The young of both Guillemot Uria aalge and Razorbill Alca torda have an intermediately precocial pattern of development (Sealy 1972). That is, the juvenile is led out to sea by one adult, usually the male parent (Birkhead 1984), when its wing development is sufficient for fluttering down from the cliff and diving, but when it has reached only one-third to one-half of the adult weight (Birkhead 197
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