What happened to MN bluebirds

Last summer not a single bluebird returned to nest in any of many 2 dz houses. Didn't see or hear one nor on my 100 ml from home to hobby land. This year is looking the same. Is it bird flu? Or mass die off where our birds winter? Heard something about a spring storm during migration last year but could that eliminate that many? Raising a lot of tree swallows now.

nothing wrong with tree swallows, in fact I prefer than over bluebirds.

I have 2 houses with bluebirds, that is more than normal for me, I have 9 house now, added 3 more last year in a different field.
Always had 1 in 6 houses, usually one of the houses had tree swallows.

Population in my part of WI seems the same based on my small sample.

Experts will likely blame global warming. Science has gotten so much easier now that you don't have to show any actual temperature data, correlation between species abundance and temperature thresholds, or other possible hypothesis. Just blame GW for everything and move on.

North American songbird populations have been in decline for a long time. Habitat loss is usually fingered. House cats, windows, pesticides etc etc all play a role no doubt.

Not to mention the huge number killed by those environmentally friendly wind mills

They are hiding somewhere with the wolves that disappeared over the winter.

My houses are all occupied

WS

The main house is adjoining a country club and they have many boxes out as do I for blues… all look occupied.

Osky

I have 52 houses on my property, mostly for tree swallows with one usually occupied by bluebirds. Did my normal annual repair, clean, replace and or repaint last fall so everything should have been normal. This setup is about 20 years old now and I have had full occupancy for many years, often returning adults reclaim their previous nest accompanied by one or two yearlings who then have to find their own spot. This year I have just three pairs of tree swallows. It seems late for returns now and I am also worried about huge loss of birds.

The bluebird of happiness has left Minnesota.

I have never had blue birds here but I have seen by far a bigger variety of birds this year than ever before.

My buddy shot 3 house sparrows that were trying to use a box in his yard...a day later the bluebirds claimed it