The goal of Wild Nature is to understand where giraffes and other ungulates are doing well and where they are not, and why, and to protect and connect the places most important for wildlife and nomadic Maasai people. The ecological resiliency of a large landscape like the Tarangire Ecosystem is reinforced when all the parts are conserved.
Wild Nature Institute is conducting the world’s largest individual-based study of Maasai giraffes (Giraffa camelopardalis tippelskirchii). We use pattern-recognition software to track more than 3,000 individuals in a 4,000-square kilometer area to understand births, deaths, and movements in the fragmented Tarangire Ecosystem. Our results inform conservation and land management, and help ensure a future for giraffes and Maasai people. Here is a summary of what we’ve discovered about wildlife in Tarangire that will help conserve these magnificent mega-herbivores throughout Tanzania.
Precision, accuracy, and costs of survey methods for giraffe Giraffa camelopardalis was one of our first publications from the project. We estimated giraffe density and abundance in the Tarangire Ecosystem in northern Tanzania using two ground survey methods—distance sampling and capture-mark-recapture—and compared our ground-based estimates with those from the most recent aerial survey. We found aerial survey estimates were biased low, while ground-based surveys were more precise and cost less. However, aerial surveys are useful over large regions of Tanzania and thus can provide landscape-scale population estimates. We computed correction factors to improve the accuracy of aerial surveys and suggested ways to further improve aerial survey methods.
Our two papers about Giraffe Skin Disease (GSD), The occurrence and prevalence of giraffe skin disease in protected areas of northern Tanzania, and Soil correlates and mortality from giraffe skin disease in Tanzania described the disorder in the Journal of Wildlife Diseases. We documented that GSD prevalence was best explained by soil fertility, with less disease prevalence on more fertile soils. We found no mortality effect of GSD on adult giraffe in Tarangire National Park. Based on our findings, GSD is unlikely to warrant immediate veterinary intervention, but continued monitoring is recommended to ensure early detection if GSD-afflicted animals begin to show signs of increased mortality or other adverse effects.
In Spatial variation in giraffe demography: a test of 2 paradigms, we examined whether spatial variation in demography of a tropical mega-herbivore (the giraffe) followed the “temporal paradigm” or the “adult survival paradigm” of ungulate population dynamics that were formed from temperate-zone studies. We quantified how giraffe demographic rates of survival and reproduction varied across space at regional (northern Tanzania) and continental (Africa-wide) scales. Spatial variability of demographic rates at the continental scale supported the temporal paradigm of low variability in adult survival and more highly variable reproduction and calf survival. In contrast, at the regional scale, adult female survival had higher spatial variation, which supported the adult survival paradigm. At both scales, variation in adult female survival made the greatest contribution to variation in local population growth rates. We also found human-caused reductions in adult female giraffe survival are the most likely reasons of population declines.
In Giraffe demography and population ecology, we summarized current knowledge of demography and population ecology of giraffes and provided a framework for using population models when developing and evaluating conservation and management efforts for giraffes (or other large herbivore species).
In Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes, we utilized our data about a large-mammal predator–prey savanna food web to evaluate support for 2 hypotheses relating to the indirect effects of “apparent competition” and “apparent mutualism.” We examined how the presence of migratory herds of wildebeests (Connochaetes taurinus) and zebras (Equus quagga) affected survival of resident giraffe calves, as mediated by their shared predator, African lions (Panthera leo). African lions are generalist predators whose primary, preferred prey are wildebeests and zebras, but lion predation on secondary prey such as giraffes may change according to the relative abundance of the primary prey species. We found that local lion predation pressure on giraffes was reduced by local density of wildebeests and zebras, making giraffe neonatal and calf survival probabilities higher when the migratory herds were present. This supported the apparent mutualism hypothesis.
