BCD 2017

148 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 7 BIRD and BAT GUANO and its effect on conservation and maintenance TIM HUTTON, DAVID WATT and JENNY BROWN ‘G UANO’ CAN be defined as the accumulated droppings of fish-eating birds and originally referred to the large deposits of this material found in coastal South America (the term’s origin is the Andean Quechuan word for dung, huano ). Because of its high nitrate content it was commercially mined in the past for use in fertilisers and the manufacture of explosives. It has also come to be used to describe accumulations of bird or bat faeces in the built environment. As well as marring a building’s appearance, guano can cause health problems, physical damage, restriction of access and chemical and biological damage or decay, both on the exterior of buildings and internally. The extent of additional water penetration into the guano is very important, as this may mobilise the chemicals in the material resulting in accelerated corrosion or decay. Dry material may represent an increased health hazard due to inhalation of fungal spores or other potential allergens and pathogens in airborne dust. It must be noted that measures taken to remove guano from buildings may be more harmful to the building than the deposits themselves. As in all cases of building pathology it is necessary to take a holistic view of the affected structures and environments in order to properly diagnose the associated problems and to devise cost-effective remedial and risk management measures. This is especially true in the potentially difficult legal and public relations environment of bird and bat control. SOURCES Probably the main source of guano in the built environment in the UK is feral pigeons ( Columba livia var ). They use buildings for roosting, nesting and for ‘loafing’ while feeding. Their activities result in blockage of roof drainage systems – one of the most significant causes of damp and decay in historic buildings, costing millions of pounds each year and destroying historic fabric. Other bird species roosting in buildings include starlings and gulls, and many others may use vantage points on buildings and other townscape features as a perching point, particularly in areas where food might be available. Many species of bat also occupy buildings for roosting, breeding and hibernation. In the UK, accumulations of bat guano tend to be relatively small compared to those left by birds, but they can adhere to vertical surfaces, such as around openings where bats exit a building. Bat droppings can be distinguished from small rodent droppings as they are composed predominantly of digested insects and can be easily crumbled. However, large accumulations of droppings pose a particular issue and may require surfaces to be protected. VULNERABLE STRUCTURES Any structure suitable for occupancy by birds or bats may be subject to the accumulation of guano. Even small structures or small localised parts of structures may be affected. For example, parts of monuments or statuary used for perching by pigeons or seagulls can be heavily contaminated, resulting in severe localised aesthetic, physical and chemical effects. However, the most vulnerable structures are generally those which are poorly accessible or relatively undisturbed, especially in unoccupied or partially occupied buildings. In all cases, the availability of food sources is likely to be a significant factor. Although both birds and bats may travel surprisingly long distances in order to feed from a A gull perches atop Alfred Drury’s 1901 statue of the theologian Richard Hooker at Exeter Cathedral (Photo: Jonathan Taylor)