This resolves to Vox Future Perfect's judgement of this question.

2022 was the worst year ever for avian flu in the US. The outbreak tore through giant chicken and turkey factory farms throughout the country, resulting in the mass extermination (using, it’s worth emphasizing, the cruelest kill method imaginable) of more than 57 million birds. Last year, Future Perfect predicted that 2023 bird flu deaths would again exceed 50 million, which didn’t quite come true. As of this writing (December 21), only about 19 million poultry birds have been culled in 2023, bringing the total from the bird flu outbreak that began in 2022 to about 77 million.

Nearly all of those 2023 killings took place in the last couple months of the year, which means that we’re currently in a big resurgence of the disease (consistent with its seasonal transmission pattern). The number of birds culled between October and the end of 2023 was more than double the number from the same period the previous year, which tells me avian flu is heavily ramping up right now rather than slowing down, as it was in late 2022. But the flow of animal diseases can be pretty surprising, so with all that in mind, I predict with medium confidence that by the end of this year, the 2024 death toll from bird flu will exceed 20 million. —MB

Vox's prediction was "60 percent"