Blog by Emily Goldstein
My name is Emily Goldstein and I came to Ireland from Boston, Massachusetts to study squirrels for my PhD in the School of Biological, Earth and Environmental Sciences in University College Cork. This might sound like a strange thing to do – most people in Ireland rarely see squirrels in their daily lives. However, there are some fascinating things going on with squirrels in this country. The native squirrel species in Ireland is the red squirrel – it has been present here since the end of the last ice age. The grey squirrel, however is an invasive alien species and competes for food and habitat resources with the native red squirrel.
The expansion of the grey squirrel’s geographic range in this country has proceeded more slowly in this country than it has in Britain. I used a citizen science survey to collect public sightings of both squirrel species in Munster to find out where the invasion frontier of the grey squirrel was. You can see the current sightings map using the species viewer on the National Biodiversity Data Centre’s map page (http://maps.biodiversityireland.ie/#/Home). Once I had found the invasion frontier I studies two populations of grey squirrels on the frontier in-depth with a two-year intensive live trapping programme. During these two years I captured, studied, and released 131 individual squirrels during over 1,000 squirrel capture events. Repeat measurements from individuals over a period of time can give valuable information on population functioning.
I found that grey squirrel populations at the invasion frontier do function differently than grey squirrel populations in established areas or in the native range of the species in North America. For instance, populations at the invasion frontier have higher birth rates showing that the populations are increasing. Annual survival of grey squirrels is higher in introduced populations than in the native range in deciduous forest habitat but is lower in mixed or coniferous habitat. The highest reports of annual grey squirrel survival are recorded in Britain where the grey squirrel invasion has been more dramatic than in Ireland. Grey squirrel population density is also lower at the invasion frontier than it is in established populations as would be expected.
Other research on squirrels in Ireland has shown that there is a correlation between recovering pine marten numbers in the Midlands and a decrease in grey squirrel numbers. Encouragingly, red squirrels are also returning to these areas. Further study is needed to better understand the relationship between these events and on how to best control grey squirrel population numbers going forward to protect the native red squirrel.
You can read more about my research in these published scientific papers feel free to contact me at firstname.lastname@example.org if you would like a pdf copy:
Goldstein EA, Butler F, Lawton C. 2014. Frontier population dynamics of an invasive squirrel species: Do introduced populations function differently than those in the native range? Biological Invasions. http://link.springer.com/article/10.1007/s10530-014-0787-x
Goldstein EA, Lawton C, Sheehy E, Butler F. 2014. Locating species range frontiers: a cost and efficiency comparison of citizen science and hair-tube survey methods for use in tracking an invasive squirrel. Wildlife Research 41(1): 64-74. http://www.publish.csiro.au/nid/144/paper/WR13197.htm