4.4 Increased individual vigilance with tourism
Our study confirmed former studies (Wang et al., 2009; Che et al., 2018) that adults took the responsibility of anti-predator scanning with significant higher alert time expenditure and duration. Wildlife decrease individual vigilance and benefit from foraging by gathering in big flocks (Pulliam, 1973; Kong et al., 2020), but interspecific conflicts also increase with group size (Pulliam, 1973; Caro, 2005), and juveniles are more vulnerable to conflicts. So, in winter, we could observe many family groups (2 adults with 1-2 juveniles) forage separately from other large groups (Liu et al., 2008), so as to keep >80% of time in foraging for young birds (Wang et al., 2009). Whereas adults in family groups have to spent ~6% more time than adults in large groups in vigilance instead of foraging (Wang et al., 2009). Interestingly, in order to conquer high predation risk faced by family groups, both individual vigilance sequence organization and inter-scan intervals of black-necked cranes are randomly distributed throughout the year (Li et al., 2017), making vigilance bouts more unpredictable than predators could not initiate successful attack. Compared with other wintering grounds of black-necked cranes in China, including those at Caohai wetlands in Guizhou province (vigilance: 12.59-16.52%; Li and Ma, 1992), Napahai wetlands in Yunnan (vigilance: 11.74-17.05%) and Lhasa in Tibet (vigilance: 17.8-21.0%; Che et al., 2018), black-necked cranes in Dashanbao spent most time allocation to vigilance (27.30-31.28%); even higher than former research conducted here in 2008 (vigilance: 15.6-21.4%; Kong et al., 2008) before visitation opens for public tourists. Black-necked cranes in our study area are facing equivalent disturbance to the birds in Daqiao wetland (vigilance: 27.9±16.5%; Kong et al., 2020) with a large human density of 135 residents per square kilometers, about 80km away from Dashanbao. Similarly, individual vigilance of cranes in our study (observer distance) and in Daqiao are significantly affected by human disturbance (Kong et al., 2020). We believe that the predominant landscape of vast marshes in Napahai and Caohai wetlands, which the help of avoidance of human access to crane habitats contributed the lower anti-predator scans. Wintering habitats utilized by cranes in Dashanbao and Daqiao are farmland (Kong et al., 2018). From a historical view, our study also demonstrated that the explosive expands of nature-based tourism cause new threats to the threatened black-necked cranes (Li et al., 2014). So, we argue that it is likely that there is strong interference from tourism caused coordinated vigilance in black-necked cranes in our study.