egg question

So I'm looking into getting doves. I have my heart set on getting a pair of female ring-neck doves. It will have to wait a bit until I move into my new place but I figure that just gives me time to prepare. (#1) My biggest question is regarding eggs. I have been trying to find information but...

Hi everyone My hen laid first egg two days ago. She doesn't lay her second egg after one day gap. Now after 2 days I find a small egg in bowl. Can a sparrow do this? Can she lay a egg in pigeon nest? Sparrows do come in my loft. What should I do? I'm attaching pic