Q:

Owners in groovy closures

According to "Groovy in Action", closures can be declared via several ways.  A couple of ways:
def printer = { line -> println line }
def Closure getPrinter() {
    return { line -> println line }
}
According to Closures, official documentation owner in closure 

"return the direct enclosing object, be it a closure or a class." 

Ok, let's have a look at:
class Mother {
    def prop = 'prop'
    def method(){ 'method' }
    Closure birth (param) {
        def local = 'local'
        def closure1 = {
            [ this, prop, method(), local, param ]
        }
        return closure1
    }

    def birth2 = { param ->
        def local = 'local'
        def closure2 = {
            [ this, prop, method(), local, param ]
        }
        return closure2
    }
}
Mother julia = new Mother()
def closure = julia.birth('param')
assert closure.owner == julia
assert closure.delegate == julia

def closure2 = julia.birth2('param')
assert closure2.owner == julia  
assert closure2.delegate == julia

In both cases, birth anb birth2 are closures according to documentation.  Inside these closures we declare closure1 and closure2.  I gave them names just to refer to them.  The owners of these closure1 and closure2 should refer to birth and birth2.  According to the official documentation.  But in first example owner refers to instance of class - julia.  In the second example, I believe it refers to birth2, but don't know how to assert it.  
Can anyone explain the difference, please? 

A:

birth is a method, not a closure
birth2 is a closure
Therein lies the difference

