John C. Mittermeier / 2 Oct 2024 / Unicolored Thrush
The Unicolored Thrush won’t grab your attention with flashy colors or an exciting name, but what it lacks in plumage pattern it makes up for in rarity and intrigue. Endemic to the lowlands of northern Bolivia, this unusual bird is so difficult to find and so poorly-known that even long-time birders in the region were starting to doubt whether it existed as a species at all.
As of August 2024, there was only one photograph of the Unicolored Thrush in eBird, an image taken in 2011, along with a small handful of sound recordings on xeno-canto.
Behavior and identification challenges have both contributed to the lack of records. Within its limited distribution, Unicolored Thrushes appear to specialize in seasonally flooded forests along rivers. The birds may nest and do most of their singing during the rainy season when the water levels are at their highest and accessing the proper habitat to look for the bird is nearly impossible. Add to this the fact that the thrushes are notoriously shy and have no conspicuous markings to confirm their identity, and it starts to become clear how the Unicolored Thrush became a lost bird.
Tini and Jacob Wijpkema have lived in Bolivia for more than 10 years, after moving there from the Netherlands, and dedicate much of their time to searching for and studying birds across the country. In the past decade, they have seen an incredible 1,309 bird species in Bolivia. This has included spending considerable amounts of time birding in Unicolored Thrush habitat, but never once had they actually seen one of the thrushes. After so little success, Jacob was starting to doubt if the Unicolored Thrush existed at all.
That changed on August 14, 2024, when Tini and Jacob found an unusual, plain brown thrush in one of their mist-nets while they were doing a research project at Chuchini Ecological Reserve, a private nature reserve near the town of Trinidad in El Beni department, Bolivia. As soon as they saw the bird, Tini and Jacob suspected it was a Unicolored Thrush, and quickly shared their photographs with friends and colleagues to confirm the identification and share the good news.
“Having this bird in my hands,” says Jacob, “one of the things I was most happy about was confirming for myself that the species really existed!”
Other experts had faced similar doubts about the thrush.
“After searching for Unicolored Thrush several times myself no luck, I had also started to wonder whether it was a real species, particularly since another species, Hauxwell’s Thrush, can look very similar and is common in the same region,” says Joe Tobias, a professor at Imperial College who authored one of the first papers on lost birds in the Americas, and helped Tini and Jacob confirm the identification. “There have been a few sightings and sound recordings in recent years but this series of photographs by Jacob and Tini of a mist-netted individual is the best evidence that the Unicolored Thrush continues to survive even close to the town of Trinidad.”
The last documented records of Unicolored Thrush that the Search for Lost Birds knows of are sound recordings on xeno-canto that Dan Lane made in September of 2013. These are part of a series of recordings of the species that were made by Dan and Frank Rheindt between 2010 and 2013. There were a number of sightings of the species in the intervening years, for example by Sebastian Herzog in 2015 and again by Dan Lane in 2016, but none of these more recent observations included opportunities to photograph or sound record the species. We added Unicolored Thrush to the most recent update of the Lost Birds List in August 2024. Coincidentally, this turned out to be just two days before Tini and Jacob got their photographs!
Hopefully this new set of photographs encourages more people to continue finding and documenting this poorly-known species.
“The fact that Chuchini, where Tini and Jacob found the thrush, is a protected area is also good news,” says Joe, “and raises hopes that a population of this mysterious bird can be protected and studied.”
Unicolored Thrush is considered Near Threatened on the Red List of Threatened Species: https://datazone.birdlife.org/species/factsheet/unicolored-thrush-turdus-haplochrous
To learn more about Unicolored Thrush see the Birds of the World profile page for the species: https://birdsoftheworld.org/bow/species/unithr1/cur/introduction#hab