Eric makes an interesting point about house sparrows and bluebirds.
Another angle on this is that while it is tempting to think of the
sparrows as being some sort of alien intruder wreaking havoc on our
native bluebirds, it is not so clear-cut as that. For millennia up until
about 200 years ago VT was largely forest and bluebirds were probably
very unusual in our area. They  "invaded" following the cutting down of
the forests and their replacement with artificial grasslands. So, they
are just as dependent on man as the house sparrows are and, like
sparrows, their presence in the state is a result of human development.
Now that the state is reforesting back to its "natural" condition,
bluebirds are losing habitat and facing nest site competition with
sparrows (and other species like house wrens and tree swallows). While I
appreciate that seeing bluebirds being ousted may be unpleasant, is it a
legitimate conservation strategy to try to maintain "unnatural" habitats
and their occupants in Vermont, or should we just recognize that they
are alien and let them go? 
 
 
 
 
 
Hector Galbraith PhD
Galbraith Environmental Sciences LLC
837 Camp Arden Rd., Dummerston, VT05301
802 258 4836 (phone)