Barn owls’ pellets help track invasive shrew’s spread on Teesside

The study, conducted at RSPB Saltholme on Teesside, was carried out by the Mammal Society as part of its ‘Searching for Shrews’ project, now in its third year.

Ian Bond, a Northumbria Mammal Group volunteer, said: “So far, the Great White-toothed Shrew has not arrived at Saltholme, but what we have learned about other small mammals in the area is perhaps even more interesting.

Owl pellet analysis (Image: Derek Crawley)

“At Saltholme, Barn Owls have been preying on every other species of small mammal that is found in Northeast England, ten different species in total.

“Due to the near demise of Water Voles elsewhere and the patchy distribution of some of the other small mammal species, this is almost certainly the only place in the region where Barn Owls can choose from such a wide menu”.

The reserve is just 12km from the nearest known record of the greater white-toothed shrew, first recorded in the Sunderland area in 2022.

Pygmy shrew (Image: The Mammal Society)

RSPB staff have been collecting pellets every three months since October 2025, and the presence or absence of the invasive shrew is considered important due to its potential impact on native shrew populations.

Barn owls are a valuable tool for this kind of research, as they swallow their prey whole and later regurgitate pellets made of indigestible bones and fur.

These pellets provide a non-invasive way to monitor small mammal populations and identify species living in the area.

Chris Francis (Image: Claire Freeburn)

Chris Francis, senior reserve manager at RSPB Saltholme, said: “These findings demonstrate the habitats we’ve created and continue to manage at RSPB Saltholme are providing homes for a great variety of small mammals, such as Water Voles, Harvest Mice and Water Shrews.

“There’s a good deal more to learn and when it comes to surveying them, nothing beats an Owl to tell us about what’s here. Of all the birds that are seen at Saltholme, nothing excites visitors more than seeing a Barn Owl hunting over the meadows. Beautiful to look at and so well adapted as a hunter.”

Water shrew remains were found in high numbers, with Saltholme accounting for more than a third of all water shrew remains in the North East survey, despite contributing just over a tenth of the total pellets examined.

This highlights the value of the reserve’s managed mix of wetland and grassland habitats.

Barn Owl (Image: Supplied)

The only small mammal species native to the North East not found in the pellets was the greater white-toothed shrew.

Other species more widely found in England but absent from Saltholme include the hazel dormouse, fat dormouse, and yellow-necked mouse.

Saltholme currently supports four pairs of barn owls, with one pair successfully fledging seven chicks this year.

Dissecting owl pellets (Image: Kate Larson)

Mr Bond said: “The Barn Owl is one of Britain’s most recognisable birds, famed for its ghostly silent flight and heart-shaped face. At Saltholme, the pellets they leave behind give us a fascinating picture of the small mammals living on the reserve, while helping us monitor for the arrival of the Greater White-toothed Shrew.”

The Mammal Society’s North East group has examined owl pellets from more than 50 locations across the region as part of the wider project.

The continued absence of the greater white-toothed shrew at Saltholme is seen as significant, given the reserve’s proximity to known populations and its suitability as a monitoring site for the species’ potential spread.