Abstract from BTO Research Report No 408:

Leech, D.I., Banks, A. & Crick, H.Q.P. (March 2005)

The Influence of the 2001 Foot and Mouth Disease Outbreak on Barn Owl Productivity in the UK.

Executive Summary

1. The Barn Owl is a scarce breeding species that underwent substantial decline in the UK during the 20th century. It is currently on the Birds of Conservation Concern Amber listing due in part to the fact that the species has declined in abundance by greater than 25% over the last 25 years, and it is subject both to a conservation action plan and to a number of local Biodiversity Action Plans.

2. In 2001, the UK was seriously affected by an outbreak of Foot and Mouth Disease (FMD), resulting in the slaughter of a significant proportion of the national herd. Large parts of the countryside were placed under access restrictions and rodenticide use increased.

3. Increased levels of activity around farms during the breeding season may have resulted in increased disturbance and reduced Barn Owl breeding performance. Increased rodenticide use could also have negatively impacted on survival rates of adults and offspring. Conversely, these potentially detrimental impacts might have been offset by reductions in disturbance following the imposition of access restrictions and the potential impact of reduced grazing pressure leading to improved grass swards and hence to larger prey populations.

4. Data concerning the location of Barn Owl breeding attempts, occupancy rates and breeding performance were collected by participants in the BTO Barn Owl Monitoring Program (BOMP), funded by The Sheepdrove Trust, from 2000 onwards. A significant amount of Barn Owl productivity data (currently 600+ records p.a.) is also collected annually by participants in the BTO Nest Record Scheme, funded by the BTO/JNCC partnership.

5. Data concerning the location of land to which access was restricted, premises at which livestock were slaughtered and premises at which FMD infection was confirmed were obtained from the Central Science Laboratory (CSL) FMD database. Data concerning rodenticide use at premises in a restricted set of counties, predominantly in the north of England, was obtained from a database held at the Rural Development Service

6. BOMP data, NRS data and the FMD datasets were mapped using the ArcView GIS mapping program. The program was then used to calculate the minimum distance between each individual Barn Owl record and the location of a farm at which access had been restricted, a farm where livestock had been slaughtered, a farm where FMD infection had been identified and a farm where rodenticides had been used.

7. The Barn Owl data were then split into two categories – records that were within 5km of farms at which FMD-related measures had taken place, and those that were greater than 5km from any such premises. The influence of FMD-related measures on occupancy and breeding performance were then analysed separately for pre-outbreak (1998-2000) and post-outbreak (2001-2003) datasets using a repeated measures GENMOD procedure in SAS, controlling for northings, eastings, year and habitat type.

8. In general the results suggested that any impacts of FMD-related measures on Barn Owl occupancy rates and breeding performance were likely to have been marginal. Although occupancy rates at the set of Core BOMP monitoring sites was lower near land with access restrictions after the FMD outbreak compared with sites further away a similar result was not found among the larger sample of BOMP Network Sites monitored by volunteers. Similarly occupancy rates were lower at BOMP Core sites near farms where slaughter had occurred than at those which were more distant, but the sample size was very small for the former category and the result was not repeated for BOMP Network Sites.

9. Interestingly, both occupancy at BOMP Network sites and clutch size at all sites was greater post-outbreak, but not pre-outbreak, near infected premises than at sites that were more distant. It is possible that slaughter and/or disinfection took place more rapidly at these sites, reducing disturbance. In addition, clutch size was larger near sites where rodenticides were used, than at sites more distant, perhaps suggesting that rodent populations were higher at these farms, hence the need for increased control. However, it should be noted that for these analyses the sample sizes of some of the categories were relatively small.

10. Overall, on the basis of these analyses there is relatively little evidence to suggest that the FMD operations had major impacts on the Barn Owl populations using the affected farms. The results tend to be contradictory and only relatively weakly significant between different aspects of the types of FMD treatment, suggesting that other confounding factors might be affecting the results. Care should be taken when interpreting some results, significant proportion of the Barn Owl records that are within 5km of infected farms and those at which slaughter occurred originate from a relatively limited geographical area.


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