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Historical Biology: An International Journal of Paleobiology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ghbi20 The ecology and conservation of Asian hornbills: farmers of the forest Darren Naisha a Ocean and Earth Science, National Oceanography Centre, Southampton, University of Southampton, Southampton SO14 3ZH, UK Published online: 09 Sep 2014.

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To cite this article: Darren Naish (2015) The ecology and conservation of Asian hornbills: farmers of the forest, Historical Biology: An International Journal of Paleobiology, 27:7, 954-956, DOI: 10.1080/08912963.2014.919757 To link to this article: http://dx.doi.org/10.1080/08912963.2014.919757

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BOOK REVIEW

The ecology and conservation of Asian hornbills: that presents, analyses and discusses a huge amount of new farmers of the forest, by Margaret F. Kinnaird and data (Kinnaird and O’Brien 2007). It is thus more like a Timothy G. O’Brien, University of Chicago Press, 2007, monograph on the diversity, distribution, evolution, 315 pp., ISBN 978-0-226-43712-5 behaviour and conservation biology of Asian hornbills. Numerous subtitled sections, sidebars of text, graphs and Hornbills are among the most charismatic, fascinating and tables of data feature throughout. The volume is very much awesome of birds, yet surprisingly little is known of them, required reading for anyone seriously interested in the dedicated studies are few, and they are incredibly elusive biology, evolution, ecology and conservation of hornbills, and hard to study. Approximately 60 hornbill species but it is comprehensive enough and well-illustrated occur across tropical Africa and Asia, and also in the enough to be of broader appeal as well. A colour plate Middle East and Australasia. These are birds of super- section features a selection of beautiful, spectacular photos latives. The largest species have wingspans of over 1.5 m by Tim Laman. Small drawings by Jonathan Kingdon also and weigh as much as 6 kg (in the case of the Southern feature throughout the book. ground hornbill Bucorvus leadbeateri); some (the Great There are several great questions about hornbills, and I hornbill Buceros bicornis and Southern ground hornbill) hoped that some or all might be discussed or even can reportedly live for more than 60 or even 70 years. answered here. How is the hornbill casque used? Does Sexual dimorphism is extreme in some species, with the hornbill behaviour or ecology give us an insight as to males of some being as much as 66% larger than the which pressures contributed to casque evolution? How is females. Hornbills are slow to mature, Buceros not the casque formed in anatomical terms? What role do breeding until 4 or 5 years of age. hornbills play in the distribution of plant seeds and are they Hornbills are also birds of splendid and remarkable ‘keystone’ frugivores? How dependent are they on pristine anatomy. Great casques that form huge cylinders or areas of forest, and can they maintain viable populations in curved, rhino-like horns decorate the heads of some secondary or disrupted forest? How and why did their species. Furrows, grooves and serrations sometimes mark remarkable breeding strategy evolve? Do they find fruit (a their great, curved bills; giant, lavish eyelashes, enormous notoriously ephemeral and sometimes unpredictable tail feathers and brightly coloured neck and facial skin are resource in the tropics) thanks to a well-developed present in some species; and fused cervical vertebrae and memory, or are they merely opportunistic? How has their bilobular kidneys are peculiar to the group. The chicks of evolution and distribution been shaped by that of other some hornbills possess paired air sacs located on either fruit-eating groups, like primates? And so on. We are not side of the dorsal midline, the function of which (if they in the position to answer or even test many of these have one) is completely unknown. questions adequately for the simple reason that the data They are also birds of incredible habits. In most, the have not been collected [though note that some have been female becomes walled up – self-incarcerated – within studied since Kinnaird and O’Brien (2007) was published;

