waw awesome birds !!

-WARNING- NERD CONTENT
The Gastornis and Titanis seem like perfect rivals as far as large extinct birds, at least to me. For example, though they look similar, to call the Gastornis a 'terror bird' would be a mistake. The family of fossil critters colloquially known as 'terror birds' is more scientifically known as Phorusrhacidae.(No, I'm not sure how to pronounce that) The Gastornis is unique enough to get it's own family, with the creative name Gastornithidae.
Phorusrhacids love to steal the thunder from other large extinct birds. Not only is it a more diverse family, but Titanis specifically is pretty significant. It's the only terror bird found in North America, and the claws on its flightless wings make it quirky. It's also popularly thought that Gastornis was not carnivorous, which peeves me slightly, though they'll be my favorite fossil critter whether they ate almonds or Eohippus. So, Titanis has some reason to get co.cky around them.
To put the cherry on top, the location the fossils were discovered indicate a possible culture clash! Gastornis fossils are primarily found in Western Europe, (Britain, France, Belgium, and Germany) while as mentioned, Titanis is North American, specifically Floridian. I took the creative liberty of giving both Gastornises British accents and dialects. (to the delight of my crazy skunk friend)
LET THE GAMES BEGIN!

Ah, now I remember! Titanis (or however you spell it) was believed to have odd looking claws on it's wings. If memory serves right, it was one of the largest of all terror-birds. Interesting choice for coloration!

^ Oops! Looks like my comment was late.... Anyways, it is somewhat odd that some scientists are pushing for the idea that some large prehistoric creatures (andrewsarcus, tyranasaurs, terror-birds, and so on) were not predators but rather scavengers and herbivores. It could be that these scientists want to make a name for themselves by challenging what we already know, like those post-modern theorists who claim that Einstein's theories are wrong. Your reasons behind the rivalry are very well thought out, it is interesting how some prehistoric spechies steal the spot-light from others (you'll see thousands of books on dinosaurs but hardly any on the creatures of the Permian era).

Oh the irony... XD