title: Design complexity and strength of laterality are correlated in New Caledonian crows' pandanus tool manufacture.
abstract: Population-level laterality is generally considered to reflect functional brain specialization. Consequently, the strength of population-level laterality in manipulatory tasks is predicted to positively correlate with task complexity. This relationship has not been investigated in tool manufacture. Here, we report the correlation between strength of laterality and design complexity in the manufacture of New Caledonian crows' three pandanus tool designs: wide, narrow and stepped designs. We documented indirect evidence of over 5,800 tool manufactures on 1,232 pandanus trees at 23 sites. We found that the strength of laterality in tool manufacture was correlated with design complexity in three ways: (i) the strongest effect size among the population-level edge biases for each design was for the more complex, stepped design, (ii) the strength of laterality at individual sites was on average greater for the stepped design than it was for the simpler wide and narrow, non-stepped designs, and (iii) there was a positive, but non-significant, trend for a correlation between the strength of laterality and the number of steps on a stepped tool. These three aspects together indicate that greater design complexity generally elicits stronger lateralization of crows' pandanus tool manufacture.
authors.affiliation: Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1020, New Zealand. grhunt10@hotmail.com
authors.forename: Gavin R
authors.initials: GR
authors.lastname: Hunt
authors.forename: Michael C
authors.initials: MC
authors.lastname: Corballis
authors.forename: Russell D
authors.initials: RD
authors.lastname: Gray
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D005075:Biological Evolution; D046368:Crows / Q000502:physiology*; D004193:Discrimination Learning; D005247:Feeding Behavior; D007839:Functional Laterality; D008420:Manufactured Materials; D008606:Mental Processes / Q000502:physiology*; D009510:New Caledonia; D018515:Plant Leaves