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Biol Lett. Aug 23, 2010; 6(4): 475–477.
Published online Feb 3, 2010. doi:  10.1098/rsbl.2009.1016
PMCID: PMC2936201
The presence of an avian co-forager reduces vigilance in a cooperative mammal
Lynda L. Sharpe,1,2* Abigail S. Joustra,1 and Michael I. Cherry1
1Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
2Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0020, South Africa
*Author for correspondence (sharpelynda/at/
Received December 7, 2009; Accepted January 11, 2010.
Many animals must trade-off anti-predator vigilance with other behaviours. Some species facilitate predator detection by joining mixed-species foraging parties and ‘eavesdropping’ on the predator warnings given by other taxa. Such use of heterospecific warnings presumably reduces the likelihood of predation, but it is unclear whether it also provides wider benefits, by allowing individuals to reduce their own vigilance. We examine whether the presence of an avian co-forager, the fork-tailed drongo (Dicrurus adsimilis), affects rates of vigilance (including sentinel behaviour) in wild dwarf mongooses (Helogale parvula). We simulate the presence of drongos—using playbacks of their non-alarm vocalizations—to show that dwarf mongooses significantly reduce their rate of vigilance when foraging with this species. This is, to our knowledge, the first study to demonstrate experimentally that a mammal reduces vigilance in the presence of an avian co-forager.
Keywords: eavesdropping, heterospecific warnings, vigilance, sentinel behaviour, dwarf mongoose, fork-tailed drongo
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