Predation and shorebirds: predation management, habitat effects and public opinions

• Main Author: Isaksson, Daniel
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2009
• Subjects: Conservation; waders; predation; coastal pastures; redshank; lapwing; attitudes; human dimensions; Vanellus vanellus
• Online Access: http://hdl.handle.net/2077/18848

Many shorebird populations are rapidly declining and a high nest predation rate is one of the threats facing these populations. Thus, factors that affect predation and how to manage it in an effective way are receiving increased attention. This thesis deals with nest predation in two ground-nesting shorebirds (waders): the Northern lapwing Vanellus vanellus, and the redshank Tringa totanus nesting in coastal pastures. I study how habitat structures affect nest predation and distribution. I also test the effectiveness of two non-lethal methods for managing predation, and survey public attitudes towards predator control and animal conservation. Predators that hunt by sight often search for prey from elevated perches, such as trees, stone walls and fences. Theory suggests that prey visibility depends strongly on predator perch height and distance. I estimated how prey (a mounted bird) visibility depends on predator perch height, distance and vegetation height in coastal pastures. Visibility increases strongly with observer perch height and proximity. For example, from the lowest perch (0.2 m), visibility of the target bird declines to < 5% beyond 20 m distance, but 40% of it remains visible from the highest perch (8 m), even as far as 120 m. The strong increase of prey visibility with predator search height suggests that the removal of predator perches can improve the survival of endangered prey populations in open habitats. Predators such as the hooded crow Corvus cornix use raised structures for perching and to elude lapwing attacks. I find that crows spent more time at or near raised structures than expected and that wader nests were placed farther away from these structures than expected in two out of three years. Waders thus tend to avoid breeding close to raised structures, which therefore reduces the suitable breeding area and probably also the local wader population size. Habitat management is just one technique for reducing nest predation, and apart from lethal predator control, there are several ...