Colin Shawyer's Barn Owl update July 2014

Widely recognised for his work on the study and conservation of owls and raptors, professional ecologist Colin Shawyer has collaborated with the BTO on projects such as Project Barn Owl (1995-1997) and the Barn Owl Monitoring Programme (2000-2009). As founder and co-ordinator of the Barn Owl Conservation Network (BOCN), Colin is in regular contact with Barn Owl experts across the country and oversees the annual monitoring of over 3,000 Barn Owl nest sites.

Value of conservation and research

In the 25 years since founding the BOCN I have installed and contributed 3,500 artificial nest sites. These, together with boxes provided by my BOCN colleagues have played a big part in the recovery in Barn Owl numbers since the last population estimate in 1997. In addition to their benefit for conservation, regular monitoring of these boxes has provided data for BTO surveys such as

in the mid-1990s, the Barn Owl Monitoring Programme in the 2000s, and the recent BTO Atlas, as well as supplying BOCN with the mid-season information necessary for providing updates such as these.

Better breeding in 2014

As predicted in my earlier forecast for the Barn Owl breeding season in 2014, this is proving to be an exceptionally good year and may well end up being more productive for the birds than the high of 2007.  Back in the 1980s, using BTO annual ringing data, I was able to show that the cyclic frequency of Barn Owl breeding productivity is 3.4 years, so it perhaps unsurprising that seven years on from that last high we are once again at the peak of this apparent cycle.

Early start for many pairs

Out of the 1000 nests I've monitored so far this season, in counties from Yorkshire to Sussex, about two-thirds of pairs began laying between the last week of March and first week of April, which is the earliest average laying date I have recorded since BOCN's inception in 1988. Across English and lowland Scottish counties, pairs have been highly synchronous, although in some parts of Wales things have been less predictable. Of the remaining third of pairs, some laid during the last few days of April—the 'typical' time—and a few exceptionally early birds in late February/early March.

The sizes of first broods is currently averaging more than four, which is very rare for the UK, and clutches of seven and eight, and near-fledged broods of six or more are proving not uncommon this year.

Some females already on second broods

Of those early pairs whose young are now close to fledging, at 50-60 days old, some females have already started or even finished second clutches, leaving the males with the overlapping task of feeding first brood juveniles for another two weeks and incubating females for another six. Although this means an even greater reliance on vole numbers remaining high, from the looks of prey larders in boxes, males appear to be coping well at the moment.  Most of these second clutches have been laid in nearby boxes, but some females have been found sitting on eggs alongside their first broods.

Second clutches are also on the cards for pairs that laid eggs before about 21 April, indeed eggs have already been laid at some of these sites and others are likely in mid to late July. This is reinforced by the fact that I have found little sign of female wing moult at the hundreds of sites I have visited. Suspension of wing moult during first clutches is a good indicator that females have the ability to lay again.

Box occupancy down at some sites

Occupancy levels at traditionally-used boxes are about 10-20% down this year in most of the counties I have visited. Conversely, and perhaps surprisingly, however, a significant number of newly installed boxes and older unoccupied sites have been used this year for the first time. Moreover, a high proportion of breeding females (and probably also males) captured at both traditional and newly occupied nests have been first-year birds.

If these observations are confirmed by other Barn Owl recorders, this would suggest both that adult mortality was, as we expected, especially high in 2013 following the adverse weather in February and March that year but that, despite a poor breeding season, those juveniles that fledged coped well over the mild winter just gone, no doubt aided by the very high vole abundance. That said, there have been many cases where adult birds found missing and feared dead in 2013, are now back at their traditional nest sites this year.

Unusual sightings

A few instances of breeding Tyto a. guttata may also arise this year in parts of England; a female I captured with young last week in Yorkshire might be one of these.  Despite my experience of T a. g in eastern France, I have yet to decide between this race or perhaps an especially dark T a. a!

What for the rest of 2014 then?  It looks as if we will need to be monitoring our Barn Owl sites into late Autumn given the likelihood of second broods. I'm not sure who will run out of steam first—us or the owls!

STOP PRESS:  Five year old ringed female weighing 410 g on 11 fresh eggs and still laying (thought to be a second clutch) found in one of my boxes in Norfolk yesterday.

Colin Shawyer

1 July 2014

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