Forerunner fauna and flora
From Halopedia, the Halo wiki
Fauna
Land Animals
Halo Dinosaurs are native lifeforms to Halo, possibly only on Installation 04. They are both bipedal and quadruped in stature, and somewhat resemble Earth's dinosaurs.[1] The larger animals' names are known as Thorn Beasts, the smaller one has been identified as a Blind Wolf.[2]
Although they did not make it to the final cut of the game, this does not exclude them from Halo as a whole. For example, Engineers didn't make the final cut for Halo either, but they were depicted in the Halo Novels. So who knows if these animals are meant to be there, but just unseen. They seem to have been created to add some more depth to the Halo Myths.
The Dino-Birds
(Main Article: Dino-Birds
On the levels, Delta Halo, Regret, Gravemind and High Charity, there are birds flying around in the sky. They are also in the Halo 3 multiplayer maps Guardian and Epitaph where they can be examined more closley by Flycam in Theater or 343 in Forge. At first they seem like dinosaurs, but they are seen in High Charity, so it is also possible that the Covenant brought "food," and they are seen on 05 because they would breed quickly. But then, if they are dinosaurs, the Covenant might bring specimens to their holy city. It may never be known if they are dinosaurs, or wildlife brought by the Covenant to use as hunting game, this could be confirmed by the existance of the supply ship complete with a hunting preserve, Infinite Succor from the Halo Graphic Novel. Bungie may very well be the only ones to ever know.
Also, since we know that Halo contains a vast multitude of terrains and environments, much like Earth, it is possible that life has been developing on Halo over the 100,000 years that they have been dormant, such animals like the dino birds. Another reason why animals may NOT be seen is because they have the calcium store necessary for the Flood to infect, so the animals may have been destroyed by the guardians of the construct, and only avian-like animals survive since it was mentioned that Jackals do not have sufficient calcium mass to sustain the Flood.
In Halo 2 and 3 these "birds" can be shot and killed; they are difficult to hit and, after being killed, they turn into a splatter of red blood.
It is highly likely that there is no real animal life on the Halo Installations because the monitors used them as food for the Flood so they could further study them. The birds could be too hard to obtain for the forerunners and/or their bodies' do not contain enough calcium for the Flood to feed off of.
Moths
Seen in 343 Guilty Spark.
These moth-like creatures were only ever seen in the dark errie tensionate swamps of 343 Guilty Spark. They were the only animals ever seen on Halo, except for some animal calls.
Other
Animal calls were seen in 343 Guilty Spark along with the moths. One of the most common sounds were a Owl, however there were some cricket sounds.
Sea Worms
Silent Cartographer
These sea worms floated harmlessly on the surface of the water.
Flora
(Means Plants)
Flood Stalk Plants
Seen in: Backwash, 343 Guilty Spark, and Gravemind and High Charity.
Forerunner Trees
Seen in: Halo, and Assault on the Control Room
Bushes
Seen in: Halo
Sources
High Charity (Level) 343 Guilty Spark (Level) Regret (Level)
