Subject: Why do chickens lay unfertilized eggs?

Further to the questions on chickens' eggs (size and fertilization)(Jan & 
June 1999), I was wondering why chickens "waste" so much energy laying 
fully formed, unfertilized eggs. Mammals get rid of small unfertilized eggs 
and a slight thichened "just in case" endometrium, thus not wasting energy. 
Chickens don't: they make the whole package and then discard it. Do any 
other birds also lay eggs continuously? 

Re: Why do chickens lay unfertilized eggs?