28 October 2014

Bumper Barn Owl breeding season

Barn Owls are one of our most iconic and recognisable birds. Over the past couple of years this species has struggled due to severe weather events, with last year being particularly difficult as reported here and here. It is estimated by Colin Shawyer of the Barn Owl Conservation Network (BOCN) that only one third of the British Barn Owl population attempted to breed in 2013.

Successful Barn Owl breeding seasons are dependent both on favourable weather conditions and food availability. The primary food item for Barn Owls is the Field Vole which demonstrates cyclical population trends. Reports coming in to us here at the BTO suggest that 2014 is a good vole year and as a result, may turn out to be the best Barn Owl breeding season since 2007. Early estimates from the BOCN suggest that an average of 33% of pairs have had second broods this year, although in some areas, this figure could be as high as 65%. Average brood size (first and second broods) is also high although the recent spell of wet and colder weather may have impacted on fledging success for some broods.

Whilst we have not yet had all of the ringing data for 2014, the totals are already up on last year. For example, in 2013, only 20 Barn Owls were ringed in May and 183 were ringed in June. This year to date, we have received the details of 428 Barn Owls ringed in May and 1,814 ringed in June!

Adult Barn Owl (photograph by Ruth Walker)

The following stories have been sent to us by some of our Barn Owl ringers and nest recorders:

Chris Griffiths of the Montgomeryshire Barn Owl Groups writes:

Our record year was in 2005 when we had 73 pairs producing 249 pulli. Following the two hard winters of 2010 and 2011, then deep snow in March 2013, we slumped last year to 14 breeding pairs producing 49 pulli. This year Montgomeryshire had 37 pairs producing 149 pulli. Interestingly a third of this year’s birds have been recorded at “new sites”, either newly erected boxes, or boxes that have been up a while but have never been used. Many of the “traditional” sites remain empty. For the first time since I have been involved with MBOG, thanks to ringing, I can confirm that we have also had a few second broods this year.

One unusual instance this season was that I found a ringed female bird in a box with four young on 12/6/14. This female was ringed by me in 2013 and counting back she must have started breeding at eight months of age.  On 21/7/14 I found her again 4.4 km away on a second brood of six eggs and one freshly hatched chick. A quick chat with Colin Shawyer revealed she must have left her first brood nine days after I had ringed that clutch. Apparently, this is not unusual but the distance of 4.4 km is! She almost certainly took up with another male, probably on the edge of his “territory” and left the first male to bring up the kids alone (this is something BOCN were beginning to suspect at a number of sites in years where double brooding occurs).  The good news is that the first brood of four and the second brood (which had dwindled to five when I ringed them) all fledged successfully. On returning to the first site at the end of August, we found “superdad” (who was caught and ringed in a nearby box earlier in the season) in the box with another male that I had ringed as a pulli last year 11 km away.

Barn Owl chick (photograph by Ruth Walker)

Alan Ball writes:

Barn Owls have done exceptionally well in Lincolnshire this year. Bob Sheppard and I have monitored nearly 400 nesting attempts from at least 340 pairs and have ringed over 1,200 chicks. We have not rechecked every site, so will have missed many second broods as probably around a third will have attempted to breed again. Now, in mid-October, some of the late second broods are struggling as weather and food availability has an effect, but we are still finding a few healthy broods. Of particular note this year was one fen just south of Bourne, which had six pairs, raising four broods of seven and two of five. It's amazing that one fen of approximately eight square kilometres could furnish enough food for 12 adults and 38 young. Prey encountered in nest-boxes suggests that there has been an abundance of field mice as well as voles this year.

As well as Barn Owls, other species have taken advantage of the abundance of prey and Bob and I have also ringed 449 Kestrel chicks out of 150 pairs monitored, 188 Little Owl chicks from 80 pairs and 120 Tawny Owl chicks. I am now part-way through the daunting task of completing all the Nest Record Cards to record the 2,500 birds of prey handled this year.

Peter Wilkinson sent us this wonderful photograph (taken by Chris Chatfield) of five Barn Owl chicks sitting on their box. 

Geoff & Jean Sheppard, who carry out a RAS project on Barn Owls, write:

Our study area is in the SW corner of Scotland where we monitor about 80 sites, the majority of which have a nest box. Although there was not a large increase in occupied sites, few had single birds and most were successful with notably larger brood sizes. The number of pulli ringed almost doubled but the number is still well below the usual 150+ achieved in the previous decade. For the first time in many years, a pair at one site had two broods, a six and a four. Interestingly, in certain areas, many sites remained unoccupied suggesting that vole numbers had not increased uniformly and this may be due to the fragmented habitat in the study area. This year, in three occupied sites the pulli failed to survive due to death of one or both adults. In one case, this was due to Jackdaws completely blocking the nest box entrance and trapping the female with her chicks at the back. On a lighter note, a pair in a derelict cottage forsook their usual loft space and raised their brood on the corner of an old bunk bed!

