Effects of group size, habitat and hunting risk on vigilance and foraging behaviour in the Lesser Rhea (Rhea pennata pennata)
Fernando R. Barri A B , Nicolás Roldán A , Joaquín L. Navarro A and Mónica B. Martella A
+ Author Affiliations
- Author Affiliations
A Centro de Zoología Aplicada, Universidad Nacional de Córdoba, C.C. 122, Córdoba 5000, Argentina.
B Corresponding author. Email: fbarri@efn.uncor.edu
Emu 112(1) 67-70 https://doi.org/10.1071/MU10090
Submitted: 16 December 2010 Accepted: 31 August 2011 Published: 10 February 2012
Abstract
Gregariousness is a known anti-predator strategy, but factors other than the size of groups, such as the levels of predation pressure or habitat, can affect vigilance and foraging behaviour in birds. We studied the effects of group size, habitat (shrubland steppe v. meadows), and risk of hunting by humans (protected core area v. edge area exposed to poaching) on vigilance and foraging behaviour of wild populations of the Lesser Rhea (Rhea pennata pennata), a near-threatened ratite, in north-western Patagonia, Argentina. On average, Lesser Rheas allocated 18% of their time to vigilance and 67% to foraging. Individuals tended to be more vigilant with declining group size, in areas with low visibility that hinders escape by running, and in areas exposed to hunting, than in open habitats with abundant food or sites with low risk of hunting. Although time spent foraging was also influenced by habitat type and hunting risk, there was no direct relationship between foraging time and group size. As in other species of ratite, Lesser Rheas seem to take advantage of flocking as an anti-predation strategy. Our data do not only confirm the influence of group size, but also of habitat structure and hunting risk, in determining the behaviour of this flightless bird in the wild.
Additional keywords: anti-predation strategy, gregariousness, Patagonian steppe, ratite, time allocation.
References
Barri, F. R., Martella, M. B., and Navarro, J. L. (2008). Effects of hunting, egg harvest and livestock grazing intensities on density and reproductive success of Lesser Rhea Rhea pennata pennata in Patagonia: implications for conservation. Oryx 42, 607–610.| Effects of hunting, egg harvest and livestock grazing intensities on density and reproductive success of Lesser Rhea Rhea pennata pennata in Patagonia: implications for conservation.Crossref | GoogleScholarGoogle Scholar |
Barri, F. R., Martella, M. B., and Navarro, J. L. (2009a). Reproductive success of wild Lesser Rheas (Rhea pennata pennata) in north-western Patagonia, Argentina. Journal üur Ornithologie 150, 127–132.
| Reproductive success of wild Lesser Rheas (Rhea pennata pennata) in north-western Patagonia, Argentina.Crossref | GoogleScholarGoogle Scholar |
Barri, F. R., Martella, M. B., and Navarro, J. L. (2009b). Nest-site habitat selection by Lesser Rheas (Rhea pennata pennata) in north-western Patagonia, Argentina. Journal für Ornithologie 150, 511–514.
| Nest-site habitat selection by Lesser Rheas (Rhea pennata pennata) in north-western Patagonia, Argentina.Crossref | GoogleScholarGoogle Scholar |
Beauchamp, G. (2008). What is the magnitude of the group-size effect on vigilance? Behavioral Ecology 19, 1361–1368.
| What is the magnitude of the group-size effect on vigilance?Crossref | GoogleScholarGoogle Scholar |
Beauchamp, G. (2009). How does food density influence vigilance in birds and mammals? Animal Behaviour 78, 223–231.
| How does food density influence vigilance in birds and mammals?Crossref | GoogleScholarGoogle Scholar |
Bellis, L. M., Navarro, J. L., Vignolo, P., and Martella, M. B. (2006). Habitat preferences of Lesser Rhea in Argentine Patagonia. Biodiversity and Conservation 69, 90–93.
Benhaiem, S., Delon, M., Lourtet, B., Cargnelutti, B., Aulagnier, S., Hewison, A. J., Morellet, N., and Verhey, H. (2008). Hunting increases vigilance levels in roe deer and modifies feeding site selection. Animal Behaviour 76, 611–618.
| Hunting increases vigilance levels in roe deer and modifies feeding site selection.Crossref | GoogleScholarGoogle Scholar |
Bertram, B. C. R. (1978). Living in groups: predators and prey. In ‘Behavioural Ecology: An Evolutionary Approach’. (Eds J. R. Krebs and N. B. Davies.) pp. 64–96. (Sinauer: Sunderland, MA.)
Bertram, B. C. (1980). Vigilance and group size in Ostriches. Animal Behaviour 28, 278–286.
| Vigilance and group size in Ostriches.Crossref | GoogleScholarGoogle Scholar |
BirdLife International (2011). Rhea pennata. In ‘IUCN Red List of Threatened Species. Version 2011.2’. (International Union for Conservation of Nature and Natural Resources: Gland, Switzerland.) Available at http://www.iucnredlist.org/apps/redlist/details/100006003/0 [Verified 5 December 2011].
