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M. Ramenofsky, J. M. Gray, R. B. Johnson, Behavioral and Physiological Adjustments of Birds Living in Winter Flocks, Ornis Scandinavica (Scandinavian Journal of Ornithology), Vol. 23, No. 3, Proceedings of the Symposium Hormones, Physiology and Non-Reproductive Behaviour in Birds, 21-23 August, 1991, Göteborg, Sweden (Jul. - Sep., 1992), pp. 371-380
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Ramenofsky et al. (1992) studied this question.
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