Camera trap grey squirrel photograph data

Effective wildlife population management requires an understanding of the
abundance of the target species. In the UK, the increase in numbers and
range of the non-native invasive grey squirrel Sciurus carolinensis poses
a substantial threat to the existence of the native red squirrel S.
vulgaris, to tree health, and to the forestry industry. Reducing the
number of grey squirrels is crucial to mitigate their impacts. 
Camera traps are increasingly used to estimate animal abundance, and
methods have been developed that do not require the identification of
individual animals. Most of these methods have been focussed on medium to
large mammal species with large range sizes and may be unsuitable for
measuring local abundances of smaller mammals that have variable detection
rates and hard-to-measure movement behaviour. The aim of this study was to
develop a practical and cost-effective method, based on a camera trap
index, that could be used by practitioners to estimate target densities of
grey squirrels in woodlands to provide guidance on the numbers of traps or
contraceptive feeders required for local grey squirrel control. Camera
traps were deployed in ten independent woods of between 6 and 28 ha in
size. An index, calculated from the number of grey squirrel photographs
recorded per camera per day had a strong linear relationship (R2 = 0.90)
with the densities of squirrels removed in trap and dispatch operations.
From different time filters tested, a 5 minute filter was applied, where
photographs of squirrels recorded on the same camera within 5 minutes of a
previous photograph were not counted. There were no significant
differences between the number of squirrel photographs per camera recorded
by three different models of camera, increasing the method's
practical application. This study demonstrated that a camera index could
be used to inform the number of feeders or traps required for grey
squirrel management through culling or contraception. Results could be
obtained within six days without requiring expensive equipment or a high
level of technical input. This method can easily be adapted to other
rodent or small mammal species, making it widely applicable to other
wildlife management interventions.