Sand martins favour loess: How the properties of loess ground facilitate the nesting of sand martins/bank swallows/uferschwalben (Riparia riparia Linnaeus 1758)

Sand martins/bank swallows (Riparia riparia Linnaeus 1758) nest in tunnels excavated in loess deposits. Loess is particularly suitable because of its cohesive properties, its ease of excavation, its ability to form vertical faces, its ready availability in small scale brick works. A low clay content is a requirement for suitable ground (palaeosols appear to have too much clay), and in sand deposits a low level of cementation. The selective nature of nesting behaviour may have some stratigraphic value, and it may be that loess availability affects the distribution of sand martins (they move away from river banks to brick pits). Soil crust formation may affect the inhabitability of nest tunnels (the same phenomenon may be important in loess deposit formation). Penetration resistance of the ground is required to be in a middle-range, not too hard, not too soft. This is the Heneberg compromise: a compromise between tunnel stability and ease of excavation and construction.