The effect of low nesting density caused by the fragmentation of nesting biotopes due to seasonal flooding on the development of aggressive behavior and on growth of black-headed gull chicks was investigated. An analysis of the behavior of birds nesting with different densities showed that contacts with neighboring broods were less frequent in chicks from more sparsely distributed nests, while aggressive behavior could be observed in these broods earlier and more often than in their peers from the nests located in more densely populated areas. By testing the parent birds using a standard stimulus of territorial behavior—a remotely controlled stuffed gull—we found that the hosts of widely spaced nests reacted more aggressively but left the clutches less frequently than their neighbors that nested more densely. On average, the chicks from the sparsely distributed broods grew faster and the daily increment of the skull size of the chicks correlated inversely with the frequency of parental visits. We suppose that in the case of the seasonal decrease of nesting grounds, the offspring of more aggressive young couples nesting in the most sparsely populated areas had an advantage in the development probably due to the maternal influence on the composition of the eggs. According to our data, in the conditions of low-density nesting, the parental influence on the growth of chicks and development of their aggressive behavior prevailed over the possible developing effect of the social experience.