Humans may complain but they, too, won’t judge the bird for being inappropriate. It’s a bird being a bird. Birds do all kinds of things, such as dirty up one’s newly washed car as they fly by. Yet it is appropriate for the bird to behave in that way.
But when we get to human society, we have all kinds of behavior codes that enable us to get along with our particular society. They may not be based on whims and opinions but they are based on consensus, regardless on how that is reached. Sometimes it is by who is the strongest and carries the biggest stick. Other times it is because it is truly more convenient for all. Someone screaming all night long is not appropriate because it is waking everyone up in the vicinity, destroying everyone’s natural right to a good night’s sleep.
Buying a child bride with livestock is one example of behavior that is encouraged and highly regarded in some societies. In others, it is considered child abuse and totally bad behavior. It all depends on how we were conditioned as children to fit into our society and gain its love and support. We are powerless as children to change any of this and will be punished if we try. These rules were made by people bigger than us.
Even the smallest and most basic behavioral patterns, such as sneezing is determined by our immediate society and how we are brought up by those around us. To fit into certain echelons of society, a person should sneeze softly or inaudibly into a tissue. Others sneeze percussively into the open air, because that is all they saw when they were growing up. From a public health point of view the former is better. But from a behavioral point of view the latter is more acceptable in that person’s social sphere. They would seem ridiculous, daintily sneezing into a tissue, especially if that society does not have access to them.
So, though not necessarily based on whim and subjectivity, correct behavior is based on agreements we make to be part of our society. If we don’t follow these codes, we will be ostracized, punished, shamed, scoffed at, imprisoned, committed to an institution, or even killed. These are pretty good reasons for why many hideous behavior patterns, such as genocide, inquisitions, suppression of women, and war have persisted throughout the history of humans. And they are also good reasons for why people behave within certain norms.
Our parents, teachers, and peers, teach us what constitutes correct behavior. This can also be a good thing. We need to know how to behave in public so as not to infringe on others’ rights to be left alone and in peace. If I am on a crowded subway car and someone gropes me, this is not acceptable behavior. He has not been able to control his impulses. We are taught in this society that it is not ever good to “reach out and touch someone” that you don’t know and and has not invited you to do so.
As in so many structures in life, our behavioral codes serve human society at large. They have evolved to make sure a culture is on the same page. This can be both good and bad insofar as how much pain and suffering they bring or how much order and peaceful co-existence results.