My sister just called me with a similar problem with the phoebe nest on her deck. The first thing that came to my mind was the cowbird. I'm surprised that no one has mentioned this notorious brood parasite. Even though the cowbirds most common host is the yellow warbler, the brown-headed cowbird often targets Eastern phoebes for its host. I've actually seen female cowbirds egg-dump phoebe nests. It's an extremely fast process. Now before people have evil thoughts towards the brown-headed cowbird, I have to say this: it's not the cowbirds fault... Cowbirds evolved following roaming buffalo herds around, and therefore developed a breeding strategy (brood parasitism) that allowed them to do so. The cowbird used to be an uncommon species here in the northeast, but during the 17 and 1800s almost all forests were cut down for farmland. Since cowbirds are an open spaces/prairie species, this is the perfect habitat for them. They also like edge habitat (powerlines, forest edges etc.) So, I told my sister to keep watching the nest for a cowbird chick. The young, a week or two along, should be larger, louder and healthier by far than the others. It's more agressive behavior as a nestling makes it sure that it gets fed at the expense (often fatal) of the others. So if the young in a nest all look and sound the same, chances are it "cowbird-free."

Just an idea... When they're done nesting for the season, you could put something on the speaker that would discourage them, and put up a little shelf or ledge that they could use next season?

My phoebes had skipped a year of nesting in their usual place (above the porch light fixture near my office door). My mirror set-up had scared them away. I should have realized that birds do not "like" mirrors -- but I didn't think about it at the time. I did see a bird pecking all day at the mirror, looking behind it, then pecking angrily at it when seeing the "intruder" again. That bird came back the next day to peck at the mirror again. I felt sorry for him wasting his time. But, I didn't think about the phoebes reaction being the same. So, they never nested there last year. I removed the mirror, but they still did not return to nest there this spring. Instead, they nested on another side of the house -- under our raised deck (same as last year). But, after the 1st brood was fledged -- THEY MOVED BACK TO THEIR OLD NESTING SPOT! So, the phoebes apparently got fed up with the disturbances created by our toy poodle (who is let out onto our raised deck several times a day.) The poodle would be walking directly over their nest, and possibly pissing over their nest. The nest building started May 25, 2021 and completed on the 30th or 31st. The mother was sitting on the nest on May 31, and there were 2 eggs in the nest. So, the first egg was likely delivered on May 30. By June 3, there were 5 eggs. All the eggs hatched on June 17 -- so, exactly 2 weeks after the last egg was laid. Interesting that all eggs hatched on the same day, even though each egg was laid a day apart. When I peeked, all the shells were gone. So, even tho I didn't see it, I assume that the parents removed all the egg shells. I also see the parents flying away with baby-bird poop. The poop looks like worms, and the parents carry it away from the nest. They either drop it or eat it (it is undigested food). Today is June 23, and the parents are often very busy bringing food. The bay birds are still too small to see without using a mirror over the nest. Here is a link to a very interesting article from 1937, detailing the observations of nesting habits of phoebes as studied over a 3-yr period. A few interesting details: Female does all the nest building. Incubation starts at varying times - sometimes after 3rd egg, sometimes after 4th, sometimes after 5th. The male apparently does none of the incubation. After fledging, the young birds remain close to the nest, getting farther way as the days pass. Both parents still feed the young after they fledge -- feeding them for periods of up to 18 days. Reliance on the parents gradually decreases. The parents may eventually show harsh treatment of the young to get them to go out on their own. Interesting. https://sora.unm.edu/sites/default/files/journals/auk/v059n03/p0410-p0417.pdf

We had the exact same problem on our back porch with nesting Phoebes. We determined that the 1st babies and nest was infested with tiny bird mites. We removed the nest and tried to use diatomaceous earth in 2nd nest but the 2nd brood didn't make it. Very sad. I wish i know how to kill the mites.