BREMER P (2012) Nitrophytic lichens on roofs as an indicator of visiting birds. LIMOSA 85 (1): 22-28.

Nitrofytic lichens are common on roofs covered with concrete tiles. Thalli are concentrated at the roof ridges or near chimneys. It was hypothesized that these patterns are caused by the excretions of birds. In a neighbourhood of the city of Zwolle, Overijssel, built in the 1970s, all birds seen on the roofs were counted on average 19 times per month during a full year. On one particular roof, rich in lichen cover, birds were counted and their position on the roof recorded during 6.3 hours of observation. In addition, breeding Starlings Sturnus vulgaris were mapped in the district during four years, to determine whether lichen cover was related to Starling nest locations. During one year, 14 bird species used the roofs for several purposes, the Starling being the most numerous, especially in the breeding season. On the studied roof the lichen cover was correlated with the frequency of visits by Starlings. There was also a significant positive correlation between the number of years in which a particular roof was occupied by breeding Starlings and the lichen cover of the nearby roof tiles. It is concluded that Starlings strongly contribute to the cover of nitrofytic lichens on roofs.

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