SIRS,--In "Some Notes on t h e Diurnal Song of Birds " (antea, p . 4) Mr. Marples states t h a t on t h e average t h e Blackbird, a t Inverness, begins t o sing in the morning 74 minutes earlier than Blackbirds do i n Hampshire, t h a t is, after correction for effect of difference of latitude on time of sunrise. Since twilight lasts longer in the north t h a n in t h e south, it is t o be expected...

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