From figure 1 in: J.M.C. HUTCHINSON 2002. Two explanations of the dawn chorus compared: how monotonically changing light levels favour a short break from singing. Animal Behaviour 64:527-539. Abstract and pdf version.

[Figures of singing routines (dawn chorus, etc.) generated by optimality model]

Optimal singing routines with sudden transitions between night and day and with (a) stochasticity in overnight energy requirements, or (b) no such stochasticity. Continuous line = % of unpaired members of the population singing; horizontal dash = switchpoint level of reserves above which singing is best; vertical bar = mean level of reserves in unpaired members of population.
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