Since you're concerned about the potential toxicity of the prunus padus to birds, I'll address that.
The fruit from the tree is not only safe for birds, but is actually a healthy part of their diet. It supplies them with needed vitamins and nutrients. Sources generally agree that, even though they're edible, the seeds are undigestible for birds. Therefore, they expel them, where they become a benefit to various types of mammals.
The fruit which is roughly the size of a pea, although edible, has a very bitter taste and contains a poisonous stone but birds such as the Robin, Redwing, Blackbird and Fieldfare, as the trees name suggests, love them, providing them with a valuable source of vitamin C and other minerals. The seed is not digested by the birds and is therefore distributed far and wide through their droppings. Apart from being an important food source for birds, many small mammals benefit from any of the fallen fruit. Source
Like wild cherry, the spring flowers provide an early source of nectar and pollen for bees, while the cherries are eaten by birds including the blackbird and song thrush, as well as mammals such as the badger, wood mouse, yellow necked mouse and dormouse. Source.
Birds are also an important part of helping the tree thrive in your garden.
The insects such as beetles and bees that pollinate bird cherry benefit from the nutrients in the flowers' nectar, while at the same time providing the essential service of pollination to the tree. Despite their bitter taste, the fruits of bird cherry are eaten by birds, especially robins (Erithacus rubecula), starlings (Sturnus vulgaris) and members of the thrush family (Turdus spp.), and are relished as some of the earliest fruit to be available in the summer. While the birds benefit from this food, the tree also gains, by having its seeds dispersed in the birds' droppings. Source
You didn't mention whether or not you have livestock, either in your garden or nearby. If so, please don't plant these trees. They're highly toxic to farm animals, especially goats.
The foliage is eaten by caterpillars of many species of moth, including the orchard ermine, brimstone and short cloaked moth, however it is toxic to livestock, particularly goats. Source