Vocalizations of Willard's Sooty Boubou
Tom Gnoske, Josh Engel and I just returned from five weeks in the eastern Democratic Republic of Congo and Uganda. As part of our John D. Catherine T. MacArthur Foundation grant to investigate effects of climate change on genetic structure, we reached field sites along the Itombwe Plateau and in Kahuzi-Beiga National Park in the DRC. In both areas, we were on the look out for Willard's Sooty Boubou (Laniarius willardi), which we described in 2010 based on specimens Tom Gnoske, Ben Marks and Charles Kahindo first collected in Uganda more than 10 years ago. We did not find the bird in either one of the Congolese sites we visited, but that was not entirely a surprise. In both Itombwe and Kahuzi-Biega, we had to work in forests at 2100-2300m elevation. These elevations are inhabited by another black boubou, Mountain Sooty Boubou (Laniarius poensis). We found this species to be common at both sites. Forest below 2000m is essentially gone in both areas and that is where Willard's Sooty Boubou should be. In Kahuzi-biega National Park, this elevation corresponds with the park's eastern border, below 2000m are cultivated fields and tea plantations. The protected status and borders for the Itombwe region have not been established, but one thing that was clear from this trip is that any forest below the top of the plateau on the eastern side is under intense logging pressure. On the long hike up to our camp, we saw a few intriguing fingers of forest in ravines that reach down to elevations that might still have a few Willard's Sooty Boubou, but due to insecurity in the region, we did not get the opportunity to survey them.
A remaining patch of forest at about 1900m on the eastern slope of the Itombwe plateau.
Josh and I stayed on an extra week after Tom, traveling to Uganda. The goals were 1) to meet with our colleague, Makerere University Zoology Professor Robert Kityo about our permit applications for future work in Uganda, and 2) to reach Buhoma, the low elevation sector of Bwindi National Park where Tom et al. originally collected the specimens that proved to be Willard's Sooty Boubou. Josh and rented a van and successfully reached Buhoma, where we were pleased to meet up with the Alfred Twinomojoni, the dean of the Bwindi region bird guides and one of the crew who had worked with Tom et al back in 1997. As a professional bird guide, Alfred was aware of the new species description and he told us he could lead us in the park to look for the bird. We started early in the morning up the road from Buhoma into the park. This entire region is all below 1800m, what we think is the ideal elevation for willardi. Having not worked in forest at these elevations previously, the dramatic differences in bird species compared to sites above 2000m was impressive. Alfred knew all the calls, but even though he continued to whistle and play a recording of a rapid four noted whistle, no boubous responded.
The trail climbed and crossed a saddle; it was getting towards noon and threatening to rain. We stopped and ate lunch under a fruiting tree with several Great Blue Turacos (Corythaeola cristata). Alfred kept saying the boubous were there, they just were not responding. Reluctantly, we decided to start back to Buhoma. A little way up the trail there had been ants crossing and we could hear Red-tailed Bristle-bills calling (Bleda syndactyla) around that area. We were looking for the Bristle-bills when Josh suddenly yelled "I see a black boubou." I found it with my binoculars too. Alfred cued up the recording of the four noted whistle on his iPod. The bird started calling back with the four noted call. Josh started recording the bird and it started to rain. The rain soon made us retreat to a shelter up the trail, but when it stopped, we went back down to find the bird again. It started calling again almost immediately and its mate did also. At one point, the first bird was doing a raspy note and the other bird was doing a "chuck" comprising a duet. Josh even got some photos, but neither one of us could fully convince ourselves the eye was gray, which is what first keyed Tom Gnoske into thinking there might be two species involved. There just was not enough light even though we got fairly good looks. We are convinced that this call is something we have not heard from Mountain Sooty Boubous that we have now recorded from higher elevations at three other montane sites in the Albertine Rift (Nyungwe, Kahuzi-Biega, and Itombwe). Alfred confirmed that he hears this same difference with respect to boubous at the higher elevations at Bwindi. The bird at Buhoma is Willard's Sooty Boubou. As another piece of evidence, the recording on Alfred's iPod comes from a set of CDs of African bird songs made by Claude Chappuis. The four-noted call is one of the cuts under what Chappuis calls Laniarius fuelleboorni (poensis) holomelas ( the taxonomy of these boubous has been confused for along time, but in the Chappuis taxonomy the name refers to all Albertine rift black shrikes not matter what elevation). The notes for the CDs credit this recording to the late Jennifer Horne, and the location is given as Bwindi. We suspect these will prove to be from the Buhoma area. So... a mystery has been solved. By clicking on the play icon above, you can hear Josh Engel's recording of Willard's Sooty Boubou made in the rain (and thunder) on 3 May 2012 above Buhoma in Bwindi NP, Uganda; elevation about 1600m.
Tom Gnoske, Charles Kahindo, and Ben Marks in Uganda, 1997.