Researchers Discover Four New Mite Species Living Inside Ibis and Spoonbill Feathers
By Meredith Swett Walker
If you were to page through a field guide to birds searching for species that look as if they were dreamed up by Dr. Seuss, you’d probably choose some from the family Threskiornithidae, which includes ibises and spoonbills. For instance, the Eurasian spoonbill, a leggy bird that looks like it has a long-handled spoon protruding from its face. Or the Southern bald ibis, which sports a somewhat less bizarre bill, but a pale, featherless head topped by a fleshy, red “beret.”
So it should not be a surprise that on these fantastical birds, we should find other Seussian characters — minute quill mites that recall the tiny “Whos” in the children’s classic Horton Hears a Who. Rather than residing on a speck of dust, these mites spend their entire lives inside the hollow quill of a bird feather. In the latest issue of the Journal of Medical Entomology, Dr. Maciej Skoracki of Adam Mickiewicz University in Poland and his colleagues describe four new species of syringophilid quill mites in the genus Stibarokris. This is the first documentation of syringophilid quill mites infesting ibises and spoonbills.
Unlike Seuss’s charming “Whos,” these mites are parasites. They poke their syringe-like mouthparts through the tough wall of the feather quill and into their host’s skin. This allows them to sip the host’s fluids without ever leaving the feather. Surprisingly, there is limited evidence that the quill mites cause much damage to feathers or irritation to their hosts. However, Skoracki notes that recent studies have shown that syringophilid mites may be vectors for the bacterium Anaplasma phagocytophilum, a pathogen that can cause symptoms that are similar to Lyme disease.
Only female mites leave the interior of the quill to disperse to new feathers, or perhaps another bird that is in close contact with the host — for instance, a nestling or mate. This restricted dispersal is associated with high host specificity — about two-thirds of the known species of quill mites are only associated with one species of bird.
The discovery of Stibarokris species infesting birds in the family Threskiornithidae gives scientists clues as to the evolution of this genus of mites. Threskiornithidae is divided into two groups, or clades. One clade is found only in North and South America, and the other clade is associated with Africa, Europe and Asia. It is believed these clades diverged when the ancient supercontinent of Gondwana split into South America and Africa (as well as another supercontinent East Gondwana.)
Skoracki and colleagues found the new Stibarokris mites on bird species in both Old World and New World clades, which suggests that this genus started parasitizing birds in the Threskiornithidae family before the clades split. Scientists believe this split occurred 38-41 million years ago, which would make the mite genus Stibarokris even older than that. Morphological traits of mites in this genus also suggest that Stibarokris may be one of the oldest genera of syringophilid mites.
So far, syringophilid mites have been found in more than 480 species of birds across 24 of the 30 orders of birds. And most species of mites in this family were first described only very recently.
“Previously, nobody had the idea to look inside feather quills of these birds,” said Skoracki. “In my opinion, the great biodiversity of many mite groups, including quill mites, is still undiscovered.”
If the tiny mites of the genus Stibarokris are the “Whos” of our Dr. Seuss metaphor, that would make Dr. Skoracki “Horton.” When Horton the elephant gets to know the miniscule “Whos,” he declares, “a person’s a person, no matter how small.” In our case, Dr. Skoracki and his colleagues have tapped into a rich vein of biodiversity and discovered “a species is a species, no matter how small.”
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Meredith Swett Walker is a former avian endocrinologist who now studies the development and behavior of two juvenile humans in the high desert of western Colorado. When she is not handling her research subjects, she writes about science and nature. You can read her work on her blogs http://picahudsonia.com and https://citizenbiologist.com or follow her on Twitter at @mswettwalker.