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Summary.  There is a large non‐breeding population of Fulmars and other Pro‐cellariiform birds, which suggests that they do not breed annually.  In non‐breeding Fulmars obtained in northern Labrador in July it was found that the length of the middle claws varied from 16.0 to 10.6 mm., due to wear. As pelagic birds can only wear down their claws when breeding, this observation strongly suggests a non‐breeding population of mixed age‐groups.  Ovaries from four representative non‐breeding females were sectioned, and histological confirmation obtained of the relation of claw‐length to age. Resorbed remnants of ovulated follicles prove that all these birds had bred in one or many previous years, and thus that their reproduction is intermittent.  A case of follicular atresia accompanied by the extrusion of yolk into the stroma is figured.  When breeding is inhibited in the Fulmar and certain other birds the annual (post‐nuptial) moult occurs prematurely. A short discussion is given of other effects of inhibited breeding in marine birds.

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