Diet modulates behaviour in house sparrows: insights into possible hormone-mediated mechanisms.

Foraging animals usually select foods that balance the intake of key nutrients, for example essential amino acids that cannot be synthesized and must be obtained from the diet. However, the ability to gain optimal ratios, proportions and amounts of nutrients may be hampered by a changing environment, competitive conspecifics or species and predators. Here, we used an experimental system in which house sparrows, Passer domesticus , were fed a manipulated diet with different compositions of amino acids (in the experimental diet phenylalanine and tyrosine content was 42% of that in the control diet). Phenylalanine and tyrosine are precursors of coping hormones: dopamine, noradrenaline (norepinephrine) and adrenaline (epinephrine) which are involved mainly in the expression of stress and fear, but also in learning and long-term memory formation. Accordingly, birds fed a diet deficient in these amino acids learned to avoid unpalatable food markedly slower, coped worse with stress in the presence of a novel object and were more aggressive towards other sparrows than control birds. Surprisingly, circulating amounts of the catecholamines in blood plasma were higher in these birds than in sparrows on the control diet. This study provides the first evidence that variation in amino acid composition in the diet is associated with variation in behaviours and hormone levels in birds. We conclude that food, besides its nutritional function, seems to represent one of the modulators of behavioural expression making a balanced diet crucial for survival. • Animals balance the intake of key nutrients such as essential amino acids. • An imbalance of amino acids may result in behavioural changes. • Birds on an imbalanced diet learned slower and were more aggressive and stressed. • Food seems to represent one of the main modulators of behaviour. [ABSTRACT FROM AUTHOR]