Abstract
BackgroundVigilance refers to the behavior of animals scanning their surroundings with a main purpose of anti-predation. Whether vigilance can serve the function of anti-predation depends on its unpredictability, meaning instantaneous randomness, sequential randomness, and independence, the three assumptions from Pulliam model (J Theor Biol 38:419, 1973). Here we tested two of these three assumptions in reproductive Black-necked Cranes (Grus nigricollis) in Tibetan Plateau: instantaneous randomness and sequential randomness.MethodsObservations were carried out in July and September of 2014, July and August in 2017 in Selincuo National Nature Reserve, Tibet, with the help of focal sampling method. For instantaneous randomness, we used Kolmogorov–Smirnov test for its negative exponential distribution; for sequential randomness, we used Run test, correlation analysis, and generalized linear model to see if an inter-scan and its previous scan were correlated.ResultsNot similar to some recent studies, we did not find a significant predictable vigilance in this crane. Most inter-scan intervals (86/100, 86.0%) passed negative exponential distribution test, meaning vigilance sequences with instantaneous randomness; most inter-scan intervals (91/100, 91.0%) passed sequential random test, showing vigilance sequences were random organized.ConclusionOur results suggest that keeping a vigilance pattern with unpredictability is beneficial to the survival of the Black-necked Cranes, which are facing with both cruel natural environments and high predation risks.
Highlights
Vigilance refers to the behavior of animals scanning their surroundings with a main purpose of antipredation
Instantaneous randomness and sequential randomness both derive from the assumption that scanning is controlled by a single parameter: the rate of scan initiation (Pulliam 1973; Bednekoff and Lima 1998)
We considered the inter-scan intervals were randomly organized if they passed the negative exponential distribution test, and we calculated its parameter λ, which was the only determinant of the distribution
Summary
Vigilance refers to the behavior of animals scanning their surroundings with a main purpose of antipredation. Whether vigilance can serve the function of anti-predation depends on its unpredictability, meaning instantaneous randomness, sequential randomness, and independence, the three assumptions from Pulliam model (J Theor Biol 38:419, 1973). If the vigilance has a certain pattern or regularity, or called predictability, it will be known and grasped by a potential predator. The Pulliam’s vigilance model (Pulliam 1973) was proposed based on three assumptions: instantaneous randomness in scan initiation, sequential randomness in the duration of successive inter-scans, and independent scanning by different group members. An individual scanning in such a manner would produce inter-scan intervals following a negative exponential distribution. Such a distribution has no central tendency or ‘hump’ but, instead, shows a smoothly decreasing slope as longer intervals become geometrically less likely
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