Natural predation had a significant effect on giraffe calf and neonate survival, and could significantly affect giraffe population dynamics, thus if wildebeest and zebra populations in this ecosystem continue to decline as a result of increasingly disrupted migrations and poaching, then giraffe calves will face increased predation pressure as the predator–prey ratio increases. Our results suggest that the widespread population declines observed in many migratory systems are likely to trigger demographic impacts in other species due to indirect effects like those shown here.
We were proud to contribute to the IUCN Red List Assessment for giraffes, which reclassified giraffes as Vulnerable due to an observed population decline of 36–40% over three generations (30 years, 1985–2015). The factors causing this decline (direct killing and habitat loss) have not ceased throughout the species’ range. The best available estimates indicate a total population in 1985 of 151,702–163,452 giraffes (106,191–114,416 mature individuals), and in 2015 a total population of 97,562 giraffes (68,293 mature individuals). Some giraffe populations are stable or increasing, while others are declining, and each population is subject to pressure by threats specific to their local country or region. The populations of giraffes are scattered and fragmented with different growth trajectories and threats, but the species trend reveals an overall large decline in numbers across its range in Africa.
We also documented for the first time that Season of birth affects juvenile survival of giraffe. Variation in timing of reproduction and subsequent juvenile survival often plays an important role in population dynamics of ungulates in temperate and boreal regions. Tropical ungulates often give birth year round, but survival effects of birth season for tropical ungulate species were previously unknown. We found significant differences in juvenile survival according to season of birth, with calves born during the dry season experiencing the highest survival probability. Phenological match (matching birth season with vegetation growth) may explain the juvenile survival advantage to offspring born during the dry season from 1) greater accumulated maternal energy reserves in mothers who conceived in the long rainy season, 2) high-protein browse in the late dry-early short rainy seasons supplementing maternal and calf resources, 3) reduced predation due to decreased stalking cover, or some combination of these. Asynchrony is believed to be the ancestral state of all ungulates, and this investigation illustrated how seasonal variation in vegetation can affect juvenile survival and may have played a role in the evolution of synchronous births.
We also contributed to a lively discussion about How many species of giraffe are there? Giraffes are presently classified as one species, with nine subspecies. A paper in Current Biology presented DNA data and a taxonomy with four species of giraffe. The present consensus of one species divided into nine subspecies had previously been questioned several times over the past few decades. We presented the various taxonomic schemes and offered that the fundamental reason for different taxonomic interpretations is that they are based upon different datasets that adopt different statistical techniques and follow different criteria. These different taxonomies create a basis for future taxonomy discussions and conservation efforts.
Movements and source–sink dynamics of a Masai giraffe metapopulation provided a regional metapopulation analysis of the Tarangire ecosystem to inform conservation management for Masai giraffes in five subpopulations defined by land management designations. We assessed the source–sink structure of the study population, and we created a matrix metapopulation model to examine how variation in demographic components of survival, reproduction, and movement affected metapopulation growth rate. Movement data indicated no subpopulation was completely isolated, but movement probabilities varied among subpopulations. Source–sink statistics and flow of individuals indicated three subpopulations were sources, while two subpopulations were sinks. We found areas with higher wildlife protection efforts and fewer human impacts were sources, and less-protected areas were identified as sinks. Our results highlight the importance of identifying source–sink dynamics among subpopulations for effective conservation planning and emphasize how protected areas can play an important role in sustaining metapopulations.
The Tarangire migration is one of only three long distance migrations of wildebeest (Connochaetes taurinus) remaining in Africa. The wildebeest population in the Tarangire Ecosystem of northern Tanzania decreased from an estimated 40,000 animals in 1988 to approximately 7000 today. We used A multi-method approach to delineate and validate migration corridors for wildebeest to inform rangeland conservation and land use planning. Conserving landscape-scale migratory habitat for wildebeest will also protect important rangelands for Maasai pastoralists and their livestock.
