They are a little smaller. The main obvious difference is a black spot on the side of their head - the male and female look alike also.
Here is a link to a picture.
http://epsc.wustl.edu/~rlk/wgnss/ets/Actually the sparrow came back again and tried to feed them later on in the day and when the wren was harassing the bird for getting too near to it's chicks the sparrow went inside (did several times but didn't seem to be harming them). I was going to put a 1" hole restrictor on it but don't want to trap the sparrow inside - I am not sure if it left or not.
I'm going to leave well enough alone tonight. The only thing I can think of is maybe the bird lost it's chicks or something. This was a eurasian sparrow's nest last year - I guess it could have been hers. I get only the Eurasian ones in these houses cause I put hole restrictors on them that the house sparrows can't get in, but the Eurasian ones can. The wren's a little smaller though. I'm happy to have the wrens make there house there - I just hope neither hurts the other or the babies.
Meg