Spatial ecology of grey squirrels (Sciurus carolinensis) in an urban environment

  • Devin Fitzpatrick

Student thesis: Master's ThesisMaster of Research (awarded by UHI)


The North American eastern grey squirrel (Sciurus carolinensis) is a
highly invasive species that has replaced the sympatric native Eurasian red
squirrel (Sciurus vulgaris) across much of the United Kingdom through
exploitative competition and disease spread. The city of Aberdeen remains a
stronghold for the grey squirrel in Scotland, and Saving Scotland’s Red
Squirrels (SSRS) has identified lack of access to perform control in private
gardens as a potential barrier to eradication of the species from this urban
area. Successful eradication requires (i) all individuals of a population to be
vulnerable to control efforts, (ii) the rate of removal of individuals to exceed
the rate of population growth, and (iii) immigration into the population to be
zero. Development of effective management and control strategies for grey
squirrels meeting these criteria is currently hindered by significant gaps in
knowledge of urban grey squirrel spatial ecology, as highlighted by a
systematic literature review, with no previous studies estimating home ranges
in residential areas or quantifying space use and habitat preference at the
individual level. This thesis aims to address this firstly by estimating the home
ranges of 10 individual grey squirrels, tracked using GPS telemetry for up to
five months in Aberdeen, and assessing habitat selection within these home
ranges. This information is used to determine the distribution of traps required
to put each individual of the target population at risk of coming into contact
with a trap within various habitat types. Secondly, environmental factors and
trapping procedures, such as pre-baiting, which are likely to influence trapping
success for grey squirrels are, assessed through analysis of 12 years of
historical trapping data from Aberdeen provided by SSRS. Results of this
research suggest that trapping in private gardens is not necessary to the
eradication of the species from Aberdeen; not one of the tracked grey
squirrels’ home ranges falls entirely within residential habitat and the
individuals exhibit a preference for woodland habitat. SSRS resources should
be allocated to concentrating grey squirrel trapping in broadleaved and mixed
woodland compartments throughout the city, with traps spaced no more than
150 metres and 190 metres apart in these habitat types, respectively. Traps
should be pre-baited for two weeks and trapping effort should be increased in
late spring and early summer, to ensure rate of grey squirrel removal exceeds
rate of population growth following the winter breeding season, and in early
winter, when availability of natural food resources is low.
Date of Award9 Feb 2023
Original languageEnglish
Awarding Institution
  • University of the Highlands and Islands
SupervisorMelanie Smith (Supervisor)

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