Superb starlings are one of the more familiar birds in Kenya. From the Mara to the Rift Valley to the Ethiopian border, superb starlings can be found in a range of habitats across the country. Yet, despite how common they are, most people do not realize that they have one of the most complicated and sophisticated lifestyles of any bird in the world. Superb starlings form complex social groups—typically of around 25-30 birds—with multiple breeding pairs and are cooperative breeders, meaning a large number of non-breeding helpersaid in providing for offspring and nest defense.
It quickly became apparent that inter-annual rainfall variation was the key factor that influenced nearly all facets of superb starling physiology (how their body functions) and social behavior. Over the years, we have shown that year-to-year variation in dry season rainfall is directly related to levels of stress hormones, levels of reproductive conflict within groups, whether individuals try to breed on their own or help their relatives raise their young, and ultimately their survival and reproductive success . Just as interannual variation in rainfall influences stress physiology of starlings living in savannas, it also influences body condition, immune function, and overall health. We even find that conditions during early life affect behavioral roles later in life, possibly by influencing patterns of DNA methylation in the genome.
Over the years, our work on superb starlings at Mpala has expanded to other, closely related species of starlings that co-occur but have very different social systems. We have studied both the Hildebrandt’s starling, an occasional cooperative breeder, and the greater blue-eared glossy starling, a non-cooperative breeder. Similarly, we have expanded our study of superb starlings beyond Mpala’s borders to populations in the deserts to the north, the slopes of Mt. Kenya, and the grasslands to the south. By comparing the hormone physiology, DNA structure, and patterns of gene expression of populations across a country-wide ecological distribution, we have gained a better understanding of the physiological and molecular adaptations that birds use to cope with environmental change.
Most recently, we have been studying the characteristic iridescent plumage of starlings. There are four ways that birds produce iridescent feathers, but African starlings are unique because they are the only group of birds in which related species use one of the four ways to produce their bright plumage but possess all four types of ways. For this reason, they make a nice comparative system to study both evolutionary processes and developmental mechanisms of iridescence. We have shown how the production of new iridescent colors has led to the explosion of new starling species, and we now hope to explore whether these different color producing mechanisms are the result of novel gene combinations and developmental processes.
After nearly 25 years of continuous study we have not only scratched the surface of the complex lives of superb starlings, but we have only just been able to answer the original questions that led to the start of this project. With decades of genetic, behavioral, and reproductive data from the Mpala population, we now know that superb starlings are forming tight-knit family groups like most other cooperatively breeding birds. Instead, they are forming larger groups with variable kin structure that result from the influx of immigrant birds. Because starvation and predation at the nest is so high on the savanna, immigrants are essential to preventing groups from going extinct in the face of the constant threat of failed rains. This leads to the formation of large, mixed-kin societies, with multiple reproductive pairs that are able to persist for decades in the face of environmental fluctuation.
Ultimately, we are gaining critical information about how climatic variation and environmental change influence the behavior, physiology, morphology (how they communicate), and genetic structure of superb starlings. Only through long-term studies like this one can we begin to understand the lifestyle of these complex birds.