Dove death on a nest - common??

We get quite a few Mourning Doves nesting in oak trees in our front yard, so common that I don't pay too much attention to them anymore. But we had one get on or return to an existing nest late (as it seemed to me, since several others had hatched their chicks and moved on). Her behavior was typical of a nesting mother, staying on the nest unless someone got too close to the tree.

Several weeks have gone by and on a whim I looked at the nest this morning, expecting to find it empty. To my shock I found the dove still in her nesting pose, obviously dead for some time. I obviously don't know if she was sick when she returned to the nest, but am wondering if this is a common behavior that I am unaware of?

Barry