The birds are all living normally in the ecosystem and the two birds in the back are quite hungry.
The birds with red and white heads were eaten causing only the birds that better blended in the trees to survive.
The bigger birds migrated away leaving on the smaller birds in this current environments ecosystem.
It started raining and only the smallest bird could fit inside the tree getting shelter. And The bigger birds have migrated back and they are very hungry. Along with the rain it makes the birds easier to see therefore the bigger birds can eat them.
The bigger birds landed on the smaller birds and managed to eat them. After this meal the rain stopped and they traveled away to another forest.
The smallest bird survived meaning that he can go on and reproduce later in life.