Tuesday, 10 September 2013

It's all over now... or is it?

I thought of this headline before Pete did his. (Great minds think alike - ed.) Ruth, Emma and meself went back to several Barn Owl boxes over the weekend (where birds had been present, on eggs etc back in the summer) to see what they were up to. Until then, only a paltry 12 chicks had been ringed on my rings, but by Sunday we'd added another 18! Surprisingly, this included broods of 4 & 7 in boxes c1km apart on the Smite, and the females had swapped boxes since last year. Makes you wonder if there's an alpha male providing for both of them. It was the first time I'd seen a brood of 7 and there are only 3 records ever of broods of 8 fledging. Chicks we have ringed have mostly been in clusters at Barkestone, Halam, Flintham, Normanton & Shelton, for reasons I'm not sure why.

Though the factors affecting the Barn Owls probably include:
  • 2012 started off as a promising short-tailed vole year, but the wet and cold summer/autumn hit them hard and very few were found cached.
  • Barn owls bred well to start with in 2012, but the poor weather and food availability hit them hard with lots of chick stage failures. Some boxes had the same female fail twice and in others two different females failed, and chick weights were low.
  • The poor weather continued into the autumn & winter/spring which caused very poor first winter survival. To maybe show this, in 2012 I processed 19 first summer barn owls, this year it was 5. In 2011 & 2012, I ringed c80 pulli. Not hellishly scientific, but a crude measure showing a 75% drop in first winter survival between 2011-12 and 2012-13.
  • The winter extended well into spring this year. The BTO had 3-4 times the usual recovery rate of dead Barn Owls and these, unusually, were mainly experienced adults who, for lack of food, left their territories and got killed on the roadside. In a good year they would have been on eggs by April.
  • Birds that survived to breed in 2013, either tried early on and mostly failed or appear to have delayed and are having some success now.
These late breeders, and I potentially still have 2 broods to ring in October, will need a good autumn to fledge this weekend's young and for them to find their feet.

Sorry if this sounds pessimistic! A mild winter (please) and a good vole year will allow the Barn Owls to come back from this very poor year for them.

Jim

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