The present study shows that pigeons organise breeding
relieves such that their clutch is light exposed for about a minute
during each changeover. Relieves seem to take place as a quite
stereotyped behaviour with a rather fixed duration. Daily variances
in light exposure are therefore primarily a function of the
variances in the number of relieves. With about 15 relieves per
day, total light exposure time during a 17-day long breeding
period is about 4 h. Cumulative light exposure for the critical
tectofugal period (days 14–17) is close to 1 h.