Abstract
Tooling is associated with complex cognitive abilities, occurring most regularly in large-brained mammals and birds. Among birds, self-care tooling is seemingly rare in the wild, despite several anecdotal reports of this behaviour in captive parrots. Here, we show that Bruce, a disabled parrot lacking his top mandible, deliberately uses pebbles to preen himself. Evidence for this behaviour comes from five lines of evidence: (i) in over 90% of instances where Bruce picked up a pebble, he then used it to preen; (ii) in 95% of instances where Bruce dropped a pebble, he retrieved this pebble, or replaced it, in order to resume preening; (iii) Bruce selected pebbles of a specific size for preening rather than randomly sampling available pebbles in his environment; (iv) no other kea in his environment used pebbles for preening; and (v) when other individuals did interact with stones, they used stones of different sizes to those Bruce preened with. Our study provides novel and empirical evidence for deliberate self-care tooling in a bird species where tooling is not a species-specific behaviour. It also supports claims that tooling can be innovated based on ecological necessity by species with sufficiently domain-general cognition.
Highlights
Tooling is associated with complex cognitive abilities, occurring most regularly in large-brained mammals and birds
Tool use behavior—including but not limited to tooling—has been regarded as a marker of complex cognition across birds and m ammals[4,7,8], a link which has led to considerable interest in the field[3,9,10,11,12]
Most reports of tooling in birds revolve around foraging[9,10,11,12,14,15,20,21,23,24,25]. Among parrots this is more common in captive settings, for example, greater vasa parrots use small stones to scrape or break up shells, which they ingest[23], hyacinth macaws use wedges to manipulate nuts[20], and Goffin’s cockatoos innovate and manufacture stick tools to retrieve out-of-reach food[19]
Summary
Tooling is associated with complex cognitive abilities, occurring most regularly in large-brained mammals and birds. There are anecdotal and video reports of several parrot species innovating self-care tooling in captivity, primarily by holding sticks or other objects with their feet to scratch t hemselves[9,10,30]. A study reported self-care tool use in Atlantic puffins (Fratercula arctica), which were observed holding sticks to their bodies, possibly in order to scratch themselves[28]. This claim rests on two observations across four years of two puffins living in colonies over 7000 km apart (in Wales and Iceland), for which only one tool use instance was recorded on video.
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