Ralph Buij

Impacts of Roads, Hunting, and Habitat Alteration on Nocturnal Mammals in African Rainforests

Nocturnal mammals are poorly studied in Central Africa, a region experiencing dramatic increases in logging, roads, and hunting activity. In the rainforests of southern Gabon, we used spotlighting surveys to estimate abundances of nocturnal mammal species and guilds at varying distances from forest roads and between hunted and unhunted treatments (comparing a 130-km(2) oil concession that was nearly free of hunting, with nearby areas outside the concession that had moderate hunting pressure). At each of 12 study sites that were evenly divided between hunted and unhunted areas, we established standardized 1-km transects along road verges and at 50, 300, and 600 m from the road. We then repeatedly surveyed mammals at each site during 2006. Hunting had few apparent effects on this assemblage. Nevertheless, the species richness and often the abundance of nocturnal primates, smaller ungulates, and carnivores were significantly depressed within approximately 30 m of roads. Scansorial rodents increased in abundance in hunted forests, possibly in response to habitat changes caused by logging or nearby swidden farming. In multiple-regression models many species and guilds were significantly influenced by forest-canopy and understory cover, both of which are altered by logging and by certain abiotic variables. In general, nocturnal species, many of which are arboreal or relatively small in size (<10 kg), were less strongly influenced by hunting and more strongly affected by human-induced changes in forest structure than were larger mammal species in our study area.

Breeding Performance of the Grasshopper Buzzard (Butastur rufipennis) in a Natural and A Human-Modified West African Savanna

Abstract. Few studies have examined raptor reproduction in response to land-use change in sub-Saharan Africa, hampering conservation efforts to address regional declines. To further our understanding of mechanisms underlying the dramatic declines of West African raptors, we examined the relationship between environmental conditions, nest density, and measures of reproduction in the Grasshopper Buzzard (Butastur rufipennis). Analyses were based on 244 nest sites divided between transformed and natural habitat in northern Cameroon. At the landscape scale, nest density increased with the density of preferred nest trees. Nests were more widely spaced in transformed than in natural habitat. Dispersion was adjusted to differences in availability of small mammals, which was negatively associated with distance to nearest neighbor, and in the area under cultivation, which was positively associated with distance to nearest neighbor. Productivity was positively associated with rainfall, canopy shielding the nest, availability of grasshoppers, and the nests visibility from ground level; canopy shielding, grass cover, rainfall, and distance to nearest neighbor were positively associated with nest success. In natural habitat, losses of eggs and nestlings to natural predators were greater than in transformed habitats, while losses through human predation were small. Productivity and nest success were unaffected by land use because of the opposing effects of greater predation pressure, closer spacing of nests, and more food in natural habitat than in transformed habitat. Thus transformed habitat may provide adequate breeding habitat for the Grasshopper Buzzard, but declining rainfall and intensifying anthropogenic land use are likely to affect future reproductive output.

Raptor habitat use in the Lake Chad Basin: Insights into the effect of flood-plain transformation on Afrotropical and Palearctic raptors

West African flood-plains have undergone major land-use transformations in the second half of the 20th century. To obtain insight in the effect of flood-plain development for irrigated rice cultivation on the abundance, richness, and diversity of Palearctic and Afrotropical raptors, we conducted monthly transect surveys covering dry and wet seasons in four major habitats on the Waza-Logone flood-plain of Cameroon: dry grasslands, cultivated grasslands, rice fields, and seasonally flooded grasslands resembling natural flood-plain vegetation. We recorded 36 raptor species among 2,533 individuals, dominated by Black Kite Milvus migrans, which comprised 42% of counts. Although richness and diversity were not related to land-use for Palearctic raptors, Afrotropical raptor diversity was higher on the flooded grasslands compared to the newly created cultivated habitats and dry grasslands. The abundance of Afrotropical raptors did not significantly differ across habitats but was lower in rice-fields when Black Kite and Hooded Vulture Necrosyrtes monachus were excluded. Conversely, Palearctic raptor abundance was highest in post-harvest rice fields, demonstrating the importance of the rice fields as foraging habitat for Palearctic raptors. Further transformation of West Africa’s flood-plains is expected, reducing their capacity for Afrotropical raptors, while Palearctic raptors may benefit from expansion of rice-fields, but more research is needed on their vulnerability to pesticide use.