Socially Defined Subpopulations Reveal Demographic Variation in a Giraffe Metapopulation

Giraffes can share ground without sharing the same reproductive success. Distinct female communities whose ranges overlapped still differed in the numbers of calves recorded per female. Drawing boundaries only around parks or habitats could therefore miss divisions that matter to the animals themselves.

Monica Bond, Barbara König and colleagues used repeated photographs from Tanzania's Tarangire ecosystem to identify ten social communities. Their 2011–2016 observations supplied records for 684 adult females and 744 calves for reproductive estimates, with slightly smaller samples for survival. Building on earlier evidence of overlapping communities, they compared calf-to-female ratios and survival with vegetation, soils, human proximity, giraffe density and the strength of female associations.

Adult female survival showed no clear difference among communities, but calf survival and calf-to-female ratios did. More dense bushland was associated with lower calf survival; volcanic soils and proximity to settlements were associated with more calves per female. These correlations do not establish whether food, predators or other factors caused the differences. Female relationship-strength measures did not explain them either. The contribution is a finer view of a population: giraffes occupying overlapping land can belong to distinct communities with different prospects for producing and retaining young.