Month: March 2018
One of our supporters has drawn our attention to this superb piece of writing by American novelist and columnist Jonathan Franzen. It’s about why birds matter and although many of the references are to New World species, the sentiments are universal.
Thanks to Sam Crofts for this overview of the work he’s been doing with Little Owls in the county…
Being a keen birder and ringer when the opportunity to study Little Owls for my MSc thesis presented itself I jumped at the chance. Little Owls are a species exhibiting dramatic population declines of -57% in the U.K since 1994 and have been listed as a species of conservation concern in Europe. As the Little Owl was introduced to the U.K in the 1800s it is classified as an introduced breeder and therefore comparatively receives limited research and conservation attention compared with other species. A number of factors have been associated with the decline of Little Owls. Changes in land management practices, in particular agricultural intensification have led to the destruction of old orchards as well as removal of hedgerows and old growth trees that the owls use for nesting. The use of pesticides has also been suggested to reduce insect availability, a primary food source of the owls. Studies have investigated the habitat and diet of the Little Owl however the majority have focused on European populations and have not investigated the relationship between these two abiotic factors.
With the amazing enthusiasm of Gloucestershire Raptor Monitoring Group (GRMG) and multiple land owners I was able to conduct habitat surveys around nest sites and collect pellets to analyse habitat and diet. Phase 1 habitat surveys were conducted to classify parcels of land within a Little Owl territory according to vegetation composition. The height of vegetation was also recorded as it has been documented to influence hunting strategy. The remains of beetles and small mammals in pellets were identified to the species level where possible by Linda Losito and Bob Cowley. The data gathered was then combined to examine how habitat influences Little Owl diet.
The habitat surveys supported the findings of multiple studies from Europe suggesting that orchards and improved grasslands were the favoured habitat of UK little owls. A preference for short grazed grassland was also observed. However, territories contained a greater area of arable land on average when compared to reports from Europe. Analysis of habitat variation within the study sites revealed the majority of variation between sites could be accounted for by differing areas of improved grassland and arable. Using this information comparison of diet was then conducted between categories of sites defined by their habitat compositions. These categories were; sites dominated by improved grassland, sites with a large area of arable and sites with an intermediate mix of the two. In total beetle remains were identified into 43 categories, the majority of these being species however, in some cases it was only possible to attribute remains to a genus (Table 1).
There was no significant difference in either the quantity or number of insect species consumed between these categorisations of site habitat. There was however, a significant correlation between sites with a greater area of arable and increased consumption of small mammals, both in terms of quantity and number of species consumed. The height of vegetation within parcels of habitat was also quantified. When this data was compared with dietary information, a positive correlation was observed between the area of short grassland at a site and the quantity of beetles consumed. These results suggest a heterogeneous habitat dominated by short improved grassland, most probably grazed, alongside arable crops and old growth trees providing cavities for nesting are the most suitable for Little Owl territories. These findings add weight to suggestions that changes in land use could be driving Little Owl population decline. With widespread agricultural intensification heterogeneous landscapes are less common as was previously the case, potentially reducing the availability of optimal nesting sites and suitable hunting grounds.
Using the data gathered on habitat preferences in combination with land use data from the Centre for Ecology and Hydrology a model was produced to establish potential locations with suitable habitat for Little Owl nest sites in Gloucestershire. Suitable habitat was defined as areas dominated by improved grassland adjacent to smaller patches of arable. The locations of traditional orchards were also included as these provide excellent nesting opportunities. Areas close to main roads were also excluded, with a variety of exclusion distances being tested. This model was then validated against actual Little Owl sightings (figure 1). As can be seen the greatest concentration of traditional orchards and larger parcels of suitable habitat occur in the West of the county, it is also here that the greatest concentration of sightings occur. The more intensively farmed Cotswolds in the east have fewer orchards and smaller parcels of suitable land as well as fewer sightings of Little Owls. Statistical validation of the map and sightings revealed a correlation between predicted suitable habitat and actual Little Owl sightings.
Figure 12 Map of suitable Little Owl habitat within Gloucestershire. Minor roads buffer of 25 m and major roads (A, B and Motorways) buffered at 263.4. Reported Little Owl sightings included for validation of suitable habitat model.
Examination of pellets uncovered the alarming discovery of plastic items consumed by Little Owls. Items found ranged from short pieces of plastic binding to clothing tags. These pieces were found in pellets from sites closer to settlements demonstrating the damage our waste has on the environment.
A great deal of thanks is expressed to all those who assisted this project and the hope is that information gathered can assist the great work being undertaken by GRMG in conserving Little Owls in Gloucestershire.
Table 1. Beetle species list