In the Texas Hill Country bluebirds used to be common. I'm not claiming that their decline is due to house sparrows, but it's clear that house sparrows can be quite harmful to many cavity-dwelling native birds. They can be extremely desrtuctive; it is not uncommon for them to kill both parents and offspring to take over a nest or nesting spot. One of many resources on the topic:
http://bluebirdnut.com/house-sparrows/