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Water depth, vegetation height and water edge distance are critical in nest-site selection for Grey Crowned Crane at Lake Ol' Bolossat, Kenya
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  • Wanyoike Wamiti,
  • Nathan Gichuki,
  • Dorcas Sigana,
  • Peter Njoroge,
  • Kerryn Morrison,
  • George Ndung'u,
  • Juan Rubalcaba
Wanyoike Wamiti
National Museums of Kenya
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Nathan Gichuki
University of Nairobi
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Dorcas Sigana
University of Nairobi
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Peter Njoroge
National Museums of Kenya
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Kerryn Morrison
Endangered Wildlife Trust
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George Ndung'u
Crane Conservation Volunteers
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Juan Rubalcaba
University of Montana Missoula
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Abstract

Grey Crowned Crane Balearica regulorum is described as an icon of Africa’s wetlands and grasslands and is listed as Endangered on the IUCN Red List of Threatened species. Efforts towards its conservation actions are nonetheless hindered by among others, lack of knowledge on factors influencing breeding productivity such as nest-site selection. Factors influencing the probability of nest-site selection were investigated at Lake Ol’ Bolossat, a 43.3 km2 wetland located in the central Kenya highlands as a breeding resident. The number and distribution pattern of breeding pairs was also determined. A total of 123 breeding pairs were recorded, 103 in the lake and 20 in the surveyed satellite wetlands thus providing the largest database of breeding Grey Crowned Cranes reported in Kenya to date. Mean breeding pair density for the lake’s marshes was 6.50±0.84 (SE) pairs/km2 with a mean distance between nests of 302.53±17.02 (SE) m. Generalized Linear Models were used to select the most important environmental variables explaining nest-sites selection. The model selection algorithm yielded a subset of 8 best models, where the most important predictor variables (i.e. those with ΔAICc <2) were determined as water depth (preferred above 50 cm), vegetation height (above 60-90 cm) and distance from the water edge (ca.100 m). Water depth and vegetation height had positive effects on nesting probability while the distance to water edge exhibits quadratic tendency. These findings provide key insight into Grey Crowned Crane nesting ecology and a basis for breeding habitat modification and management. This study underscores the importance of Lake Ol’ Bolossat as a critical breeding site and its significant role in the species’ population recovery and survival. The lake should consequently be re-gazetted as a National Park to ensure effective and sustainable control of anthropogenic activities in and around the lake in favour of Grey Crowned Crane.