My first was a Blackbird with 2 eggs (I had seen the female sitting earlier) on 19th March at Saville Park.
Today a newly built but as yet unused Blackbird's nest at Barkisland.
In the same garden I watched a Dunnock back to it's nest with material in its beak. It soon came out and when I looked the nest was complete and may have the first egg tomorrow. I won't go to it tomorrow, but in two days it is likely to have forgotten my visit today, if it saw me. Then when the clutch is started it is unlikely to desert as long as I don't visit every day. I will only visit once to check first egg date, secondly for total clutch size, a third time to check on whether nestlings have hatched, and then well after fledging time to check on success and for any addled eggs/ repeat clutch.
The turquoise colour of Dunnocks' eggs is marvelous, and recording details of common birds nests is valuable in Integrated Population Monitoring.
Nest records with only two visits are also valuable, as long as some change takes place between the visits, and the adults' behaviour noted.
Details at www.bto.org.uk/volunteer surveys