“I tawt I taw a puddy tat!": Extinction and uncertain sightings of the Barbary lion

As species become rare and approach extinction, purported sightings can be controversial, especially when scarce management resources are at stake. We report a Bayesian model where we consider the probability that each individual sighting is valid. Obtaining these probabilities clearly requires a strict framework to ensure that they are as representative as possible. We used a process, which has proven to provide accurate estimates from a group of experts, to obtain probabilities for the validation of 35 sightings of the Barbary lion. We considered the scenario where experts are simply asked whether a sighting was valid, as well as when we asked them to score the sighting based on distinguishablity, observer competence, and verifiability. We find that asking experts to provide scores for these three aspects resulted in each sighting being considered more individually. Additionally, since the heavy reliance on the choice of prior can often be the downfall of Bayesian methods, we use an informed prior which changes with time.