Why so many collared doves

My garden is popular with black/brown birds, sparrows, robins, jackdaws, wood pigeons and collared doves but today as i fed the birds in my garden i looked up at the silver birch tree and after counting i counted a total of 19 collared doves which i was gobsmacked at the number of them together as i have never experienced so many, but what i would like to know is why so many? As i only usually see perhaps two-four at most together, so to see 19 together was a wow moment, so i am just curious?