I went down a bit of a rabbit hole this morning studying male reactions to becoming fathers, and I found this article that cites a study that states that males who have higher testosterone are more likely to become fathers, but after all males studied became fathers their T-levels dropped sharply though temporarily.
They study authors concluded that the drop is caused by the need to adjust: "having a newborn baby require many emotional, psychological and physical adjustments"...
... but they push that this "could indicate an anticipatory psychological component to men's T decline around the time of birth of their children"
Then they state that their results are consistent with another study of multiple bird species that show drops in T-levels for fathers that help raise their young.
I checked that study about birds, and they state, "polygynous males appear less responsive to social environmental cues than are monogamous males"
