Reproductive Synchrony and Extra-pair Copulation in Birds


Zoology Department, The University, Sheffield S10 2TN, U.K.

Department of Probability and Statistics, The University, Sheffield SS3 7RN, U.K.


We present a model which explores the idea that females may reduce their risk of suffering a forced extra-pair copulation, by breeding synchronously with other females in the population. Information from three bird species with contrasting ecology and behaviour shows that synchrony does not automatically confer an advantage on females: synchrony is only advantageous to females if certain conditions pertain. We identify three main factors which influence female extra-pair copulation risk, these are: (i) whether or not males can identify fertile females, (ii) male and female ‘availability’ (e.g. in some seabirds copulation and extra-pair copulations occur only at the colony: females may be absent for long periods and hence are unavailable for extra-pair copulations), (iii) the timing of extra-pair copulations by males, relative to when their partners lay.