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Biol Lett. Jun 23, 2010; 6(3): 290–292.
Published online Jan 13, 2010. doi:  10.1098/rsbl.2009.0960
PMCID: PMC2880063
Is it only humans that count from left to right?
Rosa Rugani,1* Debbie M. Kelly,2 Izabela Szelest,2 Lucia Regolin,3 and Giorgio Vallortigara1
1Centre for Mind/Brain Sciences, University of Trento, Corso Bettini 31, 38068 Rovereto, Italy
2Department of Psychology, University of Saskatchewan, Saskatoon, Canada
3Department of General Psychology, University of Padova, Italy
*Author for correspondence (rosa.rugani/at/
Received November 20, 2009; Accepted December 14, 2010.
We report that adult nutcrackers (Nucifraga columbiana) and newborn domestic chicks (Gallus gallus) show a leftward bias when required to locate an object in a series of identical ones on the basis of its ordinal position. Birds were trained to peck at either the fourth or sixth element in a series of 16 identical and aligned positions. These were placed in front of the bird, sagittally with respect to its starting position. When, at test, the series was rotated by 90° lying frontoparallel to the bird's starting position, both species showed a bias for identifying selectively the correct position from the left but not from the right end. The similarity with the well-known phenomenon of the left-to-right spatially oriented number line in humans is considered.
Keywords: avian brain, mental number line, domestic chick, Clark's nutcracker
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