Effects and Effectiveness of Supplementary Feeding: an evaluation of population and behaviour patterns in Cirl bunting Emberiza cirlus on Jersey.
Aim: Supplementary feeding is a common strategy used in conservation of vulnerable populations.
However, for supplementary feeding to be most effective, it should be undertaken as a strategic
conservation approach, and include regular evaluation of the strategy’s effects and effectiveness. On
Jersey, supplementary feeding has been implemented since 2011 to support a newly recolonised
population of Cirl bunting Emberiza cirlus. But this strategy has never been formally evaluated. This study
aims to address this by examining how Cirl buntings use the supplementary feeding stations and using the
information gathered to assess whether the current supplementary feeding strategy should continue, and
if so, whether any changes should be made. Additionally, no formal analysis of the long-term population
trend of Jersey’s Cirl bunting population has been made, despite this being information which would
provide context for the supplementary feeding strategy. This study aims to carry out a compilation of all
available population data upon which analysis can be carried out.
Location: Jersey is a small island located in the English Channel. Prior to local extinction at the turn of the
millennium, Cirl buntings bred at multiple sites across the island. However, since the eventual
recolonisation of Jersey by the species in 2011, Cirl buntings have been confined to a single site. The field
study was carried out at this site: a municipal golf course on the east coast of the island.
Methods: The majority of data was collected using camera traps set up on each supplementary feeding
station. These camera gathered data on the frequency, duration and timing of Cirl bunting feeder use as
well as patterns of pair behaviours throughout the survey period. Additional sighting and habitat surveys
were carried out where appropriate. Data analysis was carried out using parametric and non-parametric
versions of correlation and statistical difference tests.
Results: The reported Jersey Cirl bunting population trend of decline-extinction-recolonisation-increase
was confirmed by graphical analysis of the combined population data. This was found not to be
significantly correlated to any climate variables. Regarding the supplementary feeding strategy, use of the
feeding stations was found to decline as the study period progressed. Weather had little to no effect on
patterns of use and one of the clearest factors influencing how the feeders were used was the refill
schedule. Seed was overwhelmingly favoured as a supplementary food source over arthropods, regardless
of weather. Three feeder groups used as individual resource complexes were identified.
Main Conclusions: The factors driving the observed long-term population trends of Cirl buntings on Jersey
are complex and cannot simply be attributed to coupled climate variables. Supplementary feeding may
play an important role in the population increases seen since recolonisation. The existing supplementary
feeding strategy is largely effective. Cirl buntings were not found to be overly-reliant and it is therefore
assumed that sufficient natural food is available during the breeding season. The only changes to the
supplementary feeding strategy suggested are breeding season provision of live mealworms during periods
of wet weather and possible inclusion of another feeder in the southern sector of the golf course, either a
new feeder or a relocated feeder. In the long-term it is recommended that an effective exit strategy is
developed in the event of supplementary feeding no longer being appropriate for Jersey’s Cirl buntings.