An Investigation of the Factors Driving Cognition in Darwin's finches

The use and manufacture of tools has been considered to be cognitively demanding and thus a possible evolutionary driving factor of intelligence. Animal tool-use provides the opportunity to investigate whether the use of tools evolved in conjunction with enhanced physical cognitive abilities. However, success in physical tasks may simply reflect enhanced general learning abilities and not cognitive adaptations to tool-use. To distinguish between these possibilities, we compared general learning and physical cognitive abilities between the tool-using woodpecker finch (Cactospiza pallida) and its close relative, the small tree finch (Camarhynchus parvulus). Since not all woodpecker finches use tools, we also compared tool-using and non-tool-using individuals, predicting that domain-specific experience should lead tool-using woodpecker finches to outperform non-tool-users in a task that is similar to their natural tool-use. Contrary to our predictions, woodpecker finches did not outperform small tree finches in either of the physical tasks and excelled in only one of the general learning tasks, and tool-using woodpecker finches did not outperform non-tool-using woodpecker finches in the physical task closely resembling tool-use. Our data provide no evidence that tool-use in woodpecker has evolved in conjunction with enhanced physical cognition or that domain-specific experience hones domain-specific skills. This is an important contribution to a growing body of evidence indicating that animal tool-use, even that which seems complex, does not necessitate specialized cognitive adaptations. One of the fundamental issues in the study of human and animal cognition concerns the factors that drove the evolution of intelligence. The ability to use tools has played a long-standing role in this debate because it is thought to be cognitively demanding (e.g. Parker and Gibson 1977, but see also Hansell and Ruxton 2008). If tool-use poses a cognitive challenge and provides a selective advantage in acquiring resources, then we would expect that enhanced cognitive abilities should have evolved to increase the effectiveness of tooluse or to enable the development of such an unusual technique in the first place. The notion that tool-use should be linked to cognition related to learning about the physical world, for example the spatial relationships between objects, connectivity and weight, has been 18 The factors driving cognition in Darwin’s finches particularly popular amongst cognitive biologists and has generated many studies of toolrelated cognition in primates (Hauser et al. 1999; Martin-Ordas et al. 2008; Povinelli 2000; Santos et al. 2006; Seed et al. 2009; reviewed in Visalberghi and Tomasello 1998) and birds (e.g. Auersperg et al. 2009; Kacelnik et al. 2006; Seed et al. 2006; Taylor et al. 2008; von Bayern et al. 2009; Wimpenny et al. 2009; reviewed in Emery and Clayton 2009). Some of the strongest evidence supporting the notion that tool-use is linked to enhanced cognition is the strong correlation between tool-use and brain size in birds (lefebvre et al. 2002) and primates (reader and laland 2002) as well as the demonstration that the cerebellum of toolusing birds has a higher degree of folding than that of non-tool-using birds (Iwaniuk et al. 2009). However, these findings provide only an indirect demonstration of the connection between tool-use and enhanced cognition and must be confirmed by behavioural experiments conducted in a comparative framework. Several comparative methods are available to demonstrate that a given character, behaviour or cognitive trait is related to an ecological condition (e.g. Harvey and Pagel 1991; Shettleworth 1998). Traditionally, two approaches have been taken: the search for character divergence in closely related species under differing selective conditions and the search for convergence amongst unrelated species due to similar selective conditions. While these approaches are both necessary and informative by themselves, it is only through the synthesis of the two and by gathering repeated observations of the same pattern of convergence and divergence in several evolutionarily distinct groups that we can possibly begin to understand the true relationship between tool-use and physical cognition. The woodpecker finch (Cactospiza pallida) is a tool-using species that habitually uses twigs or cactus spines to poke arthropods out of tree holes (Eibl-Eibesfeldt 1961). Experiments have demonstrated that juvenile woodpecker finches acquire the ability to use tools in distinct developmental stages independently of whether or not they are raised with a toolusing model, indicating that this ability is based on a specific genetic predisposition and is not dependent on social learning (Tebbich et al. 2001). In this study, we compare cognition in woodpecker finches, a species that habitually uses tools, and the closely related non-tool-using small tree finch (Camarhynchus parvulus). These two Darwin’s finch species are both members of the tree finch clade within the Darwin’s finches and are found sympatrically throughout Santa Cruz Island of the Galápagos archipelago—these similarities minimize the influence of contextual variables as explanations for differences in cognitive abilities. The main objective of this study was to see whether this species pair shows a divergence in cognitive abilities apart from the genetic predisposition to acquire tool-use. Such cognitive divergence could be limited to evaluation of inputs from the domain of tool-use, for example, appreciation of the functional relationship between a tool and the object that it moves. To test the hypothesis that tool-use in woodpecker finches co-evolved with enhanced physical cognitive abilities, we compared their performance with that of small tree finches in two tasks designed to test different aspects of physical cognition. The physical tasks can be