We originally thought this bird was a Tanzanian Red-billed Hornbill, but it is actually a Northern Red-billed Hornbill.
The former Red-billed Hornbill (Tockus erythrorhynchus) has undergone a five-way split as follows:
- Northern Red-billed Hornbill (Tockus erythrorhynchus)
- Damara Red-billed Hornbill (Tockus damarensis)
- Southern Red-billed Hornbill (Tockus rufirostris)
- Tanzanian Red-billed Hornbill (Tockus ruahae) - new taxon
- Western Red-billed Hornbill (Tockus kempi) - new taxon
The key difference between T. ruahae and the others is a combination of large black eye-patch, white
face and contrasting yellow iris. Close examination of this individual reveals a dark brown iris, narrow dark orbital
and gray streaking on the face. These are all features of Northern Red-billed Hornbill. Most field guides do
not treat these taxa at all and their true ranges are only now being worked out.
The map in Kemp & Delport (2002) shows Northern Red-billed Hornbill ranging well into northern Tanzania and
Tarangire is close to the zone of contact between T. erythrorhynchus and T. ruahae. However more
recent studies have found that Northern is the expected Red-billed Hornbill east of the Rift Valley while Tanzanian
occurs to the west and south. Useful reference photos of both species and some tentative range maps are online
here and here.
Reference
Kemp, A.C. and W. Delport. 2002. Comments on the status of subspecies in the red-billed hornbill (Tockus erythrorhynchus)
complex (Aves: Bucerotidae), with the description of a new taxon endemic to Tanzania. Annals of the Transvaal Museum
39: 1-8. [PDF]
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