Social learning in otters

Abstract

The use of information provided by others to tackle life's challenges is widespread, but should not be employed indiscriminately if it is to be adaptive. Evidence is accumulating that animals are indeed selective and adopt 'social learning strategies'. However, studies have generally focused on fish, bird and primate species. Here we extend research on social learning strategies to a taxonomic group that has been neglected until now: otters (subfamily Lutrinae). We collected social association data on captive groups of two gregarious species: smooth-coated otters (Lutrogale perspicillata), known to hunt fish cooperatively in the wild, and Asian short-clawed otters (Aonyx cinereus), which feed individually on prey requiring extractive foraging behaviours. We then presented otter groups with a series of novel foraging tasks, and inferred social transmission of task solutions with network-based diffusion analysis. We show that smooth-coated otters can socially learn how to exploit novel food sources and may adopt a 'copy when young' strategy. We found no evidence for social learning in the Asian short-clawed otters. Otters are thus a promising model system for comparative research into social learning strategies, while conservation reintroduction programmes may benefit from facilitating the social transmission of survival skills in these vulnerable species.

Keywords: group living; network-based diffusion analysis; otters; problem-solving; social learning; social networks.

Figure 1.

The novel extractive foraging tasks presented to the smooth-coated otters. (1) A simple plastic box (55 × 175 × 130 mm); (2) a plastic box with clips on the lid (45 × 135 × 135 mm); this box was used as both tasks 2 and 3, once with four clips closed (task 2) and then with two clips closed and two clips removed (task 3); (4) a round plastic jar with screw-top lid (180 × 90 mm diameter); (5) a round plastic tub with a pull-off lid (70 × 170 mm diameter); and (6) a square plastic jar with screw-top lid (180 × 85 × 85 mm). Each task was baited with half a fish and covered with its respective lid. The tasks are numbered in assumed order of difficulty with 1 being the easiest and 6 being the hardest.

Figure 2.

The novel extractive foraging tasks presented to the Asian short-clawed otters. These differ from those presented to the smooth-coated otters (figure 1), as in this second iteration of the experiment on the second study species we wanted to create a more explicit range of task difficulties. Tasks were also slightly smaller to accommodate the smaller size of this otter species. (1) A simple plastic box (40 × 100 × 100 mm); (2) a plastic box with two clips (45 × 100 × 85 mm); (3) a plastic tub with a screw-top lid (130 × 75 mm diameter); and (4) a frozen reward on a bamboo cane that had to be moved up and to the right to fit through the hole. The numbering of the tasks is in intended order of difficulty, with 1 being the easiest, and 4 being the most difficult. These tasks were baited with peanuts and one fish head per task at the New Forest Wildlife Park, and peanuts and mealworms mixed with either half a mouse or day-old chick legs at Paradise Wildlife Park. Task 4 required a different type of reward due to its design, so this was a block of ice with shrimp or mealworms frozen inside.

Figure 3.

Association networks for the four otter groups. (a) Smooth-coated otters; (b–d) Asian short-clawed otters. The line thicknesses are scaled according to the strength of association between each dyad of otters. Black nodes represent males, grey nodes represent females; square nodes represent parents, circular nodes represent offspring. The numbers on the nodes represent the number of times each otter was the first individual to solve a task (i.e. the innovator).

Figure 4.

The order of solving in the smooth-coated otters for each of the six tasks. The total association of each naïve individual with informed individuals is plotted against the sequence of solving (task-solving event = 1 is when the first individual solved, etc.). Offspring are plotted as circles and parents as triangles. The individual that solved the task at each part of the sequence is plotted in red and joined with red lines. The dashed blue line shows the path we would expect the red line to take if there were no social transmission (but allowing that juveniles are faster to solve). If there is social transmission through the network the red line should be above the blue line. The solvers are labelled as Mum/Dad for parents and as Sis (sister)/Bro (brother) with ID number for offspring. In (a–d) tasks 1–4, the individual to solve the task next tends to be an offspring with a relatively high level of association to informed otters relative to others for that solve, and the red line is clearly above the dashed blue line. In (e–f) tasks 5–6, this pattern is no longer apparent.