Why? Because plants and other species - life in all its variety - has been here a lot longer than we have.
Species come and go - more than 90% of all the species that have ever existed may be gone ( trilobites, dinosaurs, etc.),
without our interference.
I like to feed the birds - but I don't worry about them collectively. Life adapts and moves on.
see:
http://www.rense.com/general57/ew.htm
metatron