EPOW - Ecology Picture of the Week

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Hornbill Indicators of East Africa

Credit & Copyright:  Dr. Bruce G. Marcot
  

Explanation:  Here's a story of a striking bird with unclear relationships.   This is the Jackson's Hornbill, found in east Africa.  Some authors have used its affinity for, and presence within, arid scrub and woodland habitats in the Rift Valley as indicators of key areas for conservation (Muriuki et al. 1997).  Indeed, here in the arid acacia woodlands surrounding saline Lake Bagoria of southern Kenya, Jackson's Hornbills seem to thrive (Harper et al. 2003).   Note the striking difference between sexes.  You can hardly miss the huge bill characteristic of this family ... superficially resembling toucans and araçaris of the New World tropics.  Female Jackson's Hornbills sport gray bills whereas males have the colorful orange bills with paler yellow tips.                                          This pair of Jackson's Hornbills hung around our lakeside field camp for the ten days we camped at Lake Baringo in the Rift Valley of southern Kenya, east Africa. Now here's the relationship puzzle. A very similar species of east Africa is the Von der Decken's Hornbill: Male Von der Decken's Hornbill, using an active termite mound as a perch and lookout site, here in Sinya Wildlife Management Area of northern Tanzania, east Africa. This is the male ... looking a lot like the male Jackson's Hornbill!    Some authorities and bird field guides separate the two as distinct species, with the Jackson's Hornbill as Tockus jacksoni and the Von der Decken's Hornbill as Tockus deckeni, and even note that the two do not overlap in distribution.  Well and good. Other sources, however, suggest that Jackson's Hornbill is a subspecies (Tockus deckeni jacksoni), or a race (Turner and Pearson 2015), of Von der Decken's Hornbill.  Looking at their similar habitats -- arid woodlands of tropical east Africa -- and their abutting ("parapatric") range distributions, and their similarities in appearance, diet, and vocalizations, some such relationship seems like a plausibility.   Both "species" occur at the base of Mount Nyiru in southern Kenya, where it might be most interesting to collect DNA specimens to determine their genetic affinities.   Regardless, both forms can indeed serve as indicators of healthy arid woodland ecosystems, and long may they both thrive.    Von der Decken's Hornbill, northern Tanzania. Information:      Harper, D. M., R. B. Childress, M. M. Harper, R. R. Boar, P. Hickley, S. C. Mills, N. Otieno, T. Drane, E. Vareschi, O. Nasirwa, W. E. Mwatha, J. P. E. C. Darlington, and X. Escuté-Gasulla. 2003. Aquatic biodiversity and saline lakes: Lake Bogoria National Reserve, Kenya. Hydrobiologia 500:259-276.      Muriuki, J. N., H. M. De Klerk, Williams, P H, L. A. Bennun, T. M. Crowe, and E. Vanden Berge. 1997. Using patterns of distribution and diversity of Kenyan birds to select and prioritize areas for conservation. Biodiversity and Conservation 6:191-210.      Turner, D. A., and D. J. Pearson. 2015. Systematic and taxonomic issues concerning some East African bird species, notably those where treatment varies between authors. Scopus 34:1-23.