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.

27 May 2016

Elderly Shag strengthens our position in Europe!

Jim Lennon from the Shiants Auk Ringing Group writes:

Ringing seabirds can be mucky and challenging work, especially when you’re ducking under a rock to reach a Shag chick, while keeping an eye out for its protective parents (often the croaking male). However, this is soon forgotten when you receive news of one of them nearly 31 years later!

Shag chick 1227282 was one of a brood of three ringed on the Shiants Isles, Western Isles, on 30 June 1985 by Ms Sam Powell, a trainee ringer from South Wales working with the Shiants Auk Ringing Group. A total of 725 pulli from 377 broods was ringed on the Shiants that year.  Most of the subsequent recoveries were of birds that perished within the first 12 months, a few survived for four or five years and an exceptional bird was found dead after nine years.

But 1227282 outlived them all by a country mile.  For the next 30 years following ringing, it most likely spent its life breeding on the Shiants and in the waters of West Scotland, but we’ll never know for sure as it was never heard of again until John Taynton, a RSPB worker on the Shiants, found it freshly dead on 26 April 2016 i.e. a life span of 30 years 302 days.


According to the BTO’s latest longevity list (2014), this makes the Shiants bird the oldest ringed Shag in Britain & Ireland, and also in Europe (see Euring), raising the record by nearly a year.

The Euring information is not updated as regularly as the BTOs longevity lists because it needs to access all the data from all the Euring ringing schemes and this can take some time.  It currently indicates that a 34 yr old bird from the Shiants is Europe's oldest  Puffin but two just shy of 36 years old and one almost 37 years old, are listed on the BTO longevity records site.

16 May 2016

RAS: Renewing Acquaintances in Spring

For almost 20 years, the Retrapping Adults for Survival (RAS) scheme has used standardised bird ringing as a tool to monitor adult survival rates of species not frequently caught at Constant Effort Sites. The results are used to generate annual survival estimates which help us to understand more about the contribution changes in the probability of mortality make to population trends recorded by surveys such as the BTO/JNCC/RSPB Breeding Bird Survey (BBS). Birds are generally faithful to breeding sites between years, so RAS methodology aims to re-encounter as high a proportion of returning adults as possible each year; for some species, this task can be made significantly easier by fitting colour-marks, allowing birds to be individually identified without capture. 

The initial uptake for RAS was fantastic, with 75 datasets received in 1998. Since then, the number of projects has risen steadily and in 2015, a tremendous 190 datasets were received. We now have over 200 active projects studying 59 different species. 60% of projects focus on one of the 24 target species, as outlined in the Demographic Targeting Strategy, with a further 11% of projects targeting seabirds (which don’t yet feature in the target species list).

The most frequently studied species are still House Sparrow and Pied Flycatcher, which are the focus of 23 projects each. In third place is Sand Martin, which is studied by 15 RAS ringers, often at artificial banks such as the one at Rutland Water which enable breeding success to be monitored concurrently. Following closely behind is Starling (14 projects), a species that has become increasingly popular in recent years. Prior to 2013, there were only two RAS projects on this red-listed species so the additional data now being produced are very welcome! Not quite making double figures are Dipper and Reed Warbler, which are the species of choice for nine RAS ringers each. Perhaps surprisingly, there are still fewer RAS projects than we might expect on some generally well-ringed species, such as Swallow and Tree Sparrow (six projects each) – we would love to hear from anyone interested in taking up the challenge of a RAS on these species.

This colour-ringed Starling is part of a RAS population in Lancashire. Photo by Peter Alker.

The fruits of RAS ringers’ labours have just been published. The full suite of national RAS results for 2015 is now available and includes a trend for Tawny Owl, which we have been able to produce for the first time following the submission of some valuable historical data. RAS works particularly well for longer-lived species, such as owls and seabirds. A number of ringers with existing, long-term ringing projects have recently registered for RAS, instantly enabling us to produce survival trends for their studies.

A trend for Tawny Owl is available for the first time. Photo by Ruth Walker.
RAS survival trends for 12 species (Little Owl, Jackdaw, Sand Martin, Swallow, House Martin, Dipper, Pied Flycatcher, Stonechat, Wheatear, House Sparrow, Linnet and Siskin) are also included in the annually produced BirdTrends report, which provides a range of information about population trends and their potential drivers for over 100 breeding bird species.

We are very grateful to all our fabulous RAS ringers who put so much time and effort into generating this incredibly valuable data. Anybody considering starting a RAS or wondering whether a current project could be suitable for RAS is encouraged to contact the RAS organiser.