Study Highlights Differences in Mainland and Island Blue Bird Populations

An investigation of blue bird populations living in Ohio and on Bermuda has reveled marked differences in the populations despite their belonging to the same species.

Researchers from University of Groningen in the Netherlands report in the journal Physiological and Biochemical Zoology their examination of eastern blue birds (Sialia sialis) in Ohio and Bermuda from eggs to fully grown adults.

"We investigated how nestlings and adults differed in growth, size and shape, immune function, numbers of eggs and nestlings that pairs produce, and how frequently parents deliver food to their young," the study's lead author Kevin Maston said in a statement.

"We also attempted to identify differences between continental and island birds that, either individually or as part of a broader phenomenon, might intensify the risks of decline typically associated with small and geographically isolated populations, such as the Bermuda bluebirds," he added.

While blue bird populations in Ohio - which has an area of about 45,000 square miles - is thriving, that is not the case in Bermuda, which is only about 21 square miles. Blue birds in Bermuda are threatened with extinction.

"Our study showed that bluebirds in Bermuda differed in a variety of ways from bluebirds in Ohio," Maston said. "For example, adults in Bermuda were lighter weight and had longer wings than the Ohio birds. These differences contrast with the usual changes associated with small animals living on isolated islands. Parents fed their nestlings at equal rates throughout the season in both locations. However, island nestlings grew slower and, as the breeding season progressed, more chicks died in their nests in Bermuda, though no similar seasonal pattern was observed in Ohio."

"Overall, our results suggest that the Bermuda bluebirds may be adjusted to certain aspects of the island environment but not to others," Maston added.

Maston suggested the research could be used to improve conservation efforts of blue birds on Bermuda.

"Ultimately, our study highlights the value of considering the match between an organism, its environment, and its evolutionary history on a population-specific scale," he said. "Without this context, identifying detrimental trends is a more challenging proposition."