Berries can be rich with sugar and, at this time of year, provide a great source of food for birds. Birds have competition from humans when it comes to blackberries.
Humans also go for elderberries although they don’t agree with everybody and are best made into drinks.
Not many humans would try the red berries even if they came from the Guelder Rose.
The Mountain Ash berries will probably not be eaten by birds until they are ripe or food is more scarce.
Birds must also, as needs must, eat the berries of Lords and Ladies to help disperse the seeds. They do not tempt many humans with their clammy poisonous look.