The discovery of bat droppings is the most common method to prove the presence of a bat roost.
British bats are entirely insectivorous and so their droppings only contain the indigestible parts of their insect prey. This content gives their droppings a crumbly texture which allows them to be differentiated from mouse droppings, which look similar but become very hard when dry.
The characteristics of the droppings i.e. the shape, size and texture, can help to identify the bat species that produced it. You can also use the placement of the droppings (i.e. stuck to a wall or below a beam) to assist in the identification.
Below are some examples of the most commonly encountered bats in South Wales and the UK. If you wish to learn more, the Bat Conservation Trust have produced a pocket-sized guide which is ideal for carrying with you while out surveying. Alternatively, you can read ‘Which Bat Is It’, 1986 Stebbings Robert et al.
These droppings are fine in texture, approximately 1.5-2mm wide, with a length of 7-9mm. Another useful characteristic is that they usually taper at the ends. It is not possible to conclusively differentiate the three species of pipistrelle present in the UK just by the droppings. However, there are some differences. Nathusias pipistrelle droppings are very long and thin like a salami sausage. Common pipistrelle droppings are fine and thin with a smooth appearance. They are the size of a grain of rice. Soprano pipistrelle droppings are very similar to those of common pipistrelles but appear to have a slightly larger girth. All of the droppings can be found in small fragments and can be twisted and jointed. Common and soprano pipistrelle droppings can often be found below the entrance point of a roost such as on exterior walls, windows, sills and doors.
Brown Long-eared Bats
These droppings are bumpy, knobbly in structure, approximately 2.5-3mm in width and 8-10mm wide. The droppings are typically in two or three parts. Brown long-eared droppings are usually located in a line below the ridge beam. They are often found with butterfly and moth wings.
Lesser Horseshoe Bats
These droppings usually consist of two or three loosely joined ovoid shaped sections in a row (like a string of sausages). They are often in a curved or crescent shape. They have a total length of 6-8mm and frequently occur below beams, but only in buildings which have large entrances that the bats can fly through. Sometimes the droppings can be deposited singly or in two and can then be confused with pipistrelle droppings.
Greater Horseshoe Bat
Greater horseshoe bat droppings are often in two parts, very friable and often break down very quickly. The droppings can resemble lesser horseshoe droppings but are bigger and often have a pointed end. The droppings can be found with feeding remains of beetles and moths.
Serotine droppings are coarse in texture, 3.5-4 mm in width and 8-11mm long. They are generally oval shaped with rounded ends and look a bit like a rugby ball. Some droppings have a small pointy end. They are often shiny and glittery. They can be in one or two parts or unusually three. They are most commonly found below the ridge or around the chimney.
Noctule droppings are often matt black in appearance and blunt ended. The droppings often have a strong smell of ammonia when crushed. The species typically roosts in trees and consequently it can be difficult to collect droppings of this species.
Leisler’s bat droppings are similar to noctule but smaller in size. They often appear to have a more pointed end. The droppings often look more sparkly and rippled than noctule droppings.
Whiskered and Brandt’s Bat
Whiskered and Brandt’s bat droppings are typically jointed and form a two or three part dropping. They have a smooth appearance and are mostly black in colour. They often have a spliced appearance with an off-set join running at about 45 degrees. They are mostly found scattered within a roof void and can be mistaken for pipistrelle droppings which are typically found within a roof void.
Natterer’s bat droppings typically have three segments. They are jointed at an offset 45 degree angle. The droppings often have a twisted appearance and look like a plaited rope or a helter-skelter. Small numbers of Natterer’s bats can produce large numbers of droppings. Butterfly and moth feeding remains are often found with the droppings.
Daubenton’s bat droppings appear to be mainly found in three segments. The joints are offset at a 45 degree angle. The droppings are typically jet black, long and bulbous. The droppings smell of river plants when fresh. If water is added to the droppings they turn the water a green colour unlike other droppings which change the colour of water to brown.
Bechstein’s bat droppings have a similar appearance to Natterer’s bat droppings.
Greater Mouse-eared bat
Although identifying bat droppings is a good technique to use to get a general idea of which species are present in a roost, it is not infallible. The texture, colour and size of the droppings can change depending on the food available to the bats. DNA analysis is an option which can provide a definitive answer of the species present. Alternatively, dawn re-entry or dusk emergence surveys can be undertaken so that bat dropping identification can be combined with bat call analysis to get a better picture of the species present.
Our licensed bat survey ecologists undertake all aspects of bat surveys including initial bat scoping surveys, dusk emergence and dawn re-entry flight activity surveys and remote monitoring. For more information call us on 029 2065 0331.
Thanks to Roger Martindale for providing droppings for the different species of bats.
More information about bats and survey techniques can be found in our articles – Bat Droppings, the Bat Year, Architectural Terms for Bat Surveyors, a Guide to Bat Mitigation, Horseshoe Bat Mitigation, Bat Mitigation for Hole/roof-void Dwelling Bats and Bat Mitigation for Crevice-Dwelling Bats.