Can mismatches between habitat preferences and nest survival cause ecological traps for birds in intensive Mediterranean farmland?

Landscape intensification might cause conditions that organisms perceive as suitable, but where reproduction or survival is insufficient to maintain self-sustaining populations. The strict criteria required for proving such ecological traps are hard to fulfil in practice, requiring simpler approaches to identify species vulnerability to ecological trapping. This study focused on five bird species of conservation concern inhabiting Mediterranean farmland to evaluate vulnerability to ecological traps resulting from (i) mismatches between habitat preferences and nest survival (i.e. field and landscape types with high or low nest survival), and (ii) the incapacity of risk avoidance (i.e. negative responses to predator abundances or nest failure rates).

Nest predation and livestock trampling rates were highest in fields with short and sparse swards, suggesting that these were the least safe for nesting grassland birds. Abundance of important predator species (e.g. Egyptian mongooses) showed positive relations with nest predation rates. Corn buntings and fan-tailed warblers were associated with tall and dense swards, tawny pipits, Galerida larks and short-toed larks with short swards; landscape context had only minor effects on bird densities. Tawny pipits and Galerida larks avoided fields with high nest predation rates and high mongoose abundance, respectively, whereas short-toed larks were positively associated with high nest predation rates.

Our approach suggests that the short-toed lark may be more vulnerable to ecological trapping than the other species selecting safe habitats or showing risk avoidance. Management actions increasing nest survival at short sward fields will likely favour grassland bird conservation in intensive Mediterranean farmland.