Factors influencing diet, reproductive success and road mortality in the
      Barn Owl (Tyto Alba)
Creators: name: Wright, Rebecca
Publisher: name: Lancaster University
Year: 2019
Subjects: Barn Owl
Diet
Road Mortality
Reproductive Success
Habitat

description: In the UK, a decline in the Barn Owl population has been attributed to
      increased agricultural intensity and urbanization. Shifts in farming
      practices have resulted in a reduction of habitat diversity and
      homogenization of the UK's landscape, causing a reduction in the
      number and diversity of prey animals for predatory species. One species
      that has been affected by these ecological shifts is the Barn Owl. The
      expansion of road networks, to accommodate more vehicles on the road, has
      led to habitat fragmentation and ecological traps. The Barn Owl has
      shifted its feeding patterns due to the pressure of ecological traps
      caused by the expansion of road networks to accommodate more vehicles and
      are now the most frequent bird species encountered on road casualty
      surveys, with over half of known Barn Owl deaths being a result of
      wildlife-vehicle collisions. The objectives of this study were to
      investigate factors affecting diet and reproductive success in the Barn
      Owl, as well as to identify characteristics of Barn Owl road casualty
      hotspots.
      
      The study was conducted in Anglesey, north Wales. Diet was investigated
      through the morphological analysis of owl pellets; 377 pellets were
      collected from 26 nest/roost box locations during the Barn Owl breeding
      season and winter roosting season. Reproductive success was analyzed using
      data provided by the British Trust for Ornithology (BTO), and nest/roost
      box locations allowed habitat analysis to be performed using Arcmap GIS.
      Barn Owl road mortality hotspots were investigated using data provided
      from the North and Mid Trunk Road Agency in correspondence to Arcmap GIS
      and Google Earth, which allowed for habitat analysis. The date that the
      road mortality was reported to the North and Mid Trunk Road Agency was
      used for the seasonal analysis. Data provided by the BTO allowed the
      effects of population in relation to road casualties to be studied, using
      reproductive success as a proxy for population success.
      
      The results of the study found, 12 species of vertebrates form
      regurgitated Barn Owl pellets, with the three most abundant being the
      Field Vole (60.52%), Common Shrew (16.31%) and Wood Mouse (8.65%). The
      results of the study found that the mean field vole weight per pellet was
      higher outside the Barn Owl breeding season (64.65g) than during it
      (53.53g). The mean Wood Mouse weight per pellet was lower outside the
      breeding season (4.06g) when compared to inside (7.16g). The home range of
      the Barn Owl is typically within the 1km-4km radius around the nest site,
      which is compromised of a variety of habitats depending on location. The
      Barn Owl home range habitat composition on Anglesey varied from 14-99%
      agriculturally improved grassland, 0-43% arable horticulture and 0-9% fen
      marsh swamp. These habitats were found to have a negative association with
      the number of successful fledglings per nest, which could reflect prey
      availability and abundance within these habitats, as an owl which can
      provide more food will be able to raise more young. However, small mammal
      trapping would be needed to confirm the abundance and availability of prey
      in these habitats. There were 117 Barn Owl road casualties on the A55
      Anglesey recorded by the North Trunk Road Agent between 2001 and 2017,
      this equates to 0.196 Barn Owls/year/km. The month of April incurred the
      most deaths (18) and the least August, with only 1 death being reported.
      No relationship was identified between the time of year and the number of
      Barn Owl road casualties. Additionally, no relationship was found between
      habitat and owl road mortalities. However, a relationship was found
      between the presence of grass slope verges at the side of the A55 and
      bi-monthly road mortality. For instance, the number of deaths of barn owls
      in areas with grass sloping verges were reported as 29 and those without
      grass slopes recorded as 87.
      
      In conclusion, the results from this study highlights that in areas of
      intense agriculture, maintaining species rich diverse habitats is
      important for the success of Barn Owls. The results of this study suggest
      conservation efforts should be focused on the restoration of varied
      habitats in order to provide rich biodiversity through ecological
      management. The conservation management of habitats of different levels -
      which contain a wider variety of vegetation - should allow predatory
      birds, such as the barn owl, to exploit habitats at different times of the
      year depending on food abundance. Additionally, measures have been
      suggested t prevent the occurrence of wildlife-vehicle collisions such as
      low flight barriers which would target low flying animals such as the Barn
      Owl. Many studies have outlined the importance of grass verges as foraging
      grounds for Barn Owls, (Taylor, 1994 and Bolger et al., 2001), which
      suggest instead of removing these key foraging grounds and introducing
      manmade structures, conservation efforts could focus on making these
      foraging grounds safer. For instance, the introduction of grass lope
      verges could be used as a wildlife-vehicle collision preventative measure
      in the future.