Impact of land cover characteristics on residential diurnal raptor abundance in the agricultural Sudano-Sahelian region
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Dry-season counts of diurnal raptors were performed in the wet season in the agricultural region in northern Cameroon along several road transects (total = 900 km), while assessing general land cover characteristics and land cover characteristics of the raptor habitats. 9 common diurnal residential raptor species (Milvus migrans, Elanus caeruleus, Melierax metabates, Falco alopex, Butastur rufipennis, Necrosyrtes monachus, Buteo auguralis, Gyps rueppellii, Aquila wahlbergi) have been analyzed for their land cover preference at microhabitat scale regarding several land cover characteristics: agriculture, woodland, village, herbaceous layer, trees and shrubs/bushes. Overall all raptors, except Necrosyrtes monachus and Milvus migrans, showed, on a microhabitat scale level, a significant preference for a high percentage of natural woodland. Conservation of the woodland areas within the agricultural region is thus important for preservation of many raptors: only the scavenging raptors living of dead animals and refuse dumps significantly prefer villages above woodland and agricultural fields. Human presence may not be a problem for several raptors, but their activities might. For cover with agriculture and trees, there is a wide variety in preference, varying from a low level (resp. 0-20% and 0-30 trees/hectare) to a high level (80-100% and >120 trees/hectare). On a microhabitat level, many of the investigated raptors seem to prefer a small cover of herbaceous layer above a larger cover, indicating that on a small scale, grazing can be possibly be positive for raptors, when bare soil is surrounded by areas with more grass. Regarding bush/shrub density, there was little variation in the area (88% having a cover of 0-20%), where only Necrosyrtes monachus and Buteo auguralis showed a significant preference for respectively a low to high cover. Maintaining a diverse landscape with a wide diversity in land cover characteristics is thus expected to be crucial for conservation of raptors. Through field experiments, I investigated the effect of very local land cover characteristics on the presence of prey animals for raptors, during the dry season. Literature shows that a wide variety of food types are eaten by different raptors. Analysis in 4 different land use types revealed that in each land use type, grasshoppers had a statistically significant positive correlation with the grass cover. In natural woodland, average grasshopper numbers found were significantly higher than in villages and cotton plantations. Differences are expected to be larger in the growth season (wet season): in the dry season no significant differences were found between the intensive (cotton) plantations and the extensive (sorghum plantations), regarding grasshopper densities. For other types of prey animals, no significant relations have been found regarding land cover characteristics. Only in general, significantly more lizards were present in villages compared to the other three land use types.