nest of cotton

Yesterday, while walking with my dog on another lovely spring morning, I found a robin's egg in the grass. I looked at it for a moment, surveying the shell for damages. I scooped it up and felt the weight in my hands. Poor baby. The egg was ice cold from the previous night and wet with dew. No imperfections. Was this egg kicked out of the nest intentionally ? Did something happen, a squirrel invader perhaps? The heaviness of the egg made me sad, I gently grasp it in the palm of my hand. Was it really too late? Could I somehow manage to warm it?

A potential life lost.

At the same time I am pleased to hold it; the shell so smooth, the shape perfect, the color, that ethereal blue. I have an urge to blow warm breaths onto the chilled egg. I know it doesn't matter at this point, but I do feel this way. I bring it inside, and put it in a sunny window. I know I am being silly now. I think about surrounding it in cotton, making a nest. I don't of course. Then I start wondering about practicalities. What if the egg warmed up and the baby bird hatched, only to fall off the window ledge, or for my cats to eat it.
How long can I keep this baby egg?

I don't want to see what is inside.
I have seen it on the sidewalks before.