Kruger Lion Spatial Capture-Recapture Survey
To obtain reliable estimates of lion density, abundance, sex ratio and spatial distribution in the northern and central part of Kruger National Park, the Endangered Wildlife Trust (EWT) in collaboration with SANParks has performed spatial capture-recapture surveys in 2023 and 2024. My role was an assistant in the 2023 survey, and co-lead in the 2024 surveys.
Why?
African lion populations, like many large mammal populations, have declined massively over the past decades. They are currently classified as 'Vulnerable' by the IUCN Red List for Threatened Species. They now roam in human-managed National Parks and Protected Areas or roam freely in low numbers. Both managed and free-roaming, big and small, protected and unprotected populations need to be monitored in order to ensure the persistence of this species. Previous worldwide population estimations have been based on assumptions, and may not reflect the true situation. Therefore, it's important to gain a more realistic picture of their status across Africa. Not only will that provide a scientific base for adequate management strategies; but as many lions live close to people and sometimes pose a risk to their safety and well-being, keeping locals informed about their whereabouts and pro-actively intervening during conflicts is a great way to mediate human-wildlife conflict.
In Kruger National Park, the last lion survey dates back to 2015; therefore it is time for a current and robust estimation!
How?
There are two main components to this methodology: how many lions we find and where, and the amount of effort we put in finding them.
Finding lions
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To find the lions, we perform search encounters: we drive all the roads in the area to see if the lions are there. Although we have to survey all the roads, we often focus on areas that we think lions will be in (close to water and prey), or we are tipped off by rangers or tourists. Once we find lions, we take identification pictures, and we note how many individuals there are and where exactly we found them. In the 2023 survey, we also used camera traps placed throughout the research area to increase our chances of identifying lions.
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Identifying lions
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Lions are hard to identify. They do not have spots like leopards or African wild dogs, and individuals of the same age and sex are often very much alike. The only characteristic that remains constant throughout a lion's life, is the top row of its whisker spot pattern (see pictures of three different females below). Pretty complicated to get a good view of them! That's why we can only identify individuals that are fairly close to us, so that our camera can capture a good shot of their whisker spots. Twigs or grass sometimes obstruct our vision, and lions after a kill are very hard to identify due to all the blood covering the whisker spots. Both the right and left sides of the lion's face have a distinct whisker spot pattern, so it's important to photograph both sides. When using camera traps, we place two camera traps facing each other (but slightly askew so that the flashes don't cancel each other out) to obtain the right and left side of the lion. When we have identified a lion, we either count it as a capture when seen for the first time, and add it to the catalog of the pride. When we've seen the individual before (its already in our catalog), we classify it as a recapture. Therefore, we always know exactly which lions we've encountered, and there are no double counts.
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Although we base the identification solely on the whisker spots, some features help us confirm certain cases. However, caution must be taken when using these additional features, as they can vary greatly over the course of days, weeks or months. Among these additional features are scars, overall size of the individual, mane size, ears, and nose color. Based on the latter, you can estimate a lion's age: young lions have a pink nose, and black spots appear as they grow older. A very dark nose reflects old age! In following pictures, the lion on the left has still quite a bit of pink left, while the lion on the right has a pretty dark nose, and is therefore a much older individual.
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Recording our search efforts
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When we leave camp, we always turn on our Cybertracker app, to record all of our routes. Furthermore, when we encounter lions, we record the amount and the demographics (sex, age). The location is automatically recorded with that information. This information is used to make maps of our driven routes, the amount of kilometers we've driven, and the amount of lions we were able to identify.
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Estimating the number of lions in the area
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This part gets a bit complicated! By combining our counts of individually-identified lions with our search effort, detection probabilities for male and female lions in the area are calculated. Bayesian spatially-explicit capture-recapture models are used to estimate key state variables based on our unstructured spatial sampling. Different models are run, and the winning model (the model that explains the data the best) is used to estimate the total amount of lions in all sections, and therefore in the whole study area. Based on our lion encounters, we also get an idea of the current sex ratio among the different prides, along with other demographical information. Further modeling can be used to investigate other informative processes such as resource selection.
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Marnus Roodbol
Marnus Roodbol
Alison Govaerts
Alison Govaerts
Linda Smit
Linda Smit
Alison Govaerts
Alison Govaerts
Trying to get the best angle for the identification pictures.
Setting up camera traps and preventing any grass to trigger or blurr the picture. Shot taken by the second camera trap opposed to the one seen in the picture.