The Assynt Leisure Centre has been hosting this spring a series of workshops by the Field Club on aspects of local wildlife. Andy Summers kicked off on 24th February with Sea Birds and Gwen Richards followed on 12th March with Animal Tracks and Signs. On 19th March it was my turn, with Small mammals and owl pellets.
The first part of the workshop was an introduction to the eight species of smaller mammals that may form part of the diet of local owls: shrews (common, pygmy and water); mice (wood, with house for comparison) and voles (bank, field and water, with brown rat for comparison with water vole). House mice now only rarely occur locally.
This was followed by a short session on the diagnostic features of the skulls of these prey species, based on a customised hand-out and the superb illustrations in A Photographic Guide to Small Mammal Remains in Barn Owl Pellets (S.J. Ramsay and D. Crawley, 2022, published by the Natural History Museum and Mammal Society; photo 1).
Results
Jane Livingstone had kindly collected on 5th March a sample of recent barn owl pellets (photo 2) from a derelict house on Druim na Claise, Clashmore (NC0430), having ascertained that the owls were not in residence.
Eight pellets were enthusiastically dismantled by the participants (photos 3-6) and the final tally of the prey was nineteen field voles, five common shrews and one pygmy shrew. We did not have any previous records of either common or pygmy shrews from the 1km square in which the pellets were collected.
I later photographed some of the skulls extracted, illustrating the following diagnostic features (photos 7-14). Field vole: tooth rows with gap between incisors and cheekteeth; sharp-edged zig-zag cheekteeth with open roots. Common and pygmy shrews: continuous rows of red-tipped teeth; skull and lower jaw of pygmy shrew shorter than common (jaws 10/12 mm).
As a matter of interest, I weighed eight pellets; they were 6-9 cm long and totalled 82 gms. The average live weight of the prey species is about 35 gms for field voles, 12 gms for common shrews and 5 gms for pygmy shrews, giving a total weight of 730 gms for the 25 prey items; very nutritious.
Ian M. Evans
Photos 3-4 by Gwen Richards, others by Ian M. Evans