Using Dietary Analysis and Habitat Selection to Inform Conservation Management of Reintroduced Great Bustards Otis tarda in an Agricultural Landscape

Capsule: Reintroduced Great Bustards achieve dietary and habitat diversity despite living in an intensive
agricultural setting.
Aims: To investigate dietary composition and habitat use of reintroduced Great Bustards Otis tarda released
in southwest England and the impact of supplemental feed on autumn dietary selection.
Methods: Faecal samples were collected from a mixed group of free-ranging bustards without (July 2012,
May, September, and November 2013) and with (October and December 2012) access to supplemental
feeds. Concurrently, diurnal land use observations were recorded for all months but September and
December. Composite monthly faecal samples were micro-histologically analysed to assess dietary
composition. Year-round landscape-level habitat use was determined using re-sightings and satellite
telemetry data for birds surviving more than 182 days post-release. Generalized linear models were
used to test for differences in habitat selection across the year, by sex and within and outside release
areas for each habitat type, and habitat diversity was quantified using the Shannon–Weaver Index.
Results: Dietary composition varied depending on plant availability and phenological stage, and
invertebrates were rarely selected. Agricultural crops – primarily oil-seed rape, mustard, barley grass,
lucerne, and barley seed – comprised the bulk of the diet, but grassland and weedy forbs were always
important secondary foods (>25%), except when provided extruded pellets. Monthly changes in habitat
use suggest sex-based habitat segregation, with females living in higher habitat diversity settings.
Grasslands were used across the year. When supplemental food was provided, it came to dominate
dietary intake.
Conclusion: Great Bustards can adapt to an intensive agricultural setting, but require unrestricted access to
adjacent grasslands. They would be best served with small-scale habitat mosaics. If supplemental foods are
to be provided to juvenile birds, quantities must be limited and the birds weaned off before dispersal to
maximize reintroduction success.