Wildlife tourism, particularly bird watching and nature photography, can significantly disturb foraging wildlife. Our study in the Yellow River Delta Nature Reserve revealed that such activities increase the vigilance of red-crowned cranes, a behavior analogous to responses observed in other species facing disturbances like agricultural activities or fishing. Previous research has documented how various human activities can alter bird behavior. For instance, red-crowned cranes in the Yancheng Nature Reserve exhibit heightened vigilance in human-influenced wetland habitats such as rice fields and fish ponds, in contrast to areas with no human presence. However, the impact of birdwatchers on sandhill crane vigilance has been found to be minimal in their American stopover sites. Studies on brown bears indicate that they perceive tourists as a potential risk, leading to adjustments in their vigilance or displacement. Therefore, wildlife tourism centered around crane populations in the Yellow River Delta requires careful management to balance viewing opportunities with the cranes’ need for undisturbed foraging.
Our findings indicate that the presence of wildlife tourists affects red-crowned crane vigilance differently depending on the wetland habitat. In taller P. australis mosaic habitats, crane vigilance increased with tourist presence, whereas in shorter S. salsa habitats, vigilance levels remained unchanged. Vigilance frequency was notably higher in the P. australis mixed habitat compared to the S. salsa habitat. This suggests that the dense P. australis vegetation acts as a visual obstruction, hindering the cranes’ ability to detect threats, rather than providing a protective cover. Similar observations have been made in studies of granivorous passerines and semipalmated sandpipers, where limited visibility impacts vigilance and predator detection. The study’s analysis of vigilance frequency data, but not time budget data, highlights this effect. This specific vigilance strategy might stem from the cranes perceiving wildlife tourists as a low-level threat, requiring minimal time allocation for vigilance, or potentially due to habituation to human presence. Limitations in sample size prevented differentiating responses to bird-watching versus photography activities, warranting further investigation.
Vigilance behavior is often proposed as a non-invasive method for monitoring wildlife during tourist activities, as it resembles predator avoidance. However, some research emphasizes the importance of contextual factors, noting that vigilance can also serve to monitor conspecifics for potential food competition. Consequently, future studies should also examine other behavioral responses like flight initiation distance and displacement from foraging sites. Flushing, a common occurrence at the YRD, could impose significant energetic costs and lead to lost foraging opportunities for cranes, potentially more so than vigilance alone. Linking observed vigilance levels to the cranes’ body condition or health index would further quantify the actual impact and inform conservation management.
The lower frequency of vigilance behaviors in shorter S. salsa habitats under human disturbance might be attributed to specific adjustments in the cranes’ posture. Some research suggests that vigilance can be maintained even with a lowered head, provided there is no visual obstruction, as birds can still detect threats, albeit with reduced efficiency. In shorter vegetation, cranes may maintain awareness of their surroundings during head-down foraging, negating the need for frequent head-up vigilance. In contrast, the denser P. australis vegetation necessitates increased head-up vigilance to gather sufficient information about potential threats.
Consistent with other studies, juvenile red-crowned cranes exhibited lower vigilance frequency and spent less time being vigilant than adults in both habitat types. This is likely due to their higher nutritional requirements and inexperience in handling prey. Alternatively, juveniles may be less adept at threat detection or benefit from the protection of their parents. The observation that cranes maintain close proximity within family groups during migration supports this idea. Furthermore, vigilance decreased as the distance to human disturbance increased in both habitats. A minimum disturbance distance of 300 meters triggered high vigilance, aligning with previous research. This adjustment reflects a response to the perceived degree and type of threat.
Conservation Implications
Evaluating the effects and sustainability of wildlife tourism hinges on understanding whether individual animals choose to flee or tolerate human presence. For many species, the motivations behind tolerating human proximity remain under-researched. Studies on brown bears demonstrate that tourist behavior can influence an individual bear’s decision to stay or flee, potentially leading to displacement if tourists are allowed unrestricted close access. Given the influence of wildlife tourists on red-crowned crane vigilance, it is crucial to carefully manage all crane viewing tourism practices at the YRD to develop guidelines for responsible viewing. Appropriately managed wildlife viewing areas, with controls on tourist numbers and scheduled viewing times, can offer direct benefits to wildlife, such as enhanced foraging opportunities. While the impact of varying tourist group sizes was not explored, these findings suggest that managing the number of tourists and their viewing times is essential, particularly at critical foraging sites. Informing tourists about the potential consequences of their activities can help minimize negative impacts on crane vigilance, as regulations are more readily followed when the reasoning is understood.
Our data suggests that a minimum distance of 300 meters between observers and red-crowned cranes can serve as an appropriate threshold for tourism activities like photography at the YRD, without significantly impacting crane vigilance. This aligns with a similar study by Li (2011). Beyond this distance, vigilance frequency and, to a lesser extent, time spent vigilant remained relatively stable in both habitats. Brown bear studies have noted a decrease in vigilance behavior at distances greater than 100 meters from viewing tourists. Therefore, red-crowned cranes may continue foraging when tourist viewing sites are situated more than 300 meters away, a threshold that should be applied to other crane viewing sites across their wintering range, regardless of habitat type.
This study also carries important conservation implications for the habitat of migratory red-crowned cranes. The rapid spread of S. salsa vegetation into P. australis areas in the Yellow River Delta and other estuarine sites poses a concern. S. salsa vegetation in coastal areas is a vital foraging habitat for red-crowned cranes, as the tidal mudflat crabs inhabiting this environment constitute their primary food source. While cranes also utilize the taller S. salsa – P. australis mosaic habitat, the heightened vigilance required in this environment can reduce overall foraging effort and potentially hinder energy accumulation. Furthermore, crab biomass is lower in the mosaic habitat compared to pure S. salsa stands, and this vegetation is susceptible to invasion by Spartina alterniflora. The succession of taller P. australis and S. alterniflora may not only affect crane vigilance but also diminish habitat usability due to dense vegetation limiting accessibility. We recommend increased attention to the rapid loss of S. salsa vegetation and suggest that future habitat restoration efforts prioritize the provision of non-obstructive and prey-rich S. salsa habitats for migratