Browsing by Author "Ottosson, Ulf"
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Item Density and diversity of birds in the wetlands of Yankari Game Reserve, Bauchi, Nigeria(Journal of Wetlands Ecology, 2011-12-30) Omotoriogun, Taiwo C.; Onoja, Joseph Daniel; Tende, Talatu; Manu, Shiiwua; Ottosson, UlfThe biological, chemical, and physical operations and attributes of wetlands are vital in facilitating food resources, water, and shelter, which many terrestrial bird and waterbird species rely on for their daily requirments. Wetlands in Yankari Game Reserve, Nigeria are key stone ecosystem that provides a stopover, breeding and/or foraging platform for migratory and resident birds. This study determined the density and diversity of birds in the wetlands of Yankari Game Reserve. Ten wetlands within the reserve were identified and surveyed. The sizes (kilometer square) and isolation distances (kilometer) of the wetlands were measured (using GPS and Map Source) to determine their effects on bird density and diversity. Point count survey method was used to count birds. One hundred and twenty three species of birds belonging to 51 families were recorded in the wetlands. Significant patterns in the densities of birds were observed across the wetlands (Kruskal-Wallis H, X2=167.116, P=0.001) and also sizes of wetlands (Wilcoxon test: Z= -2.803, P=0.005). There was differences in mean number of birds in survey time (Kruskal-Wallis, X2=15.784, P=0.045). Evenings were probably most preferred in bird-wetland utilization.Item Large mammals and wetland utilisation: A case study in Yankari Game Reserve, Nigeria(Wiley, 2019-04-28) Omotoriogun, Taiwo C.; Tende, Talatu; Adeiza, Zainab O.; Onoja, Joseph D.; Karau, Shomboro; Mwansat, Georgina S.; Ottosson, Ulf; Manu, Shiiwua A.Item Sperm competition in tropical versus temperate zone birds(Royal Society Publishing, 2012-11-21) Albrecht, Toma´sˇ; Kleven, Oddmund; Kreisinger, Jakub; Laskemoen, Terje; Omotoriogun, Taiwo C.; Ottosson, Ulf; Reif, Jirˇı´; Sedla´cˇek, Ondrˇej; Horˇa´k, David; Robertson, Raleigh J.; Lifjeld, Jan T.Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CVbm) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis.