Individual and demographic responses of a marsh bird assemblage to habitat loss and subsequent restoration

Background  The alteration and loss of habitats are two of the main threats that biodiversity conservation is currently facing up to. The present study describes the effects of a perturbation and restoration in a reedbed habitat on a bird assemblage. We studied the bird community of a wetland of central Spain between 1995 and 2009, during which time an anthropic perturbation altered the original structure of the habitat; subsequently, as a result of restoration works, the habitat returned to its original state.

Methods We evaluated the effects on six population and physical parameters of the birds at three different phases of their life cycles (breeding, wintering and post-breeding migration seasons) before, during and after the habitat alteration. GLM was used to analyze the influence of three independent variables (year, perturbation phase and temperature).

Results The relative abundance and the species richness values decreased when habitat was altered, but then recovered as a result of the regeneration works. This pattern was the clearest amongst specialist species. Breeding success also declined during the perturbation phase and then increased; likewise, the sex ratio changed given that the proportion of male birds increased when habitat was altered. These results are discussed in relation to changes on availability of resources in altered habitats, to the adaptive mechanisms in the exploitation of ecological requirements and to the selection of optimum and sub-optimum habitats by generalist and specialist species.

Conclusions  Ecosystem restoration can favour the recovery of population indexes of specialist passerines, although it depends on the efficiency of the type of restoration activity performed and on the complexity of the habitat.