My baby dove shivers after I feed it. Should I be concerned?

About a week ago I stumbled upon two baby doves, both on the hot pavement floor. One was evidently dead and the other one still moving. I manged to save the baby dove and give it a living space that is approx 80 degrees (have a themo attached to area). It has clean kitchen towels inside it's area to retain heat. It seems fine...however, every time I take it out and finish feeding it (with heated 'exact' baby bird hand feeding formula) it seems to ruffle up it's feathers and shiver for about five minutes and sometime more, all while falling asleep. I'm not concerned with it's sleeping. I'm sure it's pretty normal for a baby dove to sleep after eating but it shivers a lot then finally settles down. is it in a sort of hibernation state? Is it just content? Or is it cold somehow?? I'm not sure. I occasionally take a clean sock put 2/3 of white rice in ,heat it up in the microwave, and set it down next to the bird for extra warmth. Oh, and it also has a small heating lamp. is this enough?