Movements and source–sink dynamics of a Masai giraffe metapopulation

A giraffe population can look healthy while depending on arrivals from elsewhere. Animals moving across a landscape can conceal differences between places that sustain giraffes and places where local losses are harder to replace. A headcount alone cannot reveal which areas are supporting the wider population.

Derek Lee and Douglas Bolger followed individually recognisable female giraffes across five management areas in Tanzania's Tarangire region. Eighteen photographic surveys from 2012 to 2014 produced histories for 1,094 females of different ages. The researchers combined estimates of survival, reproduction and movement to assess each area's contribution to the connected population, rather than judging it only by the number of giraffes present.

The two national parks and Manyara Ranch Conservancy contributed as population sources, while two game-controlled areas functioned as sinks. Tarangire National Park made the largest overall contribution; the ranch contributed especially strongly per animal. Movements were uncommon but connected all five areas. Some observed crossings could have been repeated use of neighbouring land rather than permanent relocation, and the comparison did not isolate the causes of differences in survival. Even so, it identified a conservation priority that counts can overlook: protecting adult females in productive areas benefits giraffes beyond those areas' boundaries.