Population size and breeding ecology of Yellow-billed Duck (Anas undulata, Dubois 1839) in Chelekleka wetland, Ethiopia

Yellow-billed Duck (Anas undulata) is a monomorphic African endemic dabbling duck protected by the Conservation of African-Eurasian Migratory Water birds Agreement. This study was conducted to investigate the population size and breeding ecology of Yellow-billed Duck in Chelekleka wetland, Ethiopia from November 2020 to October 2021. Census was conducted during early morning from 6:30 - 10:00 hrs and late afternoon from 15:30 - 18:00 hrs twice per week when the birds are active. Direct observations as well as nest and egg morphometry measurements were conducted to collect data on breeding ecology of Yellow-billed Ducks. During the study period, eight active nests were identified and followed. Data were analysed using R version 4.2 software. A maximum of 315 individuals of Yellow-billed Ducks were counted, with a significantly high population size during dry season compared to wet season (Z = - 10.85, df = 63, p < 0.001). The female Yellow-billed Duck built a nest made up of herbs, defoliated leaves, dried grasses and thin twigs. The nest is circular shaped with a 26 - 32 cm in diameter and 7 - 11 cm in height. They laid eggs that are light brownish. Clutch size ranged from 5 - 8 eggs. The mean egg length, breadth and weight were 45.38 ± 1.65 mm, 39.17 ± 0.58 mm, and 45.4 ± 1.7 gm, respectively (n = 21). The average incubation period per nest was 19 ± 0.82 days (n = 4) with a high hatching success (98.1 %; n = 53). Supporting a considerable number of Yellow-billed Ducks, Chelekleka wetland is ecologically important for breeding and other related ecological requirements of the species. However, anthropogenic factors such as; burning of nesting bushes, wetland degradation, and agricultural expansions are highly threatened their survival. Therefore, sustainable conservation intervention is needed to minimize the threats on the species and its habitat.