9 October 2017

Mixed fortunes for Cornish Barn Owls in 2017

Just before we get carried away with ringing autumn migrants, it's a good time to have a look back at the 2017 Barn Owl season. With extra project funding coming in and new boxes located and/or erected it's been a busy summer!


2011 2012 2013 2014 2015 2016 2017
Sites visited 32 34 32 44 41 47 64
Unoccupied 2
(6%)
7
(21%)
12
(38%)
11
(27%)
11
(27%)
12
(26%)
23
(36%)
Occupied but no breeding 13
(41%)
2
(6%)
7
(22%)
7
(18%)
7
(12%)
8
(17%)
5
(8%)
Average clutch size
(where observed)
4.8 4.1 3.6 4.6 4.6 4.6 5.3
Average brood size
(where observed)
3.1 3.1 2.4 3.5 3.5 2.8 3.0
Number of chicks ringed 33 46 19 63 70 47 90

With so many new boxes put up in recent years (thanks to generous funding from Paradise Park), it's perhaps not surprising that the apparent occupancy rate was slightly down in 2017, but this will no doubt improve over time as birds move into some of the newer boxes. The relatively dry spring would have been quite good for rodent numbers, but it was still surprising to find so many large clutches, with an average of 5.3 being the highest we've seen since we started monitoring in 2011.

However, as the weather deteriorated into the summer, we weren't expecting quite such large clutches and this proved to be true, Most sites saw quite significant brood reduction, though the average brood size of 3.1 was still pretty good given the conditions. After the four complete failures in 2016, we only saw two this year which is more normal. We also some failures just after fledging, with two chicks from one brood found dead in surrounding fields soon after fledging, and two chicks from another found dead in a water trough a month after fledging.

But the total of 90 chicks ringed was also our highest to date and hopefully we'll break the 100 barrier next year. As far as adults go, we retrapped several adults, including one male that has now been in the same box since 2011. We also retrapped an adult originally ringed at a site in 2015 (where it raised three chicks), then found in a box just over a kilometre away in 2016 (didn't breed), but then back in it's original site for 2017, but still not breeding. It'll be interesting to see if it breeds next year, and if so where.

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