The red-headed woodpecker has enjoyed better days. Over the past five decades, the species has suffered sharp declines in the northern and western parts of its range. While that much is clear, the role of their diets in the declines is not. A recent USDA Forest Service study observed the diets of nestling woodpeckers to aid with conservation efforts.
In addition to determining the main diet of the nestling red-headed woodpecker, the scientists also sought to examine variability in food types eaten over time and the roles of female and male woodpeckers in feeding their young. Their findings were published in Southeastern Naturalist.
The scientists chose the Savannah River Site, a Department of Energy site in South Carolina where a long-term study on coarse woody debris was already taking place. Vukovich and Kilgo used the established study plots concurrently for a larger study on red-headed woodpeckers.
From June to September in 2006 and 2007, the scientists observed what the woodpeckers ate. “I set up a spotting scope pretty close to the nests, usually 30 to 100 feet away. Sometimes I’d get in a blind so they couldn’t see me,” explains Vukovich. “I watched them, particularly during the later stages of their nests, when the adult woodpeckers would fly there and hold the food out for their young. This allowed me to identify the food.” While Vulkovich and other assistants couldn’t always identify the food exactly, they could usually tell whether it was plant or animal matter.
Answering the question of whether there’s a difference between what male and female adults feed their young took a little more work. Red-headed woodpeckers are monomorphic, meaning that the males and females are nearly physically identical. To bypass this hurdle, breast feathers taken from the captured birds that were sent to a lab that ran DNA to determine their sexes. Captured birds were uniquely marked with bands or fitted with a transmitter. The researchers identified the individual woodpecker at the nests and then could note what the respective sexes fed their young.
Throughout the duration of the study, 791 food items were recorded as being fed to nestling woodpeckers. The items included seven species of plants and 18 species of animals, with 16 being invertebrates – insects – and two being vertebrates. The scientists used statistical models to determine the proportions of animal matter versus plant matter consumed.
The scientists found that 71.5 percent of the nestling diet was animal matter and 28.5 percent was plant matter. “We were actually a little surprised at how much fruit they were feeding their young, since that’s believed to slow development,” says Vukovich. “More protein, such as from bugs and insects, is usually better for the development of nestling birds. However, there’s been research that suggests that some birds can handle fruity diets better than other birds.”
Vukovich and Kilgo didn’t find any significant difference between what the sexes fed their young, using statistical models. “Another important finding was that most of the variations in nestling diet we saw were related to annual and monthly effects. That means that changes in what foods were available across a year, or even across a month, influenced what the woodpeckers ate,” adds Vukovich.
The study fills a long-standing gap in academic literature. Prior to Vukovich and Kilgo’s study, most information about diets of red-headed woodpeckers comes from a USDA biological survey carried out more than a century ago, in 1911. That survey examined the stomach contents of woodpeckers, which could lead to an incomplete picture of their diets. The ages of the woodpeckers were also unknown, adding to the uncertainty.
Another, arguably more important aspect of the study is its implications for conservation, management, and further study. “There are still a lot of aspects of red-headed woodpecker ecology that haven’t been studied, which could contribute insights about their decline,” notes Vukovich. “Kilgo and I think that more knowledge related to how they use their summer habitats, particularly how they exploit food, could lead to targeted management to help with conservation efforts. Furthermore, this work may act as a catalyst for further research about how the woodpeckers use their habitats.”
For more information, email Mark Vukovich at firstname.lastname@example.org.