Does illegal hunting skew Serengeti wildlife sex ratios?

Abstract

In this article we show that the population of Serengeti Masai giraffes Giraffa camelopardalis tippelskirchi is extremely female biased, particularly among newborns. Our results suggest that this might be a response to heavy illegal hunting and the continuous disturbance such activities cause on giraffes, as sex ratios were more female skewed in all age groups in areas with high risk of illegal hunting. Giraffes were also more vigilant and fled at longer distances in such areas. Such female skewed sex ratios have also been found in other Serengeti species such as the ostrich Struthio camelus, the impala Aepycerus melampus and the wildebeest Connochaetus taurinus. In all studies, the sex ratio was more female skewed in areas in which illegal hunting is common. We found that sex ratio in giraffe calves, particularly in areas with high risk of illegal hunting, were more female skewed than in subadults or adults, indicating a female biased sex ratio at birth. If wildlife species react to a constant human disturbance by conceiving female offspring, this might cause serious conservation challenges. Conservation managers must anyway take this into account when developing future hunting regimes, not only for giraffes but also for other ungulate species under constant stress. We discuss various hypotheses aiming at explaining the female biased sex ratio in giraffes. However, further studies are needed to disentangle the causes of the skewed sex ratio observed in our study.

The bushmeat trade in African savannas: Impacts, drivers, and possible solutions

“…Within protected areas, bushmeat hunting is more prevalent close to the borders and near human settlements (Muchaal and Ngandjui, 1999;Hofer et al, 2000;Wato et al, 2006;Marealle et al, 2010). Greater distances mean increased time, effort and costs for hunters to find wildlife and transport meat, and higher risk of apprehension (Hofer et al, 2000).…”

“…Lack of research focus has perhaps reflected a misconception that bushmeat hunting in savannas is typically a low impact, subsistence phenomenon (Barnett, 2000;Lindsey et al, 2011a). Literature on the bushmeat trade in savannas is limited to a review of the bushmeat trade in southern and East Africa (Barnett, 2000), and sporadic studies in Serengeti National Park (Hofer et al, 2000;Hofer et al, 2000;Loibooki et al, 2002;Marealle et al, 2010), other sites in Tanzania (Nielsen, 2006;Wilfred and MacColl, 2010), Mozambique (Fusari and Carpaneto, 2006;Lindsey and Bento, 2012), Zimbabwe (Gandiwa et al 2012;Lindsey et al 2011 a,b) and Zambia (Lewis and Phiri, 1998;Lewis, 2005;Brown, 2007;Lewis et al, 2011;Becker et al, 2012). While these studies demonstrate significant negative ecological impacts, the drivers, impacts and interventions needed to address the bushmeat trade in savannas are not well understood.…”

Brain size and the risk of getting shot

“…Hunting may not cause random mortality, but rather result in bias with respect to sex, age and other factors [2,3]. Selection due to hunting is likely to have significant impact on the life history of hunted species of animals [4,5]. In fisheries, selective fishing of large specimens has resulted in reductions in size with consequences for age at first reproduction, clutch size and other life-history traits (e.g.…”

RETRACTED: Population and Trophy Quality Trends of Three Gregarious Herbivores in an Insulated Semi-Arid Savanna Ecosystem (Cawston Ranch, Zimbabwe), 1997–2014

“…Topdown processes such as predation affect the dynamics and persistence of wild herbivores [2,3]. However, 'human predation' through trophy hunting [8][9][10] and illegal off-takes [11,12] is becoming a more important determinant of wildlife population dynamics in most African savanna ecosystems.…”