Tawny owl diet in Lochinver
On 26th February 2023, Bel Harkin showed us two owl pellets that had been deposited in her back garden in Inverpark, Lochinver (photo 1, NC089230). Her nephew, Fraser Lang, had previously taken a photo on his phone of a tawny owl perched on wires just beyond the garden, so that seemed a likely source (photo 2). A quick look showed what appeared to be small mammal bones (photo 3), so we collected the pellets to take them to bits.
Closer examination revealed the skulls (photo 4) and other bones of two voles. The larger skull had molar teeth with sharply-angled cusps and open roots. To be technical, the upper second molars also had an additional cusp on the inner side (photo 5, from reference below). These features are diagnostic of field voles, a frequent prey species of tawny and other owls.
Field Voles
Field voles are probably the most numerous small mammals in Assynt, found in suitable habitat (especially tussock grassland and rushes) throughout the parish, sometimes quite high up the hills. They are the favourite food of a wide range of predatory birds and mammals, including domestic cats in built-up areas. In life, they have short tails and rather nondescript brown fur (photo 6).
The second, slightly smaller, skull had molar teeth with more rounded cusps and closed roots, and was that of a bank vole. Records of bank voles are much sparser in Assynt, mainly from cat kills or owl pellets around the coast (working map, photo 7), so these pellets provide useful information.
Bank Voles
Bank voles appear to prefer gardens, scrub and woodland, and may not venture far into moorland habitats. There are photos of them raiding garden bird feeders, including one at Inchnadamph (photo 8). In life, their tails are rather longer than those of field voles and their fur has a rich chestnut tinge.
There seems to be no reference in the national literature to the apparent size difference between the skulls. So, out of curiosity, the lengths of the molar tooth rows were measured with a micrometer eyepiece on the microscope: 5.7mm in the field vole and 4.9mm in the bank vole, which was gratifying.
Ian M. Evans and Gwen Richards
Reference. A history of British mammals Barrett-Hamilton G.E.H. et al., 1910-1921. London, Gurney and Jackson (issued in parts).
You can read more about owl pellets here