If a woodpecker wants a home, it does more than just knock on wood – it takes some tiny helpers with it. The red-cockaded woodpecker seems to carry spores of fungi that rot wood in what appears to be a symbiosis that benefits both partners.
Red-cockaded woodpeckers live in the pine forests of the south-eastern US. They have an important role as “ecosystem engineers”, digging tree cavities that they use for many years and that are then used by other species when they move out.
The birds live in family groups, and each group usually has several cavities at different stages of construction. It’s no quick bodge job – carving out the holes can take eight years.
Some people think that woodpeckers get help from fungi to make their cavities, but evidence for this has been lacking – until now.
What’s on your beak?
Michelle Jusino of the US Forest Service Center for Forest Mycology Research in Wisconsin and her colleagues have caught woodpeckers at a field site in North Carolina, swabbing their beaks, wings and feet.
The team found a wide range of fungal spores, including many that cause wood decay and are found in cavities that woodpeckers excavate.
To see whether the birds bring the fungi to their cavities, the team drilled holes through the sapwood into the heartwood in 60 trees near cavity clusters maintained by woodpeckers. Thirty of these cavities were covered with steel screens with openings too small for woodpeckers to get through.
After 26 months, the holes that were accessible to the birds had fungal communities living in them that were more similar to those found in natural woodpecker excavations than to the communities in the inaccessible holes. This suggests that woodpeckers do disperse fungi, but any benefit to the birds is still unproven.
Researchers would have to inoculate trees with different fungi and show that birds could excavate more readily in some than others. “Something like that would take many, many years, maybe a decade to test out,” says Jusino. “I would very much like to do it, but doing this kind of work in a field study is extraordinarily difficult.”
Shortage of homes
Red-cockaded woodpeckers are endangered in the US, and one of the factors limiting their population size is the need for a cavity for each individual. Conservation managers try to help out by drilling holes through sapwood to help them get started.
“For those particular birds to ever be independent of cavity management, we need to know what is limiting excavation and why,” says Jusino. “I didn’t necessarily expect to find this result but it’s very, very exciting. If our birds are shown to carry fungi, more than likely there are very many other birds that carry fungi.”
But Teresa Lorenz, an ornithologist at the University of Idaho in Moscow, says that while the study is important and well-designed, the findings shouldn’t be extrapolated to other woodpeckers. “Most woodpeckers I work with rapidly create a cavity, from start to completion within one week,” she says.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2016.0106
Article amended on 23 March 2016
Correction: Since this article was first published, the number of trees drilled into by Michelle Jusino’s team has been corrected.
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