A few years back I did a scientific study *insert gagging smiley here* on how Greenwing macaws evolve into 'bats'.
For those of you who missed my scientific article

...here it is again...
They start out so cute...
After a few months, they still seem okay...
They even play with other birds when they are young...
Even at a year old, they still appear 'normal'...
Then they start climbing on ropes...and hanging upside down at times...
And then one day for no apparent reason, they turn into bats...
