Sequential vigilance is unpredictable in reproductive Black-necked Cranes

Abstract

Abstract Background Vigilance 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. Methods Observations 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. Results Not 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. Conclusion Our 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.

Keywords

• Black-necked Cranes
• Instantaneous randomness
• Sequential randomness