I wonder if they fly 60 mph coasting on near surface gusts like some small seabirds do or whether that is 60 mph at a higher altitude level flight. Judging by how low I have seen some bats fly getting from one place to the next over land, I imagine it might be the former but idk.

So the claim in the article is in the 4th paragraph

Hoary bats have been known to fly from the US mainland to Hawaii in about three days, at an average speed of 60 mph. Flying at speeds up to 100 mph, the Mexican free-tailed bat is the fastest bat in the world.

but happens before the main topic of the article which is

US Geological Survey researchers, who partnered with BCI on this research, have been studying bats along the US West Coast in the coastal and offshore environment. Offshore sites are typically deployed on coastal rock formations and islands, which are difficult to reach and maintain. They are focusing on migratory bat species like the hoary bat, the silver-haired bat, the western red bat, and the Mexican free-tailed bat.

and the article is mostly about a sail drone that passively collects data about the environment. The article discusses some data collection events around San Francisco, but doesn’t back up the initial claim of the premise of the factoid, as in the factoid isn’t derived from the main subject of the article. It is however, allowed to sit adjacent to the main subject of the article and is in some sense a kissing cousin; this is how false claims often find their way into ‘folk truth’, its a kind of bait-and-switch approach to rhetoric.

We do know at least once in the previous 1.4 million years, at least one pregnant female bat, or at least more than one ancestor of the Hawaiian hoary bat made it to the islands, so there is that. However, if Hoary bats, or any other bats were regularly making this journey, we would very much expect either more genetic diversity or far more species of bats across the islands, as there would be many introduction events. I can’t find any documentation about the original claim however, which I would label as unfounded/ false. We don’t actually know that the introduction event came from a bat flying, or if the bats arrived on a vegetation raft.

Digging in a little further leads to this article in the Maui news, which leads to this publication from the Parks service, which is a genomics analysis of the extant populations of the Hawaiian Hoary bat. The finding is that the Hawaiian populations came from a small number of dispersal events (3 most likely), 9k, and 900 years ago. It makes no suggestion of dispersal by air, and rafting is a know method of dispersal for many other terrestrial species of invertebrate in Hawaii. Again, only no/ weak evidence of this journey being done by flight. More than possible that the bats arrived after some massive flood on the west coast and they were trapped on vegetation rafts that washed ashore or came near enough for them to make landfall.

Wish that article had more information, it doesn’t really answer my questions unfortunately.

But thank you for the source!