Detection function, cluster size, density, and population size of Black Crowned Crane Balearica pavonina ceciliae in the upper Blue Nile River, Lake Tana area

Abstract

The aim of the study was to investigate the abundance, density and cluster size of Black Crowned Cranes. Seventy four and 56 transects were examined in 14,764 ha of land in 2015 (wet season) and 2016 (dry season), respectively. Multiple Covariate Distance Sampling model was employed. The encounter rate, detection probability, expected cluster size and density were parameters for estimation. Hazard rate key (σ=0.3), detection function g(x)=1-exp[-(x/σ) ^(-β)], x≤w was selected for analysis. Cluster analysis based on exact sizes was computed by regression of log(s(i)) on g(x(i)). The minimum Akaike Information Criterion was chosen during estimator selection. The result showed that the cluster size of cranes during the wet season in wetland and farmland habitats regression estimate were Cwi=0.73+0.16*xi; and Cfi=0.52+-0.21*xi, respectively. Similarly, in 2016, the regression estimate of wetland and farmland were Cwi=0.16+0.56*xi and Cfi=0.20+-0.34*xi, respectively. During the wet season in 2015, in the wetland habitat, the crane density was estimated 0.21768±0.82 per hectare, and the total population (N) was estimated to be 1472±554.62. Whereas in the farmland, crane density was estimated 0.79921 E-01±0.13370E-01 per hectare, and the total population (N) was estimated to be 639. The total density and abundance of Black Crowned Cranes during the wet season in 2015 was estimated. The wet season pooled density estimate was 14.304 cranes per 100 hectares with (% CV = 26.75, df = 50.2, 95%CI= 0.84355E-01=CI = 0.24254) and the population size was estimated to be 2112 cranes with (% CV = 26.75, df = 50.2, 95%CI = 1245=CI = 3581). During the dry season, in 2016, the crane density was estimated 0.3625±0.6958E-01 per hectare, and the total population (N) was estimated to be 2452±470.65. In the farmland, the cranes density was estimated 0.13904±0.14809E-01 per hectare, and the total population (N) was estimated to be 1112±118.44. The dry season pooled density estimate was 24.142 cranes per 100 hectares with (%CV=13.62, df = 164.02, 95%CI = 0.18473=CI= 0.31550) and the population was estimated to be 3564 cranes with (%CV=13.62, df = 164.02, 95%CI = 2727=CI = 4658). In conclusion, the cluster size of cranes in wetland and farmland habitat during the dry season showed that the species consisted of a small number of cranes per family. However, the wetland habitat was more suitable than the farmland in consisting of larger cluster size and overall population of cranes. Wetland degradation is a threat for cranes.