Conservation of Heritage Sites in Kathmandu, Nepal: Assessing the Corrosion Threat from Pigeon Excreta on Metal Monuments

Pigeons have long been a common nuisance at numerous cultural sites in the Kathmandu Valley. Besides the health, economic and aesthetic issues caused by the pigeon excreta, this waste may also result in damaging effects to the materials used in Nepalese architecture, including metals such as copper and its alloys. This study assessed the impact of pigeon excreta on the metal-based monuments of cultural importance in the Kathmandu Valley. To test the corrosive effects of the excreta, fresh pigeon excreta were collected from three world heritage sites located around the Kathmandu Valley: Kathmandu, Bhaktapur, and Patan Durbar Squares. Additionally, metal samples, like those used in the monuments (including copper and its alloys bronze and brass), were obtained from metal shops in the surrounding area of Patan Durbar Square. The metal samples were cleaned, weighed, and immersed in pigeon excreta and placed in covered beakers for a duration of 122 days. During this study period, the metal samples were cleaned and weighed at multiple intervals during three designated exposure periods: Short-term duration (<10 days), Medium-term duration (10-42 days) and Long-term duration (42-122 days), to evaluate the degree of corrosion. Analysis of the metal samples showed a significant corrosion loss in copper but not in the alloys bronze and brass, thus indicating a stronger negative impact of pigeon excreta on copper compared to its alloys. Therefore, the use of copper-alloys instead of pure copper in monument renovation could serve as a useful alternative to help minimize the adverse effects of pigeon excreta. These findings provide an important insight in helping to promote the long-term preservation of cultural heritage sites.