The five species of warbler migrate out of the coniferous forest through the deciduous forest and cultivated land in eastern North America and, mostly, into the West Indies and Central and South America. Therefore, any behavioral characteristics that remain the same throughout the year must be nearly independent of the specific
environment (at least within the range of environmental variation to which the bird is normally exposed). If any aspects of the breeding season behavior are retained throughout the year, these would be expected to be more fundamental than those aspects that varied with the local environment. This would be especially likely if the
retained aspects of the behavior were controlled by morphological characteristics. The varying aspects would be interpreted as the result of interaction between the fundamental characteristics and the environment, as direct results of stimuliparticular to that environment, or as seasonal aspects of birds' physiology. Thus it is of interest
to compare behavior in different seasons.