A number of bird species use man-made structures as day-perches as well as overnight roosts and nesting sites. Notable species which engage in this activity are Starlings, Pigeons (Rock Dove) and various gull species.
Problems associated with this activity most frequently involve accumulated droppings, and the resulting odour , unsanitary and possibly hazardous conditions associated with falling bird droppings on walkways and even pedestrians. Additionally, accumulated bird droppings contain nutrients which promote moss and lichen growth on roof felt and asphalt shingles, resulting in property-damage from premature shingle and roof covering deterioration.
The only permanent remedy to prevent mass roosting is by exclusion. The installation of excluder devices and modifications will prevent the birds from perching. This is best accomplished by the installation of raised monofilament lines or fine stainless wires or sloped ledge guards along perch areas, and modifying ledges and railings to a slope that inhibits perching (about 60E pitch).
In instances where the installation of such excluders is not practical or possible, such as the problem of gulls landing on flat roofs, the use of deterrent devices may eliminate the problem. The use of eyeball balloons and other wind-activated devices may resolve such occurrences.