4.2 Collective vigilance and affecting factors
Our study indicated that cooperative vigilance shift was disturbance and
predation risk dependent. Many studies demonstrated that cooperative
sentinel activity (one form of coordinated vigilance) increase when pups
are present (Santema and Clutton-Brock, 2013) and when predation risk
becomes greater (Ridley et al., 2010; Rauber and Manser, 2017). These
findings support our findings that cranes coordinate vigilance pattern
when more young birds are present, in high disturbance areas and when
humans show proximity. In our study, we considered the number of
juveniles in a family as predation vulnerability or risk (Xu et al.,
2013), as predators prefer hunting those left behind (Sirot and
Touzalin, 2009), more juveniles cost more individuals and collective
alert time of adults (Table 1). Leading parents to adopt time-consuming
coordinated vigilance strategy (Figure 2) as our study indicated.
Significant interactive effects of family type and observer distance on
adult collective vigilance indicate that cranes with juveniles are more
vulnerable to human disturbance. Our study also emphasizes that
coordinated vigilance or sentinel behaviour may actually exist in
relatively vast systems in small family groups (Ward, 1985; Wickler,
1985), under circumstances with significant disturbance and predation
risk (Rauber and Manser, 2017), even for monogamous breeding systems
(Mainwaring and Griffith, 2013) as in black-necked cranes.