Birds Of Various Species Occupying Burrow Nests In A Mud Wall : (pix Sanjiv Shukla) Royalty-Free Stock Photo

Most burrow nesting bird species dig horizontal tunnels into a vertical (or nearly vertical) dirt or mud cliffs, with a chamber at the tunnel's end to house the eggs. Length of the tunnel varies depending on the substrate and the species. Some make relatively short tunnels (50 to 90 cm), while others can extend for more than three meters. Some ground-nesting species, prefer flat or gently sloping land, digging their entrance tunnels into the ground at an angle.