Bermudian bluebirds are at greater risk of dying out than their American cousins, according to a recent report.

The study, “Island Life Shapes the Physiology and Life History of Eastern Bluebirds (Sialia sialis),” compared the Eastern bluebird population in Bermuda to that in Ohio. While it found that bluebirds had similar clutch sizes and hatch rates in both areas, the chicks in Bermuda were less likely to survive to adulthood, particularly later in their breeding season.

Researcher Dr Kevin Matson wrote: “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.”

In addition to the bird’s mortality rate, the study also noted some physical differences in the bird populations, with Bermudian bluebirds being generally lighter and with longer wings than their equivalents in the US.

He said that in order to protect the species on the Island, conservation planners should look at the nesting mortality, along with the survival rates of birds of all ages.

Dr Matson added that conservation planners must consider the consequences of introduced predators and competitors and their possible removal, along with any man-driven changes in the population of insects bluebirds eat and feed to their chicks.

“These factors may not only affect survival and mortality rates but may also shape bluebird physiology and reproduction,” he said. “Ultimately, our study highlights the value of considering the match between an organism, its environment, and its evolutionary history on a population-specific scale. Without this context, identifying detrimental trends is a more challenging proposition.”

The study was published by the University of Chicago Press in the January/February edition of Physiological and Biochemical Zoology.