SIRS,--The observations conducted b y Messrs. Ingram and Salmon on the dives of the Long-tailed Duck (antea, p . 264) reopen a veryinteresting question, and one which, I think, is still some way from being satisfactorily answered. In estimating the average duration of a dive of a given species, t h e only reliable figures we can hope t o give, in the present state of our knowledge, are those of bi...

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