Downloaded by [American Museum of Natural History] at 02:31 30 August 2015 the nest chamber; the Helmeted hornbill Rhinoplax vigil see Viseshakul et al. 2011; Gonzalez, Sheldon and Tobias engages in aerial jousting contents; some species ‘paint’ 2013]. Nevertheless, Kinnaird and O’Brien provide their feathers and rhamphotheca with the oily secretions of copious data relevant to these issues and discuss them their under-tail glands; and cooperative breeding is the within context. norm in some groups of species (like the Anorrhinus Because the hornbill casque only develops at sexual brown hornbills). As large, slow-breeding animals that maturity and often exhibits sexual dimorphism (it is typically rely on large tracts of forest and reliable access to usually larger in males than in females), it seems plausible fruits and cavities in trees, hornbills are seriously that it functions as an indicator of maturity and evolved endangered by habitat loss and degradation, and within the context of sexual selection pressure (as is potentially by climate change and selective hunting. probably the case for other cranial casques and crests in Margaret Kinnaird and Timothy O’Brien’s 2007 The other archosaurs: Hone et al. 2012; Hone and Naish 2013). Ecology and Conservation of Asian Hornbills is not a The concept that the casques are ‘species identification popular retelling of other people’s research on these badges’ lacks compelling support and might be contra- fascinating birds, but a major piece of primary literature dicted by hybridisation events recorded between anato- Historical Biology 955

mically distinct species (Chamutpong et al. 2013). Adding geological past, and that forests, woodlands and savannahs support to a sexually selected role is the fact that the waxed and waned across this region in step with climatic casques of some hornbill species seemingly function as cycles. Hornbills must have employed overwater dispersal acoustic resonating chambers used to broadcast their at times: even during those parts of the Pleistocene when territorial vocalisations (Alexander et al. 1994) and that sea levels were about 180 m lower than present, the those of others are heavily reinforced internally and used Philippines, for example, were separated from Borneo by in aerial head-butting contents (Kinnaird et al. 2003). long stretches of water, and yet members of the group However, suggestions have also been made that the heavy ended up here in the form of several tarictic hornbills, and casques of some hornbills (the Helmeted hornbill in certain Buceros, Anthracoceros and Aceros species. particular) help the bill work as a hammer. From a historical perspective, the most interesting case The degree and distribution of sexual dimorphism in of all concerns Rhyticeros, since these occur on New hornbills is unusual: some species are monomorphic, Guinea and some of the surrounding islands, but are others have males that are slightly larger than females, and otherwise birds of peninsular south-east Asia, Borneo, others have males that are more than twice as large as Sumatra and Java. The Rhyticeros species are ‘known as females (Kinnaird and O’Brien 2007). Quite why this the great hornbill dispersers [being able to] fly 10–15 km range of dimorphism occurs, and why it is distributed in in a day’ (Kinnaird and O’Brien 2007, p. 30), and their the way that it is, remains mysterious, as there are few absence from Sulawesi, Flores, Timor and even Australia consistencies within particular hornbill lineages, or within is puzzling, as the birds either passed across these areas in species that share given regions or islands. More studies getting to where they are today, or are close enough for that link ecology and behaviour with phylogeny and them to be within easy flying distance. We might hope distribution