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1 January 2002 Notes on Owl Pellets Found in the Udzungwa Scarp Forest Reserve, Tanzania
William T. Stanley, David C. Moyer, Elia A. Mulungu, James Pokines, Jenelle A. Bittner
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NOTES ON OWL PELLETS FOUND IN THE UDZUNGWA SCARP FOREST RESERVE, TANZANIAWilliam T. StanleyDivision of Mammals, Field Museum of Natural History 1400 South Lake Shore Drive, Chicago, IL 60605, U.S.A. Stanley@fieldmuseum.orgDavid C. Moyer, Elia A. MulunguWildlife Conservation Society, P.O. Box 936, Iringa, Tanzania. wcs@wcs.or.tzJames Pokines & Jenelle A. BittnerDivision of Mammals, Field Museum of Natural History 1400 South Lake Shore Drive, Chicago, IL 60605, U.S.A. James.Pokines@CILHI.Army.MilDuring a survey of the avifauna of the Udzungwa Scarp Forest Reserve in the Udzungwa Mountains, Tanzania, E. A. Mulungu found pellets on the forest floor that had been regurgitated by owls. Based on the size and consistency of the pellets we conclude that they were produced by the Usambara Eagle Owl Bubo poensis vosseleri and report the contents to contribute to the information regarding owls in Udzungwa forests. The pellets were found at 0800 hrs on 27 December 1997 at the following locality: Iringa Region, Iringa District, Udzungwa Scarp Forest Reserve, 10 km SE Mbawi (Massissiwe B), approximately 1,800 m and approximately 8°19'S and 35°55'E. The habitat was submontane forest and was relatively far from recently disturbed habitat (see Fjeldså, 1999). The specific habitat was in an ecotone between forest and tussock grass with a small stream running though the grass. One pellet was found on top of a clump of grass at the base of a dry dead tree leading Mulungu to conclude the pellets had been regurgitated by an owl (or owls) roosting in the tree. The other pellets were recovered after digging through the grass. All were recovered within a 1 m⟨sup⟩2⟨/sup⟩ area.A total of eight pellets were found ranging in size from 35 by 25 by 20 mm to 50 by 35 by 25 (table 1). Based on the size and consistency of the pellets, and the reasons presented below, we assume that they were produced by the Usambara Eagle Owl Bubo poensis vosseler). We have recorded vocalisations of the Eagle Owl less than 10 km from the site where the pellets were found (Moyer and Mulungu, in prep). T. Butynski and C. Ehardt have also recorded this eagle owl in the northern part of the Udzungwa Scarp Forest Reserve (pers. comm.). The only other candidate for a large owl (though not as big as the Eagle Owl) in the deep forest is the African Wood Owl Strix woodfordii which produces a friable pellet usually containing fine invertebrate remains (Fry et al., 1988). The pellets we collected were not friable and contained no invertebrate remains. The Barn owl Tyto capenis and the African grass owl T. alba produce pellets of roughly the size of the ones of this study, but we don't think either of these species produced the material we found based on the following:1.T. capensis has not been recorded in Udzungwa Mountain forest habitat, although T. Butynski and A. Perkin (pers. comm.) observed and recorded T. capensis in a large area of short grassland ("Luala Valley") within the Ndundulu Forest Reserve of the Udzungwas;2.Nests of T. capensis commonly include associated tunnels that pellets are found in or near and no such tunnels were found;3.T. alba is commonly found near human habitation and rarely in undisturbed forest habitats (Fry et al., 1988).Table 1. Aspects of mammal skulls found in eight owl pellets in the Udzungwa Scarp Forest, Tanzania. R = right, L = left. Adult and subadult determinations based on toothwear. Taxonomy follows Hutterer (1993) and Musser and Carleton (1993).PelletMeasurements (mm)Species found with parts of skull found145×25×202 Grammomys ibeanus: adult-rostral section of 1 cranium; 1 R, 1 L dentary; subadult-rostral section of 1 cranium; 1 R dentaryCrocidura hildegardeae: 1 L dentary235×25×202 Grammomys ibeanus: adult-rostral section of 1 cranium; 1 R, 1 L dentary; adult-1 L dentary1 Dendromys cf. nyikae: adult-1 R, 1 L dentary345×35×201 Grammomys ibeanus: adult-1 almost complete cranium; 1 R, 1 L dentary1 Myosorex kihaulei: rostral section of cranium, 1 L, 1 R dentary440×35×201 Grammomys ibeanus: adult-rostral section of 1 cranium; 1 R, 1 L dentary;1 Dendromys mysticalis: adult-1 partial cranium, 1 R, 1 L dentary545×30×201 Grammomys ibeanus: