Constraint vs Parameter - way to force collection as parameter

Question

I am wondering if there is any difference between these two methods. Second one look more natural, but that shouldn't be the only reason to use it. Maybe there are some performance issues or some diabolic mambojambo related to any of them?

void FirstMethod<T>(T a) where T : IEnumerable<Animal>
{
    ...
}

void SecondMethod<T>(IEnumerable<T> a) where T : Animal
{
    ...
}

Answer 1

The difference is that you can easily pass IEnumerable<Dog> to the second method, but when you pass it to the first method it'll just be implicitly converted to an IEnumerable<Animal>

Take a look at the fiddle

Edited Thanks @Servy for comment.