Technical innovations drive the relationship between innovativeness and residual brain size in birds

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: Keywords: behavioural flexibility innovation cognition comparative method foraging generalism opportunism tool use The hypothesis that large brains allow animals to produce novel behaviour patterns is supported by the correlation between brain size, corrected for body size, and the frequency of foraging innovations reported in the literature for both birds and primates. In birds, foraging innovations have been observed in over 800 species, and include behaviours that range from eating a novel food to using tools. Previous comparative studies have quantified innovativeness by summing all reports of innovative behaviour, regardless of the nature of the innovation. Here, we use the variety of foraging innovations recorded for birds to see which of two classic hypotheses best accounts for the relationship between innovativeness and brain size: the technical intelligence hypothesis or the opportunistic-generalism intelligence hypothesis. We classified 2182 innovation cases into 12 categories to quantify the diversity of innovations performed by each of 76 avian families. We found that families with larger brains had a greater repertoire of innovations, and that innovation diversity was a stronger predictor of residual brain size than was total number of innovations. Furthermore, the diversity of technical innovations displayed by bird families was a much better predictor of residual brain size than was the number of food type innovations, providing support for the technical intelligence hypothesis. Our results suggest that the cognitive capacity required to perform a wide variety of novel foraging techniques underpins the positive relationship between innovativeness and brain size in birds. We include a summary of innovation data for 803 species as Supplementary Material. Some species have much larger brains than would be expected given their body size (e.g. Corvus moneduloides; Cnotka et al. 2008), while others have much smaller ones (e.g. Colinus virginianus; Striedter & Charvet 2008). Various researchers have suggested that large brains have been naturally selected because they increase an individual's capacity to process information about social companions (Dunbar 1998), prey that are numerous or difficult to track in space and time (Eisenberg & Wilson 1978), prey that are difficult to catch and handle (Milton 1988), or variable environmental conditions (Schuck-Paim et al. 2008). It has also been suggested that increased brain …