Colin Shawyer writes:

Perhaps my most well studied Species Recovery Areas is that in the Peterborough District. This work was initiated in the early 1990s and, as a result of concerted conservation effort, has seen an increase in the breeding population from six breeding pairs in 1992 to 60 pairs today. The 80 artificial nest sites which have been installed here, largely on a 1.5 km grid matrix, have been monitored annually during the last 20 years and the study area now represents the highest density of breeding barn owls in the UK. This year has seen 75 of the potential sites available in the study area, occupied by 60 breeding pairs with about 70% of these double brooding. The average first brood size (close to fledging) this year is slightly greater than four with ringed broods of six, seven and occasionally eight at about 50% of sites. Second broods are still being ringed but as is normally the case, although clutch sizes are generally higher than in firsts, brood depletion is almost always greater with some having gone from seven chicks to fledge one, two and three. The average second brood size at ringing is, nevertheless likely to remain above three. At a few sites, fledging success over both broods has exceeded ten!

16 October 2014

Tay Bearded Tits on the move: can you help?

In the UK, the largest single population of Bearded Tits, also sometimes known as Bearded Reedlings, occupy the Tay reedbeds, in eastern Scotland. Over the 2014 breeding season, Tay Ringing Group have been working hard to monitor this important population, ringing an incredible 635 birds - and now these birds are on the move...

The Tay reedbed runs for 15km along the estuary, the largest continuous reedbed in the UK

Around this time last year, Iain Malzer conducted a radio-tracking study of these elusive birds, following them around the reedbed. He was intrigued when he found that none of them moved out of the Tay area during what is assumed to be a traditionally dispersive period. However, this year the picture is quite different. When the population reaches the huge numbers we’ve seen on the Tay this year, ‘Beardies’ sometimes undergo irruptive movements, flying in small flocks in all directions. By understanding the extent and drivers of these movements, we can observe how connected these birds are at a population level, how they remain stable genetically and how they colonise and occupy new areas of reedbed.

Photo (c) Amy Lewis
Typically though, this year Iain didn’t have any trackers on the birds, and so is now asking for help in finding these dispersing birds. As previous Demog Blog posts have suggested, the birds can turn up in the smallest patches of reed, so we are checking everywhere for sightings of colour-ringed birds. Already we’ve had reports from the Isle of May, Aberdeenshire and Loch Leven, but birds can move much further: the longest recovery within the UK was a 390km movement between Suffolk and Devon, and other records have even shown birds moving abroad. This is our chance to record the first long-distance movements from the Tay population.

Many of the birds ringed on the Tay have unique colour-ring combinations, allowing us to identify exactly who they are. Birds may have three colour-rings in any combination of red, orange, green, yellow, light blue, dark blue, white, grey and black. Reports of any sightings, colour-ringed or not, at your local reedbed will be an essential contribution to the understanding of the movement systems of these peculiar birds and their wider conservation.

One of the colour-ringed birds (a female) from the Tay reedbed
To report a sighting drop Iain an email or get in touch with us here at Demog Blog.

So if you're out over the autumn and winter, listen out for the unique ‘pinging’ of Beardies (have a listen on xeno-canto here) and let’s leave no reedbed unchecked.

14 October 2014

Technical wizardry helps monitor Merlins

For many of us who can’t enjoy this species on its breeding grounds in the moorlands and uplands, the Merlin (Falco columbarius) is a bird of autumn and winter when they can be spotted in the lower lands chasing Skylarks or other passerines. The BirdTrack graph below illustrates that pattern, with an obvious peak in October. An increase in sightings in October is potentially also due to the presence of passage migrants and the incoming winter population.

Merlin chart from BirdTrack
Recently, Roy Filleul, a birdwatcher and photographer from Jersey, captured images of a juvenile Merlin on the side of a pond. The following day we received a phone call from a member of the public reporting a Merlin that had been taken into care in the JSPCA (Jersey Society for Prevention of Cruelty to Animals). Unfortunately this was the same bird that had been photographed by Roy and, sadly, it didn’t survive due to injuries.

Merlin, by Roy Filleul
The bird in question was ringed in the nest last June in Lancashire, one of their strongholds (click here for top five counties for species in 2013). Although this Merlin didn’t travel a long distance or move in an unexpected direction, this is the first time one ringed in the UK has been found in the Channel Islands.

As you can see from the photograph, as well as being ringed, this bird was also PIT (Passive Integrated Transponder) tagged. These tags work in a similar way to Microchips for a dog or cat except that they are mounted externally (on a ring) rather than being inserted under the skin and are read by a receiver placed by the nest (by a licence holder). Metal ringing allows us to gather information on movements as well as survival; for example, it is possible to infer that when you stop catching a bird, that is normally caught year on year at a particular site, it has not survived (the principle behind the Retrapping Adults for Survival Scheme). As it is often very difficult to re-catch adult raptors, using a PIT tag allows us to follow a bird throughout its life to obtain data that categorically tells us the bird is still alive. If nests are monitored by a licensed nest recorder, levels of productivity over its lifetime can also be obtained from PIT tags. Unfortunately, as this bird died before returning to its breeding grounds, we will never know what information we might have gathered from this individual.

Currently in the online ringing database we have 54 recoveries of UK-ringed Merlins that have been found abroad, 35 of them in France. Also notable are the 31 Icelandic Merlins found in the British Isles, mostly recovered in Ireland. This reflects the fact that many British breeders winter on the continent and our remaining winter population is joined by winter visitors, predominantly from the Icelandic breeding population. See map of recoveries below.

Merlin recoveries map, from the online reports

07 October 2014

Looking out for Twite

As a breeding bird, Twite Linaria flavirostris has undergone a 19% range contraction in Britain since the 1968-72 Breeding Atlas (Balmer et al 2013). The stronghold for breeding Twite in England is the southern Pennines where the population has undergone declines possibly due to reduced availability of seed later in the breeding season (restricting second broods), reduced availability of suitable nesting habitat and moorland fires (RSPB England Twite Recovery Project). 

Steve Christmas and Jamie Dunning started a new project to monitor this population in 2014 and are seeking help looking for colour ring re-sightings. Birds will be on their breeding grounds between April and September but previous monitoring projects and information from ring recoveries suggest that the birds from the Pennines population winter (October to March) on the North Sea coasts between the Wash and the Thames (Wernham et al 2002). In total, there have been six UK based Twite colour ringing projects registered with the European colour-ring birding website although not all of these are still operating. Details of the colour ring combinations used for this project are described by Jamie below.

Jamie Dunning writes:

The South Pennines are the last bastion for resident breeding Twite (Linaria flavirostris) in England and are therefore home to a very important population of these birds (which belong to the endemic ssp. pipilans). Following on from historic research done by Andy Brown, David Sowter, AndrĂ© Raine, Sean Gray et al, Steve Christmas and I have started a colour ringing project on this species this year. As with the previous research, we will monitor movements as well as population dynamics and productivity over the coming years.

Female Twite. Photograph by Edmund Fellowes.
As with all colour ringing projects, publicity is key to getting data back in the form of re-sightings! The Twite we are ringing in the Pennines are being fitted with plain colour rings. We are fitting a single colour ring on the left leg over the standard BTO metal ring and two colour rings on the right leg. The colours used in our project are as follows:

Black (N)
White (W)
Pale Blue (P)
Blue (B)
Green (G)
Orange (O)
Yellow (Y)
Red (R)
Metal (M)

We have ringed approximately 100 birds in 2014 so far. Any birds seen with a combination of the above should be reported to Steve Christmas at: se.christmas@ntlworld.com or myself at: jamiedunning8@googlemail.com. Either of us would be more than happy to give any further information or answer any questions you may have. We would be very grateful if any sightings of birds that are not part of our project could be reported to the appropriate research group (www.cr-birding.org). [As well as replying to you they will inform their ringing scheme of the sighting, adding to the knowledge of this species' movements.] - Eds

For further information on Twite in the South Pennines see the RSPB’s project pages on what they are doing in the way of conserving upland habitat for birds.

Thanks for reading!

Balmer, D.E., Gillings, S., Caffrey, B.J., Swann, R.L., Downie, I.S. & Fuller, R.J. (2013) Bird Atlas 2007-11: the breeding and wintering birds of Britain & Ireland. BTO Books, Thetford.
Wernham, C.V., Toms, M.P., Marchant, J.H., Clark, J.A., Siriwardena, G.M. & Baillie, S.R. (eds) (2002) The Migration Atlas: Movements of the birds of Britain and Ireland. T. & A.D. Poyser, London.