Abandoned pastoral settlements provide concentrations of resources for savanna birds

Knowledge is poor of how fertilization affects birds in grasslands. We investigated the impact on birds of abandoned pastoral settlements that historically received very high levels of livestock dung. A total of 28 abandoned settlements and 74 landscape controls - in Koyake Group Ranch and Maasai Mara National Reserve in Kenya - were surveyed for birds during the wet and/or dry season. Our results showed that bird species richness and total abundance increased within 200 m of abandoned pastoral settlements, particularly during the dry season when foraging resources on the savanna are limited. The high concentrations of nutrients inside abandoned settlements favoured the abundance of Diptera and Coleoptera, as shown by invertebrate surveys performed during the dry season on a subset of 32 sites. Both total numbers and dry biomass of these two invertebrate orders were higher on abandoned settlements in comparison with the surrounding landscape. We conclude that higher fertilization levels cause a temporal and spatial redistribution of birds on the savanna. Livestock fertilization and bird abundance are probably linked through an increase in abundance of invertebrate food upon which birds feed in an opportunistic fashion.