Time spent at the colony by male and female GuillemotsUria aalgeand RazorbillsAlca torda

Abstract

Before the 2–3 weeks prior to laying, male and female Guillemots and Razorbills spent equal time at the breeding site. Subsequently the female spent progressively more time away whereas the male increased the time spent at the site, apparently to protect it. The sexes took equal shares in incubating and brooding but the female Guillemot fed the young significantly more often than did the male. Overall, the male and female spent very similar amounts of time at the colony but the male took the chick to sea, and continued to feed it, whereas the female continued to visit the site for several weeks. Thus, overall the male invested more time in rearing the chick than did the female. This was unexpected as female Guillemots are sometimes raped by neighbours, so there may be doubt as to the paternity of chicks.