Boland, C. R. (2003). An experimental test of predator detection rates using groups of free-living Emus. Ethology 109, 209–222.
| An experimental test of predator detection rates using groups of free-living Emus.Crossref | GoogleScholarGoogle Scholar |
Bonino, N., Bonvisutto, G., Pelliza Sbriller, A., and Somlo, R. (1986). Hábitos alimentarios de los herbívoros en la zona central de área ecológica Sierras y Mesetas occidentales de la Patagonia. Revista Argentina de Producción Animal 6, 275–287.
Carro, M. E., and Fernández, G. J. (2008). Seasonal variation in social organization and diurnal activity budget of the Greater Rhea (Rhea americana) in the Argentinean pampas. Emu 108, 167–173.
| Seasonal variation in social organization and diurnal activity budget of the Greater Rhea (Rhea americana) in the Argentinean pampas.Crossref | GoogleScholarGoogle Scholar |
Carro, M. E., and Fernández, G. J. (2009). Scanning pattern of Greater Rheas, Rhea americana: collective vigilance would increase the probability of detecting a predator. Journal of Ethology 27, 429–436.
| Scanning pattern of Greater Rheas, Rhea americana: collective vigilance would increase the probability of detecting a predator.Crossref | GoogleScholarGoogle Scholar |
Codenotti, T. L., and Álvarez, F. (2000). Habitat use by Greater Rheas in an agricultural area of southern Brazil. Revista de Etologia 2, 77–84.
Elgar, M. A. (1989). Predator vigilance and group size in mammals and birds: a critical review of the empirical evidence. Biological Reviews of the Cambridge Philosophical Society 64, 13–33.
| Predator vigilance and group size in mammals and birds: a critical review of the empirical evidence.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaL1M3kslKltQ%3D%3D&md5=4a8fe2ee1c8a0816d03f27555a7da74dCAS |
Folch, A. (1992). Family Rheidae (Rheas). In ‘Handbook of the Birds of the World. Vol. 1: Ostrich to Ducks’. (Eds J. Del Hoyo, A. Elliott and J. Sargatal.) pp. 83–84. (Lynx Edicions: Barcelona.)
Hamilton, W. D. (1971). Geometry for the selfish herd. Journal of Theoretical Biology 31, 295–311.
| Geometry for the selfish herd.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaE3M3ktFWmsA%3D%3D&md5=ef642eaf56d7daca0842665d184c8b59CAS |
Handford, P. T., and Mares, M. A. (1985). The mating systems of ratites and tinamous: an evolutionary perspective. Biological Journal of the Linnean Society of London 25, 77–104.
| The mating systems of ratites and tinamous: an evolutionary perspective.Crossref | GoogleScholarGoogle Scholar |
Lehner, P. N. (1996). ‘Handbook of Ethological Methods.’ (Cambridge University Press: Cambridge, UK.)
León, R., Bran, D., Collantes, M., Paruelo, J. M., and Soriano, A. (1998). Grandes unidades de vegetación de la Patagonia. Ecología Austral 8, 125–144.
Lombardi, C. (1994). Feeding and vigilance in wild Greater Rhea harems. Bird Behaviour 10, 29–35.
| Feeding and vigilance in wild Greater Rhea harems.Crossref | GoogleScholarGoogle Scholar |
Martella, M. B., and Navarro, J. L. (2006). Conservación y Manejo de Ñandúes (Rhea americana y Rhea pennata). In ‘Manejo de Fauna Silvestre en Argentina’. (Eds M. Bolkovic and E. Ramadori.) pp. 39–50. (Secretaria de Ambiente y Desarrollo Sustentable: Buenos Aires.)
Martella, M. B., Renison, D., and Navarro, J. L. (1995). Vigilance in the Greater Rhea: effects of vegetation height and group size. Journal of Field Ornithology 66, 215–220.
Milton, S., Dean, W. R., and Siegfried, W. R. (1994). Food selection by Ostrich in southern Africa. Journal of Wildlife Management 58, 234–248.
| Food selection by Ostrich in southern Africa.Crossref | GoogleScholarGoogle Scholar |
Novaro, A. J., Funes, M. C., and Walker, R. (2000). Ecological extinction of native prey of a carnivore assemblage in Argentine Patagonia. Biological Conservation 92, 25–33.
| Ecological extinction of native prey of a carnivore assemblage in Argentine Patagonia.Crossref | GoogleScholarGoogle Scholar |
Pulliam, H. R. (1973). On the advantages of flocking. Journal of Theoretical Biology 38, 419–422.
| On the advantages of flocking.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaE3s7jt1OjsA%3D%3D&md5=dd858fabb5e9004e1416cc90d367c2c7CAS |
Raikow, R. J. (1968). Maintenance behavior of the Common Rhea. Wilson Bulletin 80, 312–319.
Roberts, G. (1996). Why individual vigilance declines as group size increases. Animal Behaviour 51, 1077–1086.
| Why individual vigilance declines as group size increases.Crossref | GoogleScholarGoogle Scholar |