Tyto alba: A Barn Owl from the Dinaledi Chamber, Maropeng Cradle of Humankind.

The Dinaledi Chamber in the Rising Star Cave forms part of the Maropeng Cradle of Humankind complex of caves in Gauteng State, to the northwest of Johannesburg, South Africa. Like many other caves in the system it was visited from time-to-time by cavers for several decades, but was not formally investigated by scientists until September 2013, when the skeletons of a previously unknown Hominin species were discovered there, and named Homo naledi. A number of Bird bones were discovered at the same time as the Hominin remains, but have not previously been formally identified or described.

In a paper published in the South African Journal of Science on 27 November 2018, Ashley Kruger and Shaw Badenhorst of the Evolutionary Studies Institute at the University of the Witwatersrand describe the Bird remains found inside the Dinaledi Chamber in 2013 as the remains of a Barn Owl, Tyto alba.

Barn Owls are one of the most widely distributed Birds on Earth, being found in almost all terrestrial environments, with the exception of Antarctica, the central Sahara, and some remote islands. They nest in enclosed spaces, including hollow trees, Human-built structures (such as barns) and caves, a habitat they are particularly known to favour in parts of South Africa where caves are often the best cover available in wide areas of open grassland.

The Dinaledi Chamber material comprises a largely complete tarsometatarsus, the mid-distal shaft and part of the distal condyle of a left tibiotarsus, the distal, mid and proximal shaft of a right radius, and proximal, mid and distal shaft, plus a small portion of the distal articulation of a right ulna. These were found on a raised platform within the Dinaledi Chamber, alongside some other bone material, though as the Owl bone fragments show no signs of re-mineralisation, they are assumed to be much younger than those of the Homo naledi specimens found within the cave, and their placement is therefore assumed to be due to the activities of modern cavers.

(a) Specimen U.W. 101 40C, a left tibiotarsus fragment of Tyto alba, with the mid-distal shaft present, and part of the distal condyle; (b) specimen U.W. 101 40B, a right radius fragment of Tyto alba, consisting of the distal, mid and proximal shaft, with the distal styloid process absent; (c) specimens U.W. 101 965 and 822, a right ulna fragment of Tyto alba, consisting of the proximal, mid and distal shaft, with a small portion of the distal articulation present. Kruger & Badenhorst (2018).

Kruger and Badenhorst suggest several ways in which the bones might have got into the Dinaledi Chamber. Firstly, they suggest the Owl might have flown into the cave system and got lost, eventually perishing in the chamber. Secondly, they suggest that the Owl might have fallen down a narrow shute close to the chamber, although this would not put the remains actually in the chamber (not a major problem, as the bones are presumed to have been moved onto the platform by Human activity). Thirdly, the bones might have been carried into the cave system from elsewhere by a modern caver, though why anybody should do this is unclear. Fourthly, it is possible that there was once a second entrance to the chamber, which has since been sealed, and that, therefore, both the Owl and the Hominins were actually entering a cave much closer to the surface, something which has been suggested by palaeontologist Francis Thackeray, though no evidence for such a second entrance has been found to date.

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The diet of breeding Grass Owls in Thailand.

Grass Owls are members of the Barn Owl family, Tytonidae, distinguished by their habit of roosting and nesting in tall grasses or other ground-cover plants, rather than trees. Until fairly recently all Grass Owls were thought to belong to a single species, but there are now two species recognised, the African Grass Owl, Tyto capensis, which is found across much of Africa, and the Eastern Grass Owl, Tyto longimembris, which is found in south China, Nepal, India, Myanmar, Southeast Asia, Indonesia, the Philippines, New Guinea, New Caledonia and Australia. The Eastern Grass Owl was first discovered in Thailand as recently as 2006, where a small colony was found nesting in a small area of marsh grassland called Nong Lom in Mae Jan District in Chiang Rai Province in the north of the country. 

In a paper published in the Raffles Bulletin of Zoology on 17 February 2015, Akalak Kunsorn of the Department of Biology at Chiang Mai University and the Environmental Ornithology Research Unit at Mahidol University, Siriwadee Chomdej of the Department of Biology and the Materials Science Research Center at Chiang Mai University, Narit Sitasuwan, Prasit Wangpakapattawong and Chatmongkon Suwannapoom, also of the Department of Biology at Chiang Mai University and Brett Sandercock of the Division of Biology at Kansas State University, describe the results of a study of the diet of the Grass Owls of Nom Long carried out by examining Owl pellets from the site during the breeding season.

Eastern Grass Owl, Tyto longimembris, in flight. Rob Hutchinson/The Owl Pages.

Birds lack teeth with which to process food like mammals, instead grinding it up in a muscular gizzard before it is passed to the stomach. As flying animals they are obliged to keep their weight to a minimum, and therefore need to dispose of inedible parts of their prey as quickly as possible, and so both Owls and Raptors regurgitate pellets comprising indigestible items such as fur and bone without passing them through the stomach and gut.

As well as Grass Owls the Nom Long site is also home to four species of Harriers; the Eastern Marsh Harrier, Circus spilonotus, the Pied Harrier, Circus melanoleucos, the Hen Harrier, Circus cyaneus and the Western Marsh Harrier, Circus aeruginosus. Grass Owl pellets tend to be larger and more elongate than Harrier pellets, but to avoid confusion Kunsorn et al. collected pellets only from the nests of Owls.

Kunsorn et al. carried out DNA tests on bones recovered from Owl pellets at Nom Long, in order to determine identify animals being consumed by the Owls. They were able to identify three species of Rodent by this method, the Black Rat, Rattus rattus, the Asian House Mouse, Mus musculus, and the Ricefield Mouse, Mus caroli. In addition wings and tails of Barn Swallows, Hirundo rustica, were also found in the Owl nests, suggesting that these Birds were also being consumed.

Pellets of the Eastern Grass Owl, Tyto longimembris, collected from nests at Nom Long. Kunsorn et al. (2015).

The diet of Eastern Grass Owls has previously been studied in southern Taiwan, where they were found to be consuming Lesser Rice-field Rats, Rattus losea, Ricefield Mice, Mus caroli, Formosan Blind Moles, Mogera insularis, House Shrews, Suncus murimus, Shrews Crocidura spp. and juvenile Formosan Hares, Lepus sinensis, as well as small Birds. This is a far larger range of prey than consumed at the Thai site, which Kunsorn et al. attribute to the more varied hunting grounds available to the Taiwan Owls. Nom Long is largely surrounded by grasslands and wetlands, with some Orange orchard about a kilometre away to the northwest, while the Taiwan site was within easy reach of shrubland, Rice paddies, Bamboo forest, Sugarcane fields, Mango orchards and Human settlements.

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Fossil Owls from the Early Pliocene of Langebaanweg, South Africa.

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Fossil Owls from the La Brea Tar Pits.

The La Brea Tar Pits are located in what is now central Los Angeles, California. They are essentially oil deposits identical to those worked by oil drills in other parts of the world, but exposed at the surface. When oil deposits are exposed in this way the lighter fractions (crude oil is made up of a mixture of different oils, known as 'fractions' due to the process used to separate...

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