December 2001 – vol. 94, issue 12, pp 603 When watching House Martins Delichon urbica in 1967, I wrote in my notebook: `Is the mud for the structure of their nests carried on, rather than in, their beaks?'. My impression then was that the birds carried up the mud on the beak, and pressed it into the outer fabric of the nest with a sort of rapid nodding movement. ... This article is only available to registered users.To read more, please log in or purchase a subscription.