Initial Trends of Bird Assemblages Before and After River Diversion in an Endemic-rich African Forest

Abstract

The Lower Kihansi Hydropower Project in southern Tanzania caused the diversion of the Kihansi River from the Kihansi Gorge in the year 2000. By sampling the understorey avifauna prior to diversion, we examined (i) whether the adjacent Udagaje Gorge was an adequate control for observations in the Kihansi Gorge; (ii) which species of conservation interest occurred; and, (iii) which season best suited annual monitoring. Species composition and capture rates at three and two elevational transects in the Kihansi Gorge and Udagaje Gorge, respectively, confirmed that Udagaje had a comparable avifaunal assemblage to Kihansi. The cold season was most appropriate for population monitoring because >2 times more individuals were captured in the cold than hot season at both gorges, and at least four altitudinal migrants were present in the cold but not hot season. Post-diversion sampling revealed that only the Upper Kihansi transect suffered a significant decrease in number of individuals, a result that was driven largely by a decline in the Little Greenbul, Andropadus virens. This transect is closest to the Kihansi waterfall and associated spray zone which were lost after river diversion. Lack of differences in bird communities at other transects after diversion illustrates that early post-diversion effects on birds are probably concentrated near the base of the main falls. Together with studies of other biota in Kihansi, we propose that longterm monitoring is necessary to understand the factors that regulate changes in species composition of this threatened forest site.

Altitudinal migration by birds: a review of the literature and a comprehensive list of species

“…, Cordeiro et al. ). Here, we use the term altitudinal migration for the seasonal altitudinal movement of individuals from breeding areas to non‐breeding or wintering areas, including both short‐ or long‐distance movements.…”

Effect of an impoundment on nutrient dynamics in the Kihansi River, Tanzania

“…Obvious impacts on endemic species downstream at the Kihansi Gorge have since been observed. Many studies have been carried out on the impact of reduced water flow in the Kihansi Gorge, focusing on flora (Lovett et al 1997, Quinn et al 2005 and fauna, such as the Kihansi spray toad Nectophrynoides asperginis (Poynton et al 1998, Krajick 2006, and bird assemblages (Cordeiro et al 2006). Nitrogen and phosphorus in the Kihansi River have not been studied, despite their importance to downstream aquatic communities.…”

Back to Africa: monitoring post‐hydropower restoration to facilitate reintroduction of an extinct‐in‐the‐wild amphibian

“…However, there are no rivers on the escarpment of comparable volume to the Kihansi River and no known areas where a large volume of spray maintains a habitat comparable to the Kihansi Gorge wetlands. Further, the Kihansi River Gorge was home to other endemic and severely range-restricted plants , Vollesen 2000, Cheek 2003, Burgess et al 2004, Davis and Mvungi 2004, Rija et al 2011) and animals (Poynton et al 1998, Zilihona et al 1998, Dinesen et al 2001, Menegon et al 2004, Cordeiro et al 2006, Menegon 2008) that have, unfortunately, received much less attention than the Kihansi spray toad. The fate of these species after the diversion and the effectiveness of the irrigation system in mitigating negative impacts remain uncertain (see Davis and Mvungi 2004) and merit further study.…”

“…However, although the geographic extent of the project is relatively small, it is located in a biodiversity hotspot where almost any development potentially has a substantial negative impact on biodiversity (Myers 1988, Fjeldså and Lovett 1997, Myers et al 2000, Brooks et al 2002, Burgess et al 2004. The Udzungwa Mountains are exceptionally rich in species of restricted range size (Lovett andWasser 1993, Burgess et al 1998) and the forests in the Kihansi and Udagaji Gorges contain many Eastern Arc endemics and globally threatened plants , Vollesen 2000, Cheek 2003, Burgess et al 2004, Davis and Mvungi 2004, Rija et al 2011) and animals (Poynton et al 1998, Zilihona et al 1998, Dinesen et al 2001, Menegon et al 2004, Cordeiro et al 2006, Menegon 2008, including the ovoviviparous Kihansi spray toad Nectophrynoides asperginis (Poynton et al 1998, Taplin et al 1999, Channing et al 2006. At the time of its discovery in 1996 the Kihansi spray toad occurred in a spray wetland habitat of about 4 ha maintained by spray from falls on the Kihansi River.…”