Unforeseen effects of ecosystem restoration on yellow-legged gulls in a small western Mediterranean island

Abstract

A conservation project aimed at ecosystem restoration had several unforeseen effects on a colony of the yellow-legged gull Larus michahellis in a small western Mediterranean island (Benidorm Island). The project included regulation of massive tourist visits to help restore the soil and autochthonous vegetation. However, gulls habituated rapidly to regulation of tourist activities, as nests located either close to or far from the main trail showed a similar hatching success. The quiet conditions produced by regulation seemingly facilitated a rapid colony increase. Partial removal of alien vegetation (Opuntia maxima) showed that gulls had a preference for sites with high vegetation cover because the growth of the colony was proportionally larger in well-vegetated plots. The pricking of a large number of gull eggs surprisingly coincided with a high reproductive success compared to the previous year, although indicators of food availability remained constant between years and the colony had decreased in numbers. Untreated nests were probably more successful because territory size for chicks increased and intraspecific predation decreased. Extreme care must be taken when planning ecosystem-wide management on islands with yellow-legged gull colonies, or other gull species locally considered as pests, to prevent unwanted effects.