Using Age to Inform Management and Research
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Managers use population models based on the age structure of a population to help predict how different management scenarios or environmental stressors might affect the future of a species. Population models project a species’ population size based on information about a species’ life history, including conception rate, birth rate, survival of young, age at puberty, territoriality and other behavioural characteristics. The age or life stage of an animal is closely tied to its reproduction, survival, behavior, and other aspects of its ecology that can affect population stability. Thus, an animal’s age in the context of its population can provide valuable information about the future of a single population and, for threatened species like the African lion, even the species as a whole.
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4 month-old cubs in Hwange, Zimbabwe. Photo by WildCRU.
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For this reason, age is an important metrics collected by lion researchers. For example, researchers that collar individual lions must be able to accurately age the lions they study in order to understand lion behaviour in a broader context. Ensuring that lions have the natural resources and the protection that they require at different phases of their lives is critical for ensuring their conservation.
Importance of Aging for Sustainable Hunting
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Lions are the only social big cats in the world. Each pride consists of 4-5 adult lionesses, their dependent cubs, and a temporary coalition of pride males. Pride males play a key role in defending their pride against invading males by forming coalitions of 2-3 males to defend the pride territory through roaring, patrolling, scent marking and aggressively approaching invading males. When new males enter a pride, they often kill cubs (a behavior termed "infanticide") in order to bring lionesses into estrus more quickly so they can produce offspring. Infanticide ensures that the new male will pass on his genes to boost his reproductive fitness, while reducing the fitness of previous pride males.
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A 6-year old male and his pride in Hwange, Zimbabwe. Photo by WildCRU.
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The social nature of lions and common use of infanticide means that lion populations are greatly impacted by the loss of males. For example, when 72% of the adult males studied in Hwange National Park, Zimbabwe were hunted, these pride males were replaced by invading males that caused high rates of infanticide and disrupted population stability (Loveridge et al. 2007). Many of the hunted males were sub-adults less than 4 years old and had few opportunities to reproduce, making their loss especially impactful on the long-term stability of the population.
Because of this, trophy hunting must be managed in a way that reduces infanticide to achieve sustainable lion populations and long-term harvests. Simulation models suggest that sustainable trophy hunting can be accomplished by harvesting only adult males that have raised cubs to independence. (Note that females should never be hunted because their removal consistently leads to population decline). The age of physical and sexual maturation in male lion differs slightly between geographic areas of Africa, with males in East Africa maturing by around 4 years (Whitman et al. 2004) and males in southern Africa maturing by 6-7 years (Loveridge et al. 2007). Reproducing and raising cubs to independence typically requires an additional 1-2 years.
Studies have found that to be sustainable (achieve stable lion populations and maximum harvests), trophy hunting should target lions in East Africa (Tanzania) older than 6 years (Whitman et al. 2004, 2007) and lions in southern Africa older than 8 years. As a general rule, hunting males older than 8 years maximizes both the quantity and the quality of the long-term harvest. The science of aging lions in part grew out of the need for more reliable indicators of age to make trophy hunting sustainable.
Because of this, trophy hunting must be managed in a way that reduces infanticide to achieve sustainable lion populations and long-term harvests. Simulation models suggest that sustainable trophy hunting can be accomplished by harvesting only adult males that have raised cubs to independence. (Note that females should never be hunted because their removal consistently leads to population decline). The age of physical and sexual maturation in male lion differs slightly between geographic areas of Africa, with males in East Africa maturing by around 4 years (Whitman et al. 2004) and males in southern Africa maturing by 6-7 years (Loveridge et al. 2007). Reproducing and raising cubs to independence typically requires an additional 1-2 years.
Studies have found that to be sustainable (achieve stable lion populations and maximum harvests), trophy hunting should target lions in East Africa (Tanzania) older than 6 years (Whitman et al. 2004, 2007) and lions in southern Africa older than 8 years. As a general rule, hunting males older than 8 years maximizes both the quantity and the quality of the long-term harvest. The science of aging lions in part grew out of the need for more reliable indicators of age to make trophy hunting sustainable.
Further Reading
Lion Biology
Aging Lions and Sustainable Trophy Hunting
- Funston, P. J., M. G. L. Mills, P. R. K. Richardson, and A. S. van Jaarsveld. 2003. Reduced dispersal and opportunistic territory acquisition in male lions (Panthera leo). Journal of Zoology 259:131–42. Free!
- Mosser, A., and C. Packer. 2009. Group territoriality and the benefits of sociality in the African lion, Panthera leo. Animal Behaviour 78:359–370.
- Packer, C., D. Scheel, and A. E. Pusey. 1990. Why lions form groups: food is not enough. American Naturalist 136:1–19. Free!
- Pusey, A. E., and C. Packer. 1994. Non-offspring nursing in social carnivores: minimizing the costs. Behavioral Ecology 5:362-374.
Aging Lions and Sustainable Trophy Hunting
- Creel, S., M’soka, J. , Droge, E., Rosenblatt, E.G., Becker, M. S., Matandiko, W., Simpamba, T. In press (coming soon). Assessing the sustainability of African lion trophy hunting, with recommendations for policy. Ecological Applications, DOI: 10.1002/eap.1377.
- Miller, J., Balme, G., Lindsey, P. A., Loveridge, A. J., Becker, M. S. Begg, C., Brink, H., Cotterill, A., Dolrenry, S., Hunt, J. E., Jansson, I., MacDonald, D. W., Mandisodza-Chikerema, R., Packer, C., Rosengren, D., Stratford, K., Trinkel, M., White, P., Winterbach, C., Winterbach, H. E. K., and Funston, P. J. 2016. Aging traits and sustainable trophy hunting of African lions. Biological Conservation 201:160-168. Free!
- Loveridge, A. J., A. W. Searle, F. Murindagomo, and D. W. Macdonald. 2007. The impact of sport-hunting on the population dynamics of an African lion population in a protected area. Biological Conservation 134:548–558.
- Rosenblatt, E., Becker, M. S., Creel, S., Droge, E., Mweetwa, T., Schuette, P. A., Watson, F., Merkle, J., Mwape, H. 2014. Detecting declines of apex carnivores and evaluating their causes: An example with Zambian lions. Biological Conservation 180:176–186. Free!
- White, P. A. , Belant, J. L. 2016. Individual variation in dental characteristics for estimating age of African lions. Wildlife Biology 22: 71–77. Free!
- White, P. A., Ikanda, D. , Ferrante, L., Chardonnet, P., Mesochina, P., Cameriere, R. 2016. Age estimation of African lions Panthera leo by ratio of tooth areas. PLoS ONE. Doi: 10.6084/m9.figshare.3159430. Free!
- Whitman, K. L., Starfield, A. M., Quadling, H. S., and C. Packer. 2004. Sustainable trophy hunting of African lions. Nature 428:175–178. Free!
- Whitman, K. L., Starfield, A. M., Quadling, H., Packer, C. 2007. Modeling the effects of trophy selection and environmental disturbance on a simulated population of African lions. Conservation Biology 21:591–601. Free!