The behavior, physiology, and morphology of individual Eastern Bluebirds vary in response to ecological and social circumstances. Because comparative studies of breeding biology and behavior have revealed that individuals vary in condition-dependent ways, populations of Eastern Bluebirds may be appropriate models for further study of facultative expression of behavior and physiology, as first noted by Musselman (Musselman 1946).
Links between vocal communication and behavior in Eastern Bluebirds still remain obscure, despite interesting documentation of the remarkable variation in vocalizations of local males (Huntsman 2002). A study of vocal communication of males, females, and juveniles across the range of the species would be useful and interesting. Careful previous studies (Krieg 1965, Pinkowski 1971b) provide background for future studies of variation in vocal communication as a function of variation in social behavior (well studied). Similarly, knowledge of migratory behavior and physiology is sparse, although studies of hormones and behavior of wild-living bluebirds are more common now than in the past.
In contrast to the detailed knowledge of variation in social behavior, development during the fledgling period is hardly described. Nor are movements of birds in juvenile plumage yet studied. Such studies would have significance for understanding dispersal outcomes and the proximate ecological and social causes of natal dispersal. Although there are some studies on breeding dispersal, more information on additional populations likely would provide insight into the contingencies of the lives of adult individuals.
Eastern Bluebird populations vary in terms of whether they are above or below replacement levels. This variation, along with networks of bluebird trails that cover eastern North America, make the species a model system for a rangewide study of source-sink population dynamics (Pulliam 1988). Similarly, little is yet reported of the demography of populations of bluebirds.
Seasonal movements and migrations are yet to be systematically studied, except for the data generated by the Bird Banding Laboratory. These data turn out to be sparse compared to the detail of telemetry studies. As telemeter technology gets smaller and more affordable, studies of the movements of individual bluebirds will likely yield surprises.
Variation in nestling sex ratios across the range of this species suggests that continued, detailed study of sex ratio variation in populations of Eastern, Western, and Mountain bluebirds has a high probability of rewarding observers with insight into the adaptive significance of sex ratio variation. Ecologically dependent sibling competition is suggested by differences in nestling behavior between mainland and Bermuda populations, and in statistically significant differences in breeding parameters of neighboring Piedmont populations in Georgia and South Carolina.
Eastern Bluebirds are ideal species for studying the effects of environmental contaminants on behavior and reproductive success. How common is endocrine disruption in bluebirds from typical exposures to pesticides, herbicides, fertilizers, pollution from household cleaners, cosmetics, and poisons? Students interested in the epidemiology of endocrine disruption in wild-living animals should consider studying the endocrine disrupting and other health effects of exposure to common petrochemicals, such as glyphosates.