They were known to take dives into the water as deep as 1km.
Are you sure about this? 1km is very very deep, damn birds were almost submarines, it's a shame so many species become exctint because of humans...
I sometimes wonder if new species are evolving to better deal with humans or if evolution isn't fast enough to deal with the level of destruction we do to the environment...
Just like I wrote , they were not really studied by scientists when in existence, their behavioral pattern were inferred from descriptions based on layman's account, it's a shame they are lost as we will not know more about them, I just hope we do better at conserving the endangered in our midst .