Kalahari skinks eavesdrop on sociable weavers to manage predation by pygmy falcons

A new study led by researchers at the FitzPatrick Institute of African Ornithology, University of Cape Town that investigated whether Kalahari tree skinks are able to eavesdrop and cue on sociable weavers to avoid predation, was recently published in the journal Behavioral Ecology  https://doi.org/10.1093/beheco/araa057

Kalahari tree skinks have a strong association with sociable weaver colonies. These colonies are some of the largest bird-built structures in the world and are used by many different species, both avian and non-avian, with the Kalahari tree skink being one such species. These skinks are found in greater numbers on trees with colonies than trees without. However, a predator of these skinks, the African pygmy falcon also uses these colonies. In southern Africa, these tiny birds of prey rely solely on weaver colonies for roosting and breeding. Yet, skinks do not seem to be deterred by the presence of pygmy falcons and their numbers do not differ between colonies with or without falcons.

So how are tree skinks able to live in such close proximity to a predator? "It turns out that falcons also prey on sociable weavers and as a result these weavers alarm and flee when falcons approach" said Anthony Lowney, the lead author "therefore, we wanted to see if skink behaviour was influenced by changes in weaver behaviour". To test this, they used three different approaches. First, they investigated how skinks behaved when weavers were present at a colony while predators were absent. They then compared this to how skinks behaved when no weavers or predators were present. They found that, when weavers were present, skinks were more likely to be seen basking in the open and foraging away from the safety of the tree. However, when weavers were away, skinks were less likely to be seen in the open and less likely to venture away from the tree.

Secondly, tests were carried out to see how skinks reacted when a predator (Anthony) approached the colony. This experiment was carried out on skinks in the presence of weavers and compared to the behaviour of skinks while weavers were away. "We found that, when there were no weavers, the ‘predator’ could get much closer to the skink before the skink fled for cover. When weavers were present the skinks used the fleeing weavers as a signal to also flee meaning that it was more likely that the skink would escape to cover when weavers were present".

Finally, the researchers played recordings of weavers alarm calls (made in response to falcons) and recordings of the weaver’s non-alarm contact vocalisations to skinks at colony trees. Here they found that skinks were more likely to flee for cover when presented with the alarm vocalisations but carry on with their normal behaviour (basking/foraging) when presented with the non-alarm recording. This experiment was repeated at trees without weaver colonies, the skinks here changed their behaviour, becoming more alert, when presented with the non-alarm recording. But, when they were presented with the alarm call, they were unlikely to flee for cover. "The difference between behaviours of skinks at colony trees compared to skinks at non-colony trees suggests that this behaviour is, at least partially, learnt" said Anthony "Being able to eavesdrop on weavers allows skins at colony trees to determine the likelihood of a predator being nearby. If weavers are present and relaxed, skinks can use this as a sign of relative safety. They can bask in the open and forage further away from the refuge. They also have the additional benefit of having weavers alarm if falcons approach allowing the skink more time to escape to cover. If weavers are not around, then skinks do not have this early warning system and as a result they are much more cautious and less likely to be seen in the open or foraging away from the tree. All this enables skinks to sleep with their enemy".