olly goes on to tell me that wintering Nightingales in the coastal part of The Gambia are generally found in patches of dense vegetation but can also occupy secondary habitat, such as disused farmland. For males at least, these territories are defended throughout the winter months. However, increasingly these habitats are under pressure from development of agriculture and clearance of woodland and scrub to satisfy a rise in demand for firewood and charcoal. These are perfect examples of land-use changes occurring across the range of many migrant species that are important to identify and understand when considering their conservation.

Nightingale singing. Photo taken by Amy Lewis

Far from jumping the gun on the tracking study results, recoveries such as this complement tracking well, providing useful context and help to focus winter ringing efforts and inform local conservation, in this case by the Gambian Department of Parks and Wildlife Management and other NGOs. We will still need the detailed tracking information to understand the precise routes taken and the timing of their movements. The combination of continued tracking work and further ringing in The Gambia will help us understand how typical the apparent connectivity of Nightingales between East Anglia and coastal Gambia is.

02 August 2016

Want to see a Whimbrel? Den mark it with a colour ring

It's always a pleasure to hear the Whimbrel's distinctive call when flying over and it's very special when one is caught (see online reports). Relatively few are ringed in Britain & Ireland and with the addition of colour rings the reporting rate has increased substantially. The pie chart below shows how few dead birds are found in relation to the number of reports received of colour rings.

The Mid Wales Ringing Group started a colour ringing project in 2010 to try to answer some basic questions regarding Welsh birds in particular, like movements, staging areas, survival and site faithfulness. Some of these birds have been reported (dead and alive) in quite a few areas including Scotland, France and North Africa.

A Whimbrel wearing a Mid Wales colour-ring combination was recently reported in Denmark. The BTO online reports show this to be only the fourth BTO-ringed Whimbrel to be reported in Denmark. Yellow D74 was ringed on 30 April 2016 at 2:50 am and 72 days later it had travelled a minimum distance of 1,059 km to Storevorde, Denmark.

If you were hoping to see a BTO-ringed Whimbrel outside Britain & Ireland, there is a much greater chance of seeing one in Guinea (195 reports), Guinea Bissau (224 reports) and Iceland (366 reports).

Colour-ringed Whimbrel photo taken by Jens Veilgaard Vendelbo
Whimbrel photo taken by Jens Veilgaard Vendelbo

So if you ever see a Whimbrel, or any other wild bird for that matter, report it at www.ring.ac. The information will be very useful and could hint towards a new movement or behaviour.

For more information on this and other Mid Wales goings on, click here.

18 July 2016

Too many males?

Cat Morrison is the lead author on a new paper that, using CES data, found biased sex ratios in small migrant populations, as Cat explains:

For many of us the distinctive songs of our migrant birds are a clear sign of the start of spring, however our recent study indicates that these songs may be masking bigger problems for these species.

Using data collected by ringers we explored the spatial variation in sex ratios of Willow Warblers at CE sites. Our analysis revealed that in 1994, the male-female ratio was around 50:50 however, by 2012 males had started to outnumber females, with the male-female ratio increasing to 60:40. Interestingly, it was also clear that male-bias sites were most common in the south-east of England, where populations have recently declined and Willow Warblers are at relatively low abundances. 

Willow Warbler. Photo by Edmund Fellowes.

We wondered if it was possible that male-biased sex ratios could be due to greater female mortality in the smaller populations, where the greater costs of breeding for females may be exacerbated by poorer resources. However, although male mortality rates were lower than females, this difference was not greater in sites with strongly male-bias sex ratios. Instead, it is likely that the increase in the male-female ratio is the result of female choice, with individuals preferentially recruiting into larger populations, leaving males unpaired in the small populations. This could mean that conservation efforts will be most successful by focusing on sites capable of supporting large populations with more equal sex ratios.

Our work also has implications for how we monitor our bird species, as the higher frequency of unpaired males, singing later into the breeding season can lead to an over estimation of the breeding abundance in male-bias populations.

