She should not abandon the nest if she can get the dead nestling out, it would be better if you took it and left the other one. If she cant get it out she may abandon the other one because most birds are very clean and will not risk disease spreading. If she cant get the dead nestling out the other one runs the risk of getting something and so does she.
Another problem is that if she doesn't see you move it she may think that a predator has been sneaking around and taken it so will most likely write the other chick off as dead and go and start again somewhere else. If she sees you taking it and you don't disturb it again, often they accept that humans are no threat.
Where you using a power tool? I hear or so many people killing wildlife by accident from using power tools, they should be banned for this reason alone. Or maybe the wood just fell.
Blackbirds often build their nests low but I've never seen one on the grown, just very low to the ground. Without a description of the birds or a photo its hard to know what bird it was.
Scent does have major effect, but that depends on the type of bird. Chances are even if it's a bird that does not care about human scent, the death will mean the nest is going to be abandoned and a new one will be made somewhere else
I accidentally harmed a baby bird in its nest while edging around the yard, which resulted in the death of the bird. However- another baby bird was unharmed. Will the mom still come back and feed it/ nurture it even if she has a dead baby bird in the nest? Also, I touched the baby bird in an effort to examine it to see if it was harmed. (So it has my scent on it.) i'm unsure on what kind of bird it was- but the nest was on the ground underneath a piece of plywood. I can tell that the nest was built there- it wasn't knocked down to the ground.
