In the summer of 2010, we had a pair that laid 11 eggs in total (6 & 5). We had a cold spell (blizzard for 2 days) while they were incubating ... so when able we took a suet mixture down to them. They learned very quickly that it was for them and they became very territorial and would shoo the grey catbirds and song sparrows away, but allowed the Chickadees to feast on it. Thought that was interesting as the Chickadees would follow us for seeds & peanuts.
*Bluebirds are my favourite birds and I did not see one until 2004. Having them nest on the property has been a dream come true. However, they have to compete with the Tree Swallows. When the House Wrens come they have been rather vicious ... they killed the Tree Swallows (pierced the neck while incubating broods) and have pierced eggs.
In 2018, 2019 & 2020 Eastern bluebirds occupied house #4.