11 October 2010

Never too late!

The Barn Owl has become one of the most intensively monitored species in the UK. In late summer breeding season would normally be over but this year was a bit unusual as Colin Shawyer recollects...

"In May and early June almost a third of pairs had not attempted to lay and they were unlikely to do so later in the year (due to very low body weights). In mid July gales that lasted three days and nights, prevented adults from hunting and caused entire broods to starve, many of which were only two weeks from fledging.

So far so bleak. But returning to that third of pairs that were on territory but not laying: an interesting observation was noted. At some of those sites the adult females—and even some males—had begun their wing moult, which is a good indication that a pair has ‘given up’ for the season and is unlikely to breed. But at a greater proportion of those nest sites no such moulting was seen. How important these observations turned out to be!

My colleagues and I decided to re-visit many sites in late August and early September and found healthy broods of fours, fives and sixes. The ages of many of these chicks indicated that the eggs had been laid in late June after our earlier visits, when we had weighed the females and surmised they were not to breed. Even some traditionally-used nest sites that were vacant in June contained large and healthy broods.

Had we stuck to our usual plan of only revisiting sites in August where breeding had already been noted, we would have missed a surge of late first-nesting attempts. So it goes to show that there are never two breeding seasons the same for a nest recorder! Overall breeding success in 2010 will not be as quite as bad as we had originally feared."

By Colin Shawyer
BTO - BOMP-Project Development and Monitoring
BOCN - Project Director, UK and Ireland

Follow Colin Shawyer's thoughts on Barn Owl monitoring in his blog or get involved in the Nest Record Scheme next year!

No comments:

Post a Comment