What is the importance of the bird to the overall action and tone of Susan Glaspell’s "Trifles"?

The little canary is a trifle whose significance is only
known by the women because they do not share its discovery with the men. In a sense, the
canary symbolizes Mrs. Wright (the former Minnie Foster). She is a woman married to an
abusive man who has sucked all the joy out of life for her. It is intimated in the story
that Mr. Wright most likely killed the canary by wringing its neck. It probably annoyed
this severe, abusive man with its singing. His wife used to enjoy singing, before she
married him. The reader must assume many things in this story, one of which is that Mr.
Wright killed the canary and that was the final blow for his wife. She wrung his neck in
the same way that he wrung the neck of her little canary. If the women had disclosed
that they had discovered the canary, this "trifle", no doubt it would have provided
further evidence that Mrs. Wright killed her husband. Without the canary, the men can
just assume that the cat ate it, and not have any further proof to condemn Mrs. Wright
for her husband's murder. They believe what the women tell them about the cat probably
getting the canary because, after all, what do women know? They are so concerned with
trifles.

The existence of the bird adds a lot of irony to
the story. It is a mere trifle that, if discovered by the all-knowing, important men,
could really clinch the case against Mrs. Wright. By not revealing the existence of the
canary, the women prove that they are more in control of things than the men give them
credit for. The canary also justifies, in a sense, the reason for Mrs. Wright strangling
her husband, so there is a sense of justice in the end.