are much needed. for fossils, archaeological specimens or even ethnic tales While mostly based on the conservation biology, that demonstrate or hint at the presence of hornbills in current threats and future of hornbills, a substantial section these regions, but nothing like this has been reported yet of the book reviews the evolutionary history of these birds. (Meijer 2014). Based on the fossil record of their close relatives (hoopoes Hornbills are specialised frugivores, able both to ingest and wood-hoopoes and their fossil kin), hornbills must huge quantities of fruit in a short period of time and have originated in the Eocene. However, essentially (almost certainly) to successfully capture and metabolise nothing is known in the way of their fossil record until the the very low protein concentrations present in many of the Miocene, and even then remains are scant and not fruits they eat. Fruits are so crucial to hornbills that especially informative with respect to patterns and trends Kinnaird and O’Brien (2007) discuss fruit diversity and in the evolution of the group (Naish 2012). biology, and the importance to hornbills of the species Of the several different phylogenetic hypotheses that concerned, at length. In keeping with other studies on have been published, most agree that ground hornbills tropical ecology, figs are emphasised as a keystone (Bucorvus) are the sister group of most remaining resource, searched for and utilised by frugivores even hornbills and that early hornbill evolution occurred in when other fruits are available (it should be noted that figs Africa. Kinnaird and O’Brien (2007) favour the view that a contain over 750 species, over 500 of which occur within hypothetical ancestral hornbill – they call it a ‘proto- the Asian hornbill realm). Chapter 4 – ‘Feeding ecology; Buceros’ and imagine it as a large, territorial, carnivorous how to survive on fruits’ – includes a huge amount of data hornbill – descended from Bucorvus-like ancestors and and discussion as goes the figs and the other fruits utilised gave rise both to (assumed) endemic African taxa such as by hornbills. Tockus and Tropicranus and to a more forest-adapted, Despite their efficiency as processors and digesters of Downloaded by [American Museum of Natural History] at 02:31 30 August 2015 frugivorous lineage that moved into Asia. Here, the group fruit, hornbills still need to consume 60–600 g of them per radiated extensively, later reinvading Africa to give rise to day, quantities equivalent to 20–33% of their body weight Ceratogymna and Bycanistes. This model is more or less (Kinnaird and O’Brien 2007). Presumably as a conse- consistent with the topologies recovered in recent quence of their fruit-rich diet, they hardly ever drink and phylogenetic analyses (Gonzalez, Sheldon, Collar, et al. seem especially efficient at processing water. Kinnaird and 2013). O’Brien (2007) note that this may be linked to the unusual, Kinnaird and O’Brien (2007) provide an extensive bilobed form of hornbill kidneys. This efficient water discussion of hornbill phylogeny and biogeography in extraction almost certainly explains why their faeces are south-east Asia and northern Australasia, discussing the drier than tends to be the case for birds, and this is turn key features, distribution and biology of each hornbill might help explain how dung came to be co-opted as a genus in turn. Hornbill biogeography across the so-called nest-building material in the group. Asian hornbill realm is an area made highly complex by The last section of The Ecology and Conservation of the fact that different parts of the Sunda Shelf region were Asian Hornbills is devoted to the threats that face hornbills exposed and submerged at different points in the and their environments. Logging, the spread of plantations 956 Book Review

