Based on part two of Trifles, the symbolism of the dead bird implies that Mr. Wright

Jealous because his wife paid attention to the bird. Jealous is showing suspicion of someone's unfaithfulness in a relationship. It pertains to the thoughts or feelings of insecurity, fear, concern, status or something of great personal value, particularly in reference to a comparator.

The symbolism of the dead bird implies that Mr. Wright had an oppressive demeanor that killed the bird and his wife’s spirit.

Explanation:

The bird symbolizes his partner being at bay - the bird lives in a very cage, unable to depart, a bit like Mrs. Wright is at bay in a exceeding wedding with an oppressive husband she cannot break loose. once the bird is killed, it symbolizes that Mrs. Wright's freedom is killed forever.