As the season turns to summer, you can see many parents carrying material for their nests or food in their beaks. They will be busy building the nests, caring for the eggs and eventually taking care of and educating the little ones. Unless there is a very good reason, humans should not disturb a nest. As you observe birds during the mating season, you will notice that some mates live apart from their groups while others stay in groups. The great tit and the Japanese robin are of the former persuasion, protecting and moving within their own territory, preventing other birds from invading.
Birds sing to warn intruders to keep out, and when such diplomacy fails, they fight.
The Japanese gull, little tern, and little egret fall into the latter group, and will live in an enclave of from scores to thousands of birds depending on the species. Invasion of territory so well protected is rare. This large breeding area is called a colony. In such colonies, it is easy to observe birds feeding chicks and demonstrating courtship. Whether birds stay in pairs or in mass groups sometimes depends on the place and the menu.