Nest characteristics and morphometry of Black Crowned Cranes Balearica pavonina ceciliae in Lake Tana area wetlands

Abstract

Birds select breeding habitats based on biotic and abiotic environmental factors, resulting in a non-random spatial distribution of nests. This study investigated the onset of nesting, nest location, the relationship between nest height and water depth, nest materials, and the structure and characteristics of Black Crowned Crane nests in the Lake Tana region, Ethiopia. A total of 52 nests were recorded in four wetlands from 2014 to 2015. Nesting activity predominantly took place from September to October. There was a significant difference in the distance from nests to the edge of the wetland (χ² = 24.843, n = 46, df = 3, p < 0.001). However, in all study areas the distance between nests, which indicates the degree of territoriality, did not show any significant difference (χ² = 6.016, n = 34, df = 3,
p = 0.111). In addition, nests were constructed in the wetland where the water depth ranged from 80 to 220 cm. Nest height (H2i) and water depth (WDi ) at nesting sites were highly correlated, and the regression equation (H2i = 13.77 + 1.03WDi) indicated that when the water depth increases, the nest height also increases. The shallowest depth where a nest was constructed was 80 cm. Vegetation type varied, but cranes used Leersia hexandra, Oryza longistaminata, and Cyprus rotundus plants as their selected nesting material. The average vegetation height observed at nests with eggs, measured one metre away from the nest rim, ranged from 20 to 90 cm (44.83 ± 2.397), n = 48. The vegetation height at each study site showed no significant difference (F(3) = 2.527, p = 0.07). The mean nest length,
width, and height from the surface of the water between nests were not significantly different. Nesting density was variable depending on the size of the wetland, water depth, and vegetation type and cover.

Keywords: nest density, nest height, nest measurements, nesting material, water depth