Male-Biased Partial Migration in a Giraffe Population

Some giraffes migrate while their neighbours stay behind. In Uganda’s Murchison Falls National Park, animals living in the same landscape used three different strategies: remaining in one of two contrasting habitats, or moving between them with the seasons. The seasonal travellers were not simply wandering farther within a permanent home range.

Michael Brown and Douglas Bolger combined GPS tracking with photographic records of 1,453 individually recognised giraffes collected over three years. Eight female giraffes had tracking records long enough for detailed seasonal analysis. Repeated photographs supplied the broader comparison between males and females, while vegetation surveys and satellite observations described how the two habitats differed and changed through the year.

Four tracked females migrated between ranges roughly 13–30 kilometres apart; four remained resident. Migrants shifted from acacia-rich savanna towards broadleaf savanna during the dry season and returned towards their wet-season range when rains resumed. Across the photographic dataset, males had higher probabilities of seasonal moves than females. Food availability, body size and mating opportunities offered possible explanations, but the study did not establish which drove the difference. Its clear finding was that migration belongs to particular giraffes, not necessarily the whole population: protecting one resident area would miss the seasonal needs of its travelling neighbours.