How can Darwinism explain the reason of the existance of so many creatures for instance numerous types of birds?

Darwin provided a theory, not an all encompassing explanation.

I am not sure what you are after. A population of a specie change by adaptation to changed conditions or by gaining an advantage. The specie they evolved from might still survive and then you have something called evolutionary branching. When this happens many times in evolutionary history you get a multitude of species and variations. This is the core of the theory really. Biological evolution is not about one specie that comes out of one that disappears.

Most – if not all – life on the planet is related. A tree’s cell can read your dna. We all come from the same root.

I don’t understand the question.

Evolution and Natural Selection, which is influenced by other animals and the location the animal exists in. Please use these two terms to read more information from credible sources. Your question will be answered. Don’t be confused with Darwinism too much before you look into the underlying premises of evolution and natural selection. They easily explain why there are a variety of species of birds and other animals.

Darwin actually explains this quite nicely in his book On the Origin of Species.

The basic principle is that species are shaped by the ecological niche in which they live. The aim of each species is to maximise it’s abilty to utilise resources while minimsing competion from other species. For example the type of food they specialise in eating will shape the beak, teeth, jaw or what ever. Body shape will also be affected by the nesting site, climate, presence or absence of predators, how the species atracts a mate etc.

Not all members of a species encounter the same selecting factors, so they will naturally diverge in isolation from each other. This is exactly what Darwin’s classic example of the Galapagos Finches highlights.

@FireMadeFlesh Nice and short.

Thanks @oratio! I often can’t be bothered reading long responses, and today I can’t be bothered writing them.