The 2010 forecast for Barn Owl

by

Colin Shawyer
BTO BOMP – Wildlife Conservation Partnership
BOCN Co-ordinator UK & Ireland

For those of us involved in Barn Owl research and conservation, another season is upon us. This is the 22nd year of the Barn Owl Conservation Network (BOCN), two decades during which county and regional Advisors and their teams in partnership with landowners, farmers and other countrymen have played, and continue to play, a major role in the recovery of Barn Owls in Britain.

A pair of Barn Owls with eggs

The increase in local and regional breeding populations and the improved accessibility to nests through the use of special nestbox designs has, since 2000, enabled us to monitor a significant proportion of the UK population. The annual monitoring work which is coordinated through the BTO’s Barn Owl Monitoring Programme (BOMP), is now in its tenth year.

As most of you know I conduct a few early visits to nests in late March or early April in order to help those of you who monitor your sites a means of timing visits to record clutch size (if desired for registered BOMP sites) and brood size and avoid the most sensitive period of the breeding season just prior to egg-laying and during egg-laying.

This year I visited a sample of 11 sites on 12th April. Pairs were present at 7 sites and at 4 of these single eggs were present, indicating a first egg date of between 9th and 12th April.  The weights of females at the other four sites were below their breeding weight of 360g which indicates that they will not be in sufficient condition to begin laying until the end of April/early May.

Because of the synchronicity of egg-laying in British Barn Owls I think we can expect full clutches for about 35% of breeding pairs in Britain in the last week of April, suggesting that ideally nest visits to determine full clutch size (if desired for registered BOMP sites) should be undertaken during the second week of May. Although the window of opportunity is much wider for the second visit to record brood size and ring chicks, ideally this should be undertaken in the first and second weeks of July when chicks are about six weeks old at which age survival remains high and when brood size is usually synonymous with fledging success. For the other 65% of pairs which have yet to lay eggs, visits would be best conducted three weeks later than indicated above.

Clearly as always there will be exceptions to the norm, one pair in Cornwall that I know of, laid their first egg on Easter Sunday, the 4th April.

In overall terms the high vole year and good breeding season for Barn Owls I have been predicting for 2010 may be somewhat tempered by the severe winter and cold weather which we are still experiencing. However, the early egg-laying date (2-3 weeks earlier than normal) in what would appear, a significant proportion of Barn Owls, is indicative of a higher than average overall fledging success this year.  Nevertheless, breeding occupancy (ie. number of pairs present at traditional sites) may be lower than in the last two years, due to a higher than average mortality in juvenile and adult birds that has been reported to me during the prolonged snows this winter.

I would be interested to hear of any of your early observations, email: colinshawyer@aol.com

13th April 2010

The Barn Owl is specially protected under Schedule 1 of the Wildlife and Countryside Act,  making it unlawful to intentionally or recklessly disturb it whilst it is preparing to nest or is at the nest with eggs or young, or to disturb its dependent young. 

Inspection of nest sites can only be undertaken by experienced fieldworkers holding a licence issued by the appropriate countryside agency:  Countryside Council for Wales, Natural England, Northern Ireland Environment Agency, Scottish Natural Heritage.

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