Animals with a high rate of innovative and associative-based behavior usually have large brains. New Caledonian (NC) crows stand out due to their tool manufacture, their generalized problem-solving abilities and an extremely high degree of encephalization. It is generally assumed that this increased brain size is due to the ability to process, associate and memorize diverse stimuli, thereby enhancing the propensity to invent new and complex behaviors in adaptive ways. However, this premise lacks firm empirical support since encephalization could also result from an increase of only perceptual and/or motor areas. Here, we compared the brain structures of NC crows with those of carrion crows, jays and sparrows. The brains of NC crows were characterized by a relatively large mesopallium, striatopallidal complex, septum and tegmentum. These structures mostly deal with association and motor-learning. This supports the hypothesis that the evolution of innovative or complex behavior requires a brain composition that increases the ability to associate and memorize diverse stimuli in order to execute complex motor output. Since apes show a similar correlation of cerebral growth and cognitive abilities, the evolution of advanced cognitive skills appears to have evolved independently in birds and mammals but with a similar neural orchestration.

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Cnotka et al., 2008; Mehlhorn and Rehkämper, 2009). Several orientation cues and mechanisms -olfactory cues, visual landmarks, sun compass, magnetic compass -are known to be involved in homing behaviour, and parameters such as motivation and experience are also known to be important for fast and successful homing (Papi et al., 1974;Visalberghi and Alleva, 1975; SchmidtKönig, 1990;Bingman, 1993; Lipp, 1996;Walcott, 2005). The brain of homing pigeons is an example of mosaic evolution, which means that subsystems of the brain might follow different trends of (size) alteration independently from others (Mayr, 1963;Barton and Harvey, 2000; Rehkämper et al., 1988;Rehkämper et al., 2008). It seems to be functionally adapted to homing with several differences To show in what way lateralisation is reflected in brain structure volume, and whether some lateralisation or asymmetry in homing pigeons is caused by experience, we compared brains of homing pigeons with and without navigational experience referring to this. Fourteen homing pigeons were raised under identical constraints. After fledging, seven of them were allowed to fly around the loft and participated successfully in races. The other seven stayed permanently in the loft and thus did not share the navigational experiences of the first group. After reaching sexual maturity, all individuals were killed and morphometric analyses were carried out to measure the volumes of five basic brain parts and eight telencephalic brain parts. Measurements of telencephalic brain parts and optic tectum were done separately for the left and right hemispheres. The comparison of left/right quotients of both groups reveal that pigeons with navigational experience show a smaller left mesopallium in comparison with the right mesopallium and pigeons without navigational experience a larger left mesopallium in comparison with the right one. Additionally, there are significant differences between left and right brain subdivisions within the two pigeon groups, namely a larger left hyperpallium apicale in both pigeon groups and a larger right nidopallium, left hippocampus and right optic tectum in pigeons with navigational experience. Pigeons without navigational experience did not show more significant differences between their left and right brain subdivisions. The results of our study confirm that the brain of homing pigeons is an example for mosaic evolution and indicates that lateralisation is correlated with individual life history (experience) and not exclusively based on heritable traits.Key words: homing pigeon, lateralisation, asymmetry, brain, navigation, mosaic evolution. THE JOURNAL OF EXPERIMENTAL BIOLOGY2220 from other domestic pigeon breeds or their wild ancestors, the rock doves (Columba livia) (Haase et al., 1977;Rehkämper et al., 2008). These differences become manifest, for example, in larger hippocampi or olfactory bulbs, which are both involved in homing (Bingman et al., 2003;Bingman et al., 2005;Wallraff, 2005;Rehkämper et al., 2008). To date it has been shown that a ...

Homing pigeons are well known as good homers, and the knowledge of principal parameters determining their homing behaviour and the neurological basis for this have been elucidated in the last decades. Several orientation mechanisms and parameters-sun compass, earth's magnetic field, olfactory cues, visual cues-are known to be involved in homing behaviour, whereas there are still controversial discussions about their detailed function and their importance. This paper attempts to review and summarise the present knowledge about pigeon homing by describing the known orientation mechanisms and factors, including their pros and cons. Additionally, behavioural features like motivation, experience, and track preferences are discussed. All behaviour has its origin in the brain and the neuronal basis of homing and the neuroanatomical particularities of homing pigeons are a main topic of this review. Homing pigeons have larger brains in comparison to other non-homing pigeon breeds and particularly show increased size of the hippocampus. This underlines our hypothesis that there is a relationship between hippocampus size and spatial ability. The role of the hippocampus in homing and its plasticity in response to navigational experience are discussed in support of this hypothesis.