Talk Is it possible to relocate a cormorant roost affected by new transport infrastructures

The largest great cormorant (Phalacrocorax carbo) wintering roost in the Llobregat Delta (Barcelona) is located in a group of trees in the old riverbed of the Llobregat River, which was diverted as a consequence of the works to enlarge Barcelona’s port. In the last 10 years, an average of over 250 individuals used this roost, i.e. 59% of all individuals in the Llobregat Delta. The future railway and road accesses to the port will be located in the old riverbed, and the roost will disappear. To reduce the impact for this bird species, Barcelona Port Authority is developing an innovative project to provide alternative artificial roosts, and to prevent uncontrolled dispersion of cormorants searching for new places to stay. This could be a hazard for aviation safety, as Barcelona international airport is located in the vicinity of the port. This long-term project started in 2006, when several designs of artificial structures were tested. The most effective was a structure that simulates a tree. It is 10 m high, with a mast and up to 10 horizontal branches. In a second step, suitable locations for alternative roosts – the previous selection was based on knowledge of cormorants’ ecological requirements – were equipped with groups of this kind of artificial structures, and a monitoring plan was started. For each wintering period (October–April) from 2006/2007 onwards, monthly censuses were conducted in the different roosts in the Llobregat Delta. The censuses consisted of two hours of observation around dusk, when individuals were counted as they reached the roost to spend the night. In roosts where artificial structures were placed, it was recorded whether or not the cormorants rested in these structures or in trees. The use of artificial structures has increased steadily over the years. In 2006/2007, the percentage of cormorants wintering in the Llobregat Delta that roosted in artificial structures was about 5%, while in the 2014/2015 winter, a maximum of 79% of individuals roosted in artificial structures was achieved. During the last winter, 73% of cormorants roosting in the old riverbed preferred to use the artificial structures, although no trees had been removed. In 2016, new structures are going to be placed in a restored wetland area, and Barcelona Port Authority is launching a communication campaign that includes an informative video, leaflets and other materials. This experience shows that providing artificial resting structures in suitable places – even where no previous roost was established – can reduce disturbances to birds caused by the construction of new infrastructure. This successful, innovative approach to a human wildlife conflict has been the result of strong cooperation between engineers and experts on wildlife and ecology. Although measures must be adapted to every species and scenario, this experience is intended to be an example for future situations involving infrastructures and other bird species.

cormorant roost; Barcelona’s Port; mitigation measure; infrastructure construction