Further reading:
Morrison, C. A., Robinson, R. A., Clark, J. A. & Gill, J. A. (2016) Causes and consequences of spatial variation in sex ratios in a declining bird species. Journal of Animal Ecology. doi:10.1111/1365-2656.12556

12 July 2016

Turtles migrating north

For many, the song of the Turtle Dove is synonymous with warm summer days in our countryside. Thetford Forest, Norfolk has traditionally been a great place to hear them purring; however over recent years it has become increasingly more difficult to find them. The 2015 Breeding Bird Survey (BBS) report, published recently, puts the decline into perspective "Turtle Dove down by 93% in the UK from 1995 to 2014!". The full BBS report highlights other declines, but also some big increases.

The decline in Turtle Dove is also noted in the ringing totals, with an average of c. 40 birds ringed in the whole country since 2010 (and only 12 in 2015) compared to an average of almost 140 in the 1980s. With so few birds ringed, the re-encounter rate of a Turtle Dove is very low, but however slim, there is always a chance to provide useful data.

Colour of location: Ringed in Britain & Ireland, Found HereRinged Here, Found in Britain & Ireland
The majority of the recoveries of Turtle Dove have been in Portugal, Spain and France with just four sub-Saharan records. Soon the map above will need to be updated to show the 2016 records of a BTO-ringed Turtle Dove being found on the Faeroes! This second year Turtle Dove (below) was ringed on 23 May 2016 on Fair Isle only to be seen alive and the ring read on 30 June 2016 at Vidarlundin Park, Torshavn.

Turtle Dove on Fair Isle about to make another epic journey North. Photo taken by Lee Gregory.
Not only is this an exciting report for Fair Isle (the only other previous recoveries of this species were of a bird caught on 5th May 1982, which was shot in Spain on 01 September 1982, and another ringed on 6th June 1974, which was shot in France on 4th September 1977) but it is also a great report for the whole of Britain & Ireland. It is great to hear that this bird wasn't shot or found dead either.

Thanks to David Parnaby and the rest of the Fair Isle Bird observatory team for highlighting this.

07 June 2016

Two broods are better than one

Hazel Evans, NRS secretary writes:

Studies in Europe demonstrate that Great Tits have the potential to produce two broods per season; a recent study of populations in The Netherlands showed that over 50% of birds were double-brooded in the 1960s, though this number has been declining as the climate warms. Despite this observation, records of double-brooded Great Tits are still relatively scarce in the UK – is this because it is truly a rare behaviour or because we’re so used to thinking of them as single-brooded that we don’t often check our boxes after the first chicks have left?

Robin and Moya Myerscough from Norfolk have been keeping a very detailed log of the comings and goings at their garden in nest box during 2016. A female Great Tit began laying on 6th April and completed a clutch of nine, which hatched on the 27th. Unfortunately two chicks died but the remaining seven fledged successfully at 08.15 on 17th May.

Female Great Tit collecting nesting material. Photo taken by Jill Packenham

These observations constitute a great record for the BTO’s Nest Record Scheme but nothing seemed particularly out of the ordinary. However, by 2 pm an adult was bringing in fresh nesting material and it laid the first egg of a second clutch the very next day.  This in itself is unusual, but a gap of less than 24 hours between attempts seems amazing. Great Tit fledglings are heavily dependent on their parents for about a week after leaving the nest but it is possible the female was able to juggle these responsibilities with laying of the second clutch, given incubation does not commence until the penultimate egg is laid.

Great Tit removing a fecal sac. Photo taken by David Waistell

In truth, while it seems rapid, we don’t really know just how this observation compares to the typical interval between broods, but the widespread use of nest box cameras has the potential to significantly increase the amount of information we are able to collect. Whether you own a camera or not, it’s worth keeping a close eye on your nest boxes over the next couple of weeks to check for second broods – remember to submit records of any attempts you find  to  the Nest Record Scheme or Nest Box Challenge.