Birds have brains that are comparable in size to those of mammals. However, variation in relative avian brain size is greater in birds. Thus, birds are ideal subjects for comparative studies on the ecological and behavioral influences on the evolution of the brain and its components. Previous studies of ecological or behavioral correlates in relative brain size were mainly based on gross comparisons between higher taxa or focussed on the relationships between the sizes of specific brain structures and the complexity of different tasks.Here we examine variation in dimensions of the braincase, relative overall brain size and size of its components, in reference to one general ecological and behavioral task: migration. We used data from three lineages of closely related species (14 Acrocephalines, 17 Sylvia and 49 parulid warblers). Within each group, species vary in their migratory tendencies. We found that species migrating long distances have lower skulls and smaller forebrains than resident species. We discuss four hypotheses that could explain smaller forebrain sizes, and suggest relevant taxa to use in comparative analyses to examine each of these hypotheses: -Brain size is energetically constrained. Contrasts can be made not only between migrants and residents, but also between birds in habitats with high and low levels of available food. -Brain size is developmentally constrained; birds with short growing periods should have smaller forebrains. Comparisons need to be made between birds living in habitats with long and short breeding seasons. -Bill adaptations for foraging constrain braincase dimensions. Further analyses would need to be done on groups with high variation in bill dimensions and foraging modes. -Birds with small brains have to migrate to compensate for low behavioral flexibility. Contrasts between members of families containing tropical residents and migrants need to be made.We also raise the question of whether only those parts of the brain are reduced that are most dispensable and whether brain size reduction limits foraging skills and social competence.

Voltage gated channel proteins cooperate in the transmission of membrane potentials between nerve cells. With the recent progress in atomic-scaled biological chemistry it has now become established that these channel proteins provide highly correlated atomic environments that may maintain electronic coherences even at warm temperatures. Here we demonstrate solutions of the Schrödinger equation that represent the interaction of a single potassium ion within the surrounding carbonyl dipoles in the Berneche-Roux model of the bacterial KcsA model channel. We show that, depending on the surrounding carbonyl derived potentials, alkali ions can become highly delocalized in the filter region of proteins at warm temperatures. We provide estimations about the temporal evolution of the kinetic energy of ions depending on their interaction with other ions, their location within the oxygen cage of the proteins filter region and depending on different oscillation frequencies of the surrounding carbonyl groups. Our results provide the first evidence that quantum mechanical properties are needed to explain a fundamental biological property such as ion-selectivity in trans-membrane ion-currents and the effect on gating kinetics and shaping of classical conductances in electrically excitable cells.

In this paper we briefly discuss the necessity of using quantum mechanics as a fundamental theory applicable to some key functional aspects of biological systems. This is especially relevant to three important parts of a neuron in the human brain, namely the cell membrane, microtubules (MT) and ion channels. We argue that the recently published papers criticizing the use of quantum theory in these systems are not convincing. 1) Quantum theory and biological systemsBiological systems operate within the framework of irreversible thermodynamics and nonlinear kinetic theory of open systems, both of which are based on the principles of nonequilibrium statistical mechanics. The search for physically-based fundamental models in biology that can provide a conceptual bridge between the chemical organization of living organisms and the phenomenal states of life and experience has generated a vigorous and so far inconclusive debate [1,2]. Recently published experimental evidence has provided support for the hypothesis that biological systems use some type of quantum coherence in their functions. The nearly 100% efficient excitation energy transfer in photosynthesis is an excellent example [3]. Living systems are composed of molecules and atoms, and the most advanced physical theory describing interactions between atoms and molecules is quantum mechanics. For example, making and breaking of chemical bonds, absorbance of frequency specific radiation (e.g. in photosynthesis and vision), conversion of chemical energy into mechanical motion (e.g. ATP cleavage) and single electron transfer through biological polymers (e.g. in DNA or proteins) are all quantum effects. Regarding the efficient functioning of biological systems, the relevant question to ask is how can a biological system with billions of semi-autonomous components function effectively and coherently? Why providing a complete explanation remains a major challenge, quantum coherence is a plausible mechanism responsible for the efficiency and co-ordination exhibited by biological systems [4].

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