Odor as a defensive weapon - for skunks and plants

Everybody knows that skunks can spray a liquid with a strong odor as a defensive weapon. 

Trees can protect themselves with odors as well - but in the opposite way. When they are attackad by insects biting into the leaves, trees emit odors
into the air to attract birds and bees (more exactly carnivorous wasps). 

Remember the scent of a freshly mowed lawn? Or torn leaves?  Similar scents attract various species of birds and insects - depending on the plant and the kind of damage.

In the recent paper, scientists released chickadee-like birds in an orchard of apple trees. Most birds immediately flew to trees infested with caterpillars.
Even if the birds could smell but not see.



REFERENCE

Luisa Amo1,2,*, Jeroen J. Jansen3, Nicole M. van Dam4, Marcel Dicke5, Marcel E. Visser1  Birds exploit herbivore-induced plant volatiles to locate herbivorous prey  Ecology Letters (2013) 16: 1348–1355