Mean number of eggs laid per week for the 28 years data were available from 1969–2014 (total eggs = 1143). Survey in second week of September (week 11) ensures that all early breeding attempts will be recorded (except those that have failed with no evidence left) and survey in the second week in November (week 20) allows all but 3.1% of breeding attempts to be recorded with some chance of establishing nestling age.