Once upon a time, there was a bird called Aves Veneno. It had a sharp beak and talons, and a pointy venemous tail. It made big nests in trees, ate small birds, and drank water and the blood of other animals
One day, a forest fire burned the trees where it lived down. There was also a drought, so there was less food and water. Finally, there were many more boys born than girls, so not everyone could find a mate.
To adapt to this, they started making their homes on the ground in caves, where it was big and safe.
Many of the animals it ate became rare to see because most died in the fire, so they developed bigger beaks, talons, and wings. They also made their tail more deadly. Now they would have no problem catching a meal when they saw one.
They also evolved to absorb iron better, so they could drink more blood. They had to do that because all the water dried up. Besides that, they started travelling in big groups of both boys and girls, so boys could find girls (mates) easily and also be with them more.
When the water and trees returned, Aves Veneno had to adapt again. Some went back to the trees, and some stayed on the ground. The ones in the trees kept some traits like the bigger beak, talons, and wings, as well as the deadlier tail, but didn't keep others like living in larger groups or being able to drink more blood. Over time, they changed more and more, until they were both entirely different species. The End.