Two papers explored the Ecological effectiveness of community-based Wildlife Management Areas (WMAs). In Tanzania, community-based natural resource management (CBNRM) of wildlife occurs through WMAs. The WMAs consist of multiple villages designating land and managing it for wildlife conservation in return for a portion of subsequent tourism revenues. In Randilen WMA, we documented significantly higher densities of resident wildlife (giraffes and dik-diks) and lower densities of cattle in the WMA, relative to the control site, indicating short-term ecological success. In a paper about to be published using data from Burunge WMA, we found greater densities of wildlife and lower densities of livestock inside the WMA compared with outside. After management changes, we documented significantly higher densities of several wild ungulate species and lower densities of domestic ungulates in the WMA. These combined results indicate the ecological effectiveness of Randilen and Burunge WMAs and provide evidence that CBNRM can have positive effects on wildlife populations, particularly when support to grassroots law enforcement is provided.
We are currently collecting more data and conducting lots more analyses that will investigate juvenile dispersal, giraffe social structure, how sociality affects survival and reproduction, and other interesting topics. Learn more about our work at www.WildNatureInstitute.org .
D.E. Lee & M.L. Bond. 2016. "Precision, accuracy, and costs of survey methods for giraffe Giraffa camelopardalis." Journal of Mammalogy 79:940-948.
D.E. Lee, B.M. Kissui, Y.A. Kiwango & M.L. Bond. 2016. "Migratory herds of wildebeest and zebra indirectly affect juvenile survival of giraffes." Ecology and Evolution DOI: 10.1002/ece3.2561.
D.E. Lee & M.K.L. Strauss. 2016. "Giraffe demography and population ecology." Reference Module in Earth Sciences and Environmental Studies. DOI: 10.1016/B978-0-12-409548-9.09721-9.
D.E. Lee, M.L. Bond, B.M. Kissui, Y.A. Kiwango & D.T. Bolger. 2016. "Spatial variation in giraffe demography: a test of 2 paradigms." Journal of Mammalogy 79:1015-1025.
D.E. Lee & M.L. Bond. 2016. "The occurrence and prevalence of giraffe skin disease in protected areas of northern Tanzania." Journal of Wildlife Diseases 52:753-755.
M.L. Bond, M.K.L. Strauss & D.E. Lee. 2016. "Soil correlates and mortality of giraffe skin disease in northern Tanzania." Journal of Wildlife Diseases DOI:10.7589/2016-02-047.
Z. Muller, F. Bercovitch, J. Fennessy, D. Brown, R. Brand, M. Brown, D. Bolger, K. Carter, F. Deacon, J. Doherty, S. Fennessy, A.A. Hussein, D. Lee, A. Marais, M. Strauss, A. Tutchings & T. Wube. 2016. "Giraffa camelopardalis." The IUCN Red List of Threatened Species 2016: e.T9194A51140239.
F.B. Bercovitch, P.S. Berry, A. Dagg, F. Deacon, J.B. Doherty, D.E. Lee, F. Mineur, Z. Muller, R. Ogden, R. Seymour & B. Shorrocks. 2017. "How many species of giraffe are there?" Current Biology 27:R136-R137.
D.E. Lee & D.T. Bolger. 2017. "Movements and source-sink dynamics among subpopulations of giraffe." Population Ecology DOI 10.1007/s10144-017-0580-7.
D.E. Lee, M.L. Bond & D.T. Bolger. 2017. "Season of birth affects juvenile survival of giraffe." Population Ecology 59:45-54 DOI 10.1007/s10144-017-0571-8.
M.L. Bond, C.M. Bradley, C. Kiffner, T.A. Morrison, D.E. Lee. 2017. “A multi-method approach to delineate and validate migratory corridors.” Landscape Ecology 32:1705-1721.
D.E. Lee, M.L. Bond. 2018. “Quantifying the ecological success of a community-based wildlife conservation area in Tanzania.” Journal of Mammalogy 99:459-464.
D.E. Lee. 2018. “Evaluating Conservation Effectiveness in a Tanzanian Community Wildlife Management Area.” Journal of Wildlife Management in press.
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