Effects of grassland fragmentation and precipitation on secretarybird Sagittarius serpentarius reproduction in the Serengeti ecosystem

Le résumé fourni par la source

Accurate demographic data are essential for understanding population dynamics and developing effective conservation strategies for threatened raptor species. This study provides the first quantitative assessment of how grassland fragmentation at landscape scale, driven by woody plant encroachment, and interannual variation in precipitation affect the secretarybird Sagittarius serpentarius reproduction within the Serengeti ecosystem in Tanzania. Through nest density estimation models based on nest survival and detection probabilities, and generalized additive mixed models, we estimated nesting success and productivity across three habitat types with different grassland fragmentation levels and rainfall regimes during the 2023 and 2024 breeding seasons. Nest density was highest in habitats with moderate to low fragmentation (50–< 90% grassland cover: 7.6 nests 100 km −2 ), lower in highly fragmented habitats (< 50% grassland cover), and lowest in minimally fragmented ones (> 90% grassland cover). Nesting success increased significantly with grassland cover, from 18.9% in highly fragmented habitats – possibly due to greater influence of edge effects – to 71% in minimally fragmented ones. Productivity was lowest in highly fragmented habitats (0.8 successful nests 100 km −2 ), highest in moderately to low fragmented ones (2.5), and intermediate in minimally fragmented habitats (1.7). Wet‐season rainfall emerged as dominant driver of nest abundance across all habitat types. Substantially higher precipitation in 2024 than 2023 correlated with a nearly three times higher nest abundance in 2024 compared to 2023, positively influencing productivity (2.2 versus 0.8 successful nests 100 km −2 ). Additionally, lower long‐term dry‐season rainfall negatively affected nesting success. These findings highlight the secretarybird vulnerability to habitat and climate change, which may disrupt predator–prey dynamics and reduce nesting site quality and the number of breeding attempts. Conservation efforts in fragmented habitats should prioritize limiting the effects of woody plant encroachment and actively protecting nests to mitigate predation risks, thereby enhancing productivity and sustaining steady populations of this African savannah raptor.

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