Carolina Wrens - is nest abandoned?

I have been watching for the last few weeks as two wrens have been building a nest in the fern plant on the back porch. The mama has been sitting in the nest for maybe the past 4 or 5 days. Now, earlier today, I noticed the pair of wrens starting a NEW nest in the birdhouse we were inspired to put up in the back yard, about 15 yards from their first nest. For the moment, neither of the birds is to be seen and I can see there are 3 eggs in the fern plant nest. Where did the wrens go? It's chilly out, (in South Carolina standards), at 58degrees Farenheit. Isn't that too cold for the eggs? Should I put a heat lamp on the nest? I don't dare to do anything for fear of disturbing them, but I don't want the eggs to die either.

Probably deserted, yes. Most likely, the wrens realised their nest had been discovered by a potential predator (cat, raccoon, snake, jay, human, etc., etc., etc) and it is safer for them to start over, rather than trying to continue in a place where they risk being caught. Not much you can do about it.

Resin