Introduction
The global lion (Panthera leo) population is thought to have declined by about 75% (Loveridge et al. 2022) over the last five decades, with more than 43% of the decline occurring since the early 1990s (Bauer et al. 2015). Several factors have accounted for this decline, including land use change (Riggio et al. 2013), declines in prey species abundance (Elliot & Gopalaswamy 2017, Lindsey et al. 2017), illegal killing through poaching and retaliation (Visser et al. 2009, Lindsey et al. 2017) and poorly regulated hunting (Loveridge et al. 2007, Kissui 2008, Packer et al. 2011). This decline in abundance varies regionally, with populations smaller and more fragmented in West Africa and India than in eastern and southern Africa (Bauer & Van Der Merwe 2004, Tumenta et al. 2010).
Declines in lion populations and associated habitat have elevated the importance of developing population survey techniques to facilitate conservation efforts (Riggio et al. 2013). Many lion survey techniques have been used, including track surveys (Stander 1998, Midlane et al. 2014, Crosmary et al. 2018), call-in surveys (Ogutu & Dublin 1998, Jacobson et al. 2013), distance sampling (Durant et al. 2011), mark–resight (Mills et al. 1978, Ogutu et al. 2006), aerial surveys (Talbot & Stewart 1964), secondary information or expert opinion (Chardonnet 2002, Bauer & Van Der Merwe 2004, Riggio et al. 2013), total counts of identified individuals (Tumenta et al. 2010, Becker et al. 2013) and DNA-based estimates (Tende et al. 2010). As techniques and associated study designs vary markedly, the resulting estimates and estimates of precision have similarly varied (Chećko 2011, Elliot & Gopalaswamy 2017). For example, many total count studies do not report search effort, which can further limit our understanding of estimated precision and cost-effectiveness. Long-term monitoring studies (e.g. Funston 2011, Cusack et al. 2015) may also violate population closure assumptions (Stander 1991). Additionally, methods that use advanced tracking devices [e.g. GPS collars (Loveridge et al. 2016)] may be cost prohibitive. Although lion-survey techniques have been combined or used interchangeably, a comprehensive assessment of their utility is lacking.
We reviewed lion population estimate studies to 1) provide a comprehensive list, means of data collection and analysis of field methods used; 2) characterize their accuracy, precision and cost-effectiveness and 3) assess the suitability of techniques used to achieve primary study objectives.