A dark-breasted Barn Owl

I received a report last week of an unusual visitor to the county, in the form of a dark-breasted Barn Owl. While our ‘white-breasted’ Barn Owls will be familiar to most readers (Norfolk being a particularly good county for them), birds of the dark-breasted race remain very occasional visitors from Continental Europe. More correctly known as ‘guttata’, this dark-breasted race breeds from Germany, eastwards to the Ukraine and Bulgaria. Populations to the west of this range are ‘white-breasted, belonging to the race ‘alba’. Birds of the dark form tend to be more heavily marked, with more spotting on the breast and around the facial disk. In addition, they show a soft warm ochre wash across the breast which gives them their name.

One of the reasons why we don’t receive more such visitors is because Barn Owls are rather sedentary birds, their young rarely dispersing far from the nest. An analysis that I carried out of ringing data for the BTO’s Migration Atlas revealed that the average distance moved by young Barn Owls here in Britain was just 12km. These youngsters dispersed away from the nest over a four or five month period and after this made little additional movement. The relatively sedentary nature of our Barn Owls contrasts with what is seen on the Continent, where youngsters can move considerable distances. Interestingly, the average distance moved by these Continental birds has been shown to vary from year-to-year. In some years there is a pronounced degree of dispersal, with the young on the move from late summer and not settled until November. Such years have been given the name ‘Wanderjahren’ and are thought to result from the combination of a particularly successful breeding season followed by a sudden crash in the vole population ­– voles are the main prey species and their numbers vary in relation to the availability of softer grasses and herbs.

There have been some rather dark-looking Barn Owls caught at breeding sites here in the East of England over the years and some of these birds may well have been mixed race birds. However, proving this can be difficult because the different races are well-represented in collectors aviaries and some of these do escape or are deliberately (and illegally) released. That dark-breasted individuals do reach our shores has been proved thanks to bird ringing, with a handful of ringed youngsters from Continental populations found here over the years. This most recent report also involved a ringed bird, this time coming from the Dutch population. In this respect it is similar to a Dutch-ringed individual found dead in North Norfolk back in October 1999 by Mike Crewe. This bird was stuffed and mounted and sits watching over me as I type these words.