and loss of connected forest tracts, the ecology of fire, seed dispersal and ecology, and on conservation. As usual, human population expansion, poor management, govern- the price is problematic and means that it is out of reach to ment corruption, hunting, fuelwood collection, local interested amateurs and those without grants or insti- poverty, the development of infrastructure and yet other tutional support. In summary, it is a highly impressive and factors paint a highly complex picture of interaction, the important tour-de-force that provides a wealth of links between these factors being confusing, sometimes information on the past, present and future of Asian counter-intuitive, complicated and under-researched. It is a hornbill biology. deeply topical subject given the current pace of habitat change in the Asian hornbill realm and the near- unstoppable, unregulated monster that is the palm oil References industry. Alexander GD, Houston DC, Campbell M. 1994. A possible acoustic Exactly what this grand, evolving mess means for the function for the casque structure in hornbills (Bucerotidae). J Zool. 233:57–67. distribution and health of hornbill populations, and for Chamutpong S, Ponglikitmongkol M, Charoennitikul W, Mudsri S, sympatric plants and animals, is neither simple nor clear. Poonswad P. 2013. Hybridisation in the wild between the Great Urbanisation, for example, means that people may have hornbill (Buceros bicornis) and the Rhinoceros hornbill (Buceros less impact on forests, and hence on hornbills, and also that rhinoceros) in Thailand and its genetic assessment. Raffles Bull Zool. 61:349–358. regulations and rules concerning land-use will increas- Datta A. 1998. Hornbill abundance in unlogged forest, selectively logged ingly come into play ... theoretically, that is. Indeed, as forest, and a forest plantation in Arunachal Pradesh, India. Oryx. Kinnaird and O’Brien (2007) discuss, collusive corruption, 32:285–294. Gonzalez J-CT, Sheldon BC, Collar NJ, Tobias JA. 2013. A bribery and unregulated logging have been serious comprehensive molecular phylogeny for the hornbills (Aves: problems across the hornbill realm, especially in Bucerotidae). Mol Phylogenet Evol. 67:468–483. Indonesia, the Solomon Islands and Papua New Guinea. Gonzalez J-CT, Sheldon BC, Tobias JA. 2013. Environmental stability and the evolution of cooperative breeding in hornbills. Proc R Soc B. Anyway, as goes the future, hornbill species are under 280:20131297. threat as forest blocks are broken up, degraded and made Hone DWE, Naish D. 2013. The ‘species recognition hypothesis’ does ever more accessible to hunters, loggers and others who not explain the presence and evolution of exaggerated structures in non-avialan dinosaurs. J Zool. 290:172–180. exploit hornbill habitats. Birds like hornbills may persist Hone DWE, Naish D, Cuthill IC. 2012. Does mutual sexual selection across such fragmented landscapes, but at lower explain the evolution of head crests in pterosaurs and dinosaurs? population densities. However, some studies indicate Lethaia. 45:139–156. Kinnaird MF, Hadiprakarsa Y-Y, Thiensongrusamee P. 2003. Aerial that big, frugivorous birds and other animals are relatively jousting by Helmeted hornbills Rhinoplax vigil: observations from resilient to the activities of the logging industry or, Indonesia and Thailand. Ibis. 145:506–508. counter-intuitively, may even benefit from them (Plumptre Kinnaird MF, O’Brien TG. 2007. The ecology and conservation of Asian hornbills: farmers of the forest. Chicago, IL: University of Chicago and Greiser-Johns 2001). Caveats that need to be kept in Press. mind are that the term ‘frugivore’ is slightly ambiguous Meijer HJ. 2014. The avian fossil record in Insular Southeast Asia and its and not used consistently across all studies, and that it may implications for avian biogeography and palaeoecology. Peer J. 2: be dangerous or misleading to assume that what goes for e295. http://dx.doi.org/10.7717/peerj.295 Naish D. 2012. Birds. In: Brett-Surman MK, Holtz TR, Farlow JO, one hornbill species may go for another (Datta (1998) editors. The complete dinosaur. 2nd ed. Bloomington and found that Great hornbills, Oriental pied hornbills Indianapolis, IN: Indiana University Press; p. 379–423. Anthracoceros albirostris and Wreathed hornbills Rhyti- Plumptre A, Greiser-Johns A. 2001. Changes in primate communities following logging disturbance. In: Fimbel RA, Grajal A, Robinson ceros undulatus differed in how they responded to logging JG, editors. The cutting edge: conserving wildlife in logged tropical disturbance). Kinnaird and O’Brien (2007)discuss forests. New York, NY: Columbia University Press; p. 71–92. simulations and projections that pertain to forest Viseshakul N, Charoennitikul W, Kitamura S, Kemp AC, Thong-aree S,

Downloaded by [American Museum of Natural History] at 02:31 30 August 2015 Surapunpitak Y, Poonswad P, Ponglikitmongkol M. 2011. A fragmentation and what it means for hornbills – there is phylogeny of frugivorous hornbills linked to the evolution of Indian a huge quantity of data and discussion here. plants within Asian rainforests. J Evol Biol. 24:1533–1545. The Ecology and Conservation of Asian Hornbills: Farmers of the Forest is excellent and data-packed and will Darren Naish be used regularly by those interested academically in Ocean and Earth Science, National Oceanography Centre, hornbills, in the ecology or biology of tropical forest birds, Southampton, University of Southampton, or in avian conservation in the tropics. It is definitely not a Southampton SO14 3ZH, UK general guide to hornbills or to Asian hornbills as a whole, [email protected] however, and should be considered primarily focused on q 2014, Darren Naish