The first three years of data collection our most populous species was the Dark-eyed Junco, Junco hyemalis.  House Sparrows, Passer domesticus, also known as English Sparrows had never been observed at our feeding station.  Then during the 1999 – 2000 school year we saw a dramatic drop in the Dark-eyed Junco population and experienced a huge influx of House Sparrows.  The effect was impressive enough to catch the attention and concern of nearly all of my students.  Why was this happening?  Was it a coincidence?  Did the construction of houses and the loss of the field behind our school have something to do with this change?  Were the House Sparrows driving away the Juncos?