Imagery of dead birds can have several different meanings in a variety of cultures, but the most common application is symbolic of a loss of freedom. Due to the fact that birds are not Earth-bound like humans, they tend to represent freedom in literature, poetry and art. Therefore, dead birds often represent a loss of freedom, imprisonment or paralysis.
Other meanings are also possible depending on the variety of symbolic associations with different bird types. For instance, a dove is a representation of peace, so writing or art that depicts a dead dove is evocative of an outbreak of war or other situation of civil unrest.
For birds that represent particular ideologies, combining death with that imagery could symbolize the opposite meaning. For instance, the national bird of the United States is the bald eagle which often represents freedom and strength in this context. Therefore, a dead bald eagle is symbolic of the downfall of the American Empire or another anti-American sentiment.
Because storks are often depicted as bearers of life and associated with maternity, a dead stork is symbolic of a failed pregnancy or infant mortality.
In mafia circles, witnesses who testify against mobsters are often referred to as "stool pigeons" or said to "sing like canaries." Therefore, a dead pigeon or canary is used as a threat against those who consider testifying in court.