Saturday, 18 November 2006

A bad year for owls

It appears that 2006 has not been a very good year for our breeding owls. The latest information to have been published by the British Trust for Ornithology’s (BTO) Nest Record Scheme, suggests that many tawny owl nest sites were unoccupied this year. Tawny owls start nesting early in the year, with breeding territories established during the first part of the winter (which is why you may hear them calling now). A combination of food availability and weather conditions will determine if they then go on to breed. It appears that last winter there was simply not enough small mammal food around for many pairs to get into breeding condition and so they gave it a miss.

Barn owls, of which Norfolk holds a sizeable population, fared slightly better, with occupancy rates at monitored sites only down by a small amount. However, high levels of chick mortality and small brood sizes at fledging suggest that even these enigmatic birds were struggling to find sufficient food for their growing chicks. Even so, our barn owls fared somewhat better than those in the southwest of the country, where very few pairs managed to rear their broods of downy youngsters.

Such short-term failures in themselves are not necessarily going to have a long-term impact on the owl population, especially for a species like the barn owl which has tremendous reproductive potential. If 2007 proves to be a good year, with abundant food and good weather, then they should make up their losses. It is for this reason then, that the BTO monitors breeding success each year, extracting long-term patterns which may signal that a species is in difficulty. If a species shows a significant long-term decline in breeding success over many years then the BTO can issue an alert, warning the Government’s conservation advisors that there is a problem. The Nest Record Scheme’s current alert list contains 21 different species. Included in these are familiar birds like kestrel, which has shown a significant decline in brood size (the number of chicks in the nest) since 1990. Also included are the barn owl and bullfinch; the latter has, since 1990, experienced increased levels of nests failing at the egg stage. Could this be due to predation?

While the reasons for the patterns seen in individual species may differ from one species to another, there may also be underlying causes linked, perhaps, to global climate change (we know that many species are nesting earlier now than they did 20 years ago) or to changes in the nature of our countryside. As such, it is essential that we continue to monitor breeding success and to identify those species that need conservation action.

No comments:

Post a Comment