Expert: Roger Lederer - 8/21/2011

Question
I have a cardinal nesting in my backyard in a mulberry tree.  I have been watching the process from building to sitting on eggs.  Everything I've read says that gestation is no more than 13 days.  It's been at least two weeks, maybe even two or three days more, that the female has been sitting in the nest.  Is it possible that the eggs weren't fertilized?  If so, when would she realize that?  I also understand that cardinals have two broods per year, but that the last one is usually by July.  However, I live in Florida and it stays warm a lot longer here.

Thank you,
Nina

Answer
Two weeks is about average for incubation time AFTER the last eggs is laid . (Gestation does not occur in birds, only mammals.) Maybe the eggs hatched and she is sitting on the young. If it is indeed two weeks after the last eggs was laid then perhaps the eggs are sterile. If so, she may incubate them for another two weeks or so, in a futile effort. Cardinals may have 1-3 broods a year, depending on the age of the bird, temperature, food. etc.
Also, if you have been looking at the nest frequently and disturbing the bird, (not an accusation, just an observation) and she spent more than the usual time off the nest, then the eggs may have gone bad because of the interruption. Approaching the nest once a day is plenty.