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!


  1. Just a small correction - field vole populations are not really cyclical in Britain, especially in the lowlands where most Barn Owls are found (see the Handbook of Mammals of British Isles (Harris & Yalden). They're best thought of as 'unpredictable', with good and bad years following no real pattern, but probably related to autumn/winter weather and food, and predator density. A bad few years for Barn Owls means less predators for voles, so higher survival!

    1. Good point. There is a great deal of research still waiting to be carried out on barn owls, but this does not appear to be happening.