adult-1 complete cranium; 1 R, 1 L dentary1 Hylomyscus denniae: adult-rostral section of 1 cranium; 1 R, 1 L dentary650×35×252 Grammomys ibeanus: subadult-rostral section of 1 cranium; 1 R, 1 L dentary; subadult-rostral section of 1 cranium; 1 R, 1 L dentary2 Sylvisorex megalura: adult-rostral section of 1 cranium; 1 R, 1 L dentary; adult-rostral section of 1 cranium; 1 R, 1 L dentary7 (pellet made up of two parts)50×35×201 Grammomys ibeanus: adult-rostral section of 1 cranium; 1 R, 1 L dentary;30×25×201 Otomys cf. anchietae: adult-1 nearly complete cranium; 1 R, 1 L dentary858×25×301 Grammomys ibeanus: adult-complete rostral section of 1 cranium; 1 R, 1 L dentary1 Myosorex kihaulei: complete rostral section of cranium, 1 L, 1 R dentaryThe pellets were dissected to examine the prey remains, which were predominately mammalian. Each pellet contained the remnants of at least one mammalian cranium, as well as other bones. A list of the mammals found is presented in table 1. Although other skeletal elements of the species identified were found in the pellets, in each case none of the non-cranial elements contradicted the minimum number of individuals (MNI) estimated to be in each pellet based on cranial elements. Paired elements of the skull (dentaries, maxilla, etc.) were used to estimated the MNI listed in table 2.Table 2. Species composition of the eight owl pellets found. Mass measurements based on specimens collected from Udzungwa Scarp Forest Reserve and housed at the Field Museum of Natural History.SpeciesMNI% total individualsaverage mass in grams (n)% total biomassCrocidura hildegardeae15.36.7 (39)1.1Myosorex kihaulei210.510.1 (16)3.3Sylvisorex megalura210.56.1 (4)2.0Otomys cf. anchietae15.3115.7 (3)18.9Dendromus mystacalis15.35 (1)0.8Dendromus nyikae15.36.8 (1)1.1Grammomys ibeanus1052.642.9 (6)70Hylomyscus denniae15.317.5(27)2.8Totals19100613/19 = 32.3100All species identified in the remains are known from the Udzungwa Scarp Forest Reserve based on recent surveys (Stanley et al., 1998). All the species of rodents identified are scansorial in nature, with the exception of Otomys. Vernon (1972) reported on the remains of pellets produced by Tyto that contained remains of rodent species known to be primarily terrestrial, further evidence that the pellets reported here were not produced by Tyto. It is interesting to note that no ground dwelling rodents such as Praomys delectorum and Lophuromys flavopunctatus were found in the remains although these are the most abundant of any of the species of rodent we have observed during our surveys (Stanley et al., 1998). The shrews found in the remains are all strictly ground dwelling.ACKNOWLEDGEMENTSThis work was supported in part by the National Geographic Society (grant #5244-94), the Wildlife Conservation Society, the Danish Natural Science Research Council, and the Ellen Thorne Smith fund at Field Museum. We thank the Tanzanian Commission for Science and Technology and the Tanzanian Ministry of Natural Resources and Tourism for help with this project. Comments from Tom Butynski and an anonymous reviewer improved the manuscript.REFERENCESFjeldså, J. (1999). The impact of human forest disturbance on the endemic avifauna of the Udzungwa Mountains, Tanzania. Bird Conservation International 9: 47-62.Fry, C. H., S. Keith, & E. K. Urban (eds) 1988. The Birds of Africa. Vol. 3. Academic Press.Hutterer, R. (1993). Insectivora. In D. E. Wilson & D. M. Reeder (eds.), Mammal species of the world: a taxonomic and geographic reference. Smithsonian Institution Press, Washington, D.C. Pp. 69-130Musser, G. G. & M. D. Carleton (1993). Rodentia (Muridae). In D. E. Wilson & D. M. Reeder (eds.). Mammal species of the world: a taxonomic and geographic reference. Smithsonian Institution Press, Washington, D.C. Pp. 501-755Stanley, W. T., P. M. Kihaule, R. Hutterer, & K. M. Howell (1998). Small mammals of the Eastern Arc Mountains, Tanzania. Journal of East African Natural History 87: 91-100.Vernon, C. J. (1972). An analysis of owl pellets collected in southern Africa. Ostrich 43: 109-124.

William T. Stanley, David C. Moyer, Elia A. Mulungu, James Pokines, and Jenelle A. Bittner "Notes on Owl Pellets Found in the Udzungwa Scarp Forest Reserve, Tanzania," Journal of East African Natural History 91(1), 91-94, (1 January 2002). https://doi.org/10.2982/0012-8317(2002)91[91:NOOPFI]2.0.CO;2
Published: 1 January 2002
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