How people, food affect giraffe movement
Giraffes reduce their movements when human pressures are highest and when forage resources are richest.This according to a study published in Proceedings of the Royal Society by an international research team led by Dr Michael Butler Brown, an ecologist with the Giraffe Conservation Foundation (GCF) and Smithsonian’s National Zoo and Conservation Biology Institute.
When resources and human pressures are less predictable in space and time, giraffes must cover much more ground. This finding has conservation implications in a rapidly developing world.
Giraffes live in incredibly diverse environments across 21 African countries. These environments span impressive ecological gradients: from the hyper-arid deserts of northwest Namibia to the lush savannahs along Uganda’s Nile River. They also vary significantly in the level of human impact: from the semi-arid pastoral landscapes of Niger’s Sahel to protected private reserves of Southern Africa.
Brown and 24 colleagues tested how these ecological and human impact gradients affect giraffe space use and movement behaviour across their range in Africa.
Brown and colleagues collected GPS tracking data from 148 animals of all four giraffe species from across ten countries to understand how giraffes change space use patterns in response to human pressures and the availability/predictability of forage resources.
To achieve this goal, the team designed and applied different types of GPS tracking units specifically for giraffes since traditional GPS collars do not work well on their long necks. These devices collected millions of locational fixes and relayed them through satellite networks so the researchers could track giraffe locations across some of the continent’s remotest environments. This is the largest movement study ever conducted on giraffes.
Home range
Overall, giraffes cover impressively large areas, with an average home range size of 360 km² and average daily movements of over 14 km, although these space use patterns changed based on the vegetation availability and intensity of human presence.
“We found that in areas with consistently high availability of woody vegetation, giraffes don’t cover as much ground since they generally have most of the resources they need nearby. Similarly, giraffes tend to move less in places with a consistently intense human footprint, likely because of anthropogenic barriers restricting their ability to move,” Brown says.
“Where the story gets more interesting is in the more heterogeneous systems where giraffes cover more ground as they navigate more patchy environments.”
Because giraffes live across diverse environments with measurably different conditions, they are an ideal study species to test these ideas. To do so, Brown and colleagues used continental-scale environmental datasets derived from satellite imagery, linking the giraffe locations to the exact conditions in space and time.
Since the work drew from data collected throughout Africa through different high-resolution GPS devices, it required applications of novel statistical techniques so that results were directly comparable. Using continuous-time movement models (CTMM) and mixed effects meta regressions, the team developed and applied statistical methods that effectively allow for a comparison of giraffe space use metrics across various sites and tracking technologies.
These newly applied methods can be used much more broadly in other movement ecology studies to make robust comparisons of animal movement behaviours under diverse conditions.
Implications
Understanding how giraffes respond to changes in environmental conditions is critical for informing their conservation. Recent estimates suggest only 117 000 giraffe are remaining in the wild of Africa, and many of their populations are found in rapidly changing environments.
“As human populations continue to grow and climate change renders the predictability of resources more uncertain, understanding how giraffes will spatially respond to these changes is critical to ensuring that conservation strategies effectively account for different movement strategies,” says Dr Julian Fennessy, the co-founder and director of conservation of the GCF.
“Understanding giraffe spatial needs helps us to guide important conservation efforts in new and reclaimed environments, e.g. for conservation translocations which are increasingly used as a tool to re-establish giraffe populations across their range in Africa.”