Woodpigeon babies with no mum


Last week I observed a pigeon sitting on a nest in our crabapple tree for several days in a row. 

I looked yesterday to find there are two babies (seemingly a bit larger than I was expecting) so perhaps older than I know of. 

I haven't seen the mum though and been keeping an eye out all today but still no mum. 

Been trying to find info to see how long the mum leaves the nest at a time as I am worried and want to make sure the babies are OK. 

I climbed a ladder and took a closer look and they seem well enough. Moving around but no chirping or noise making. 

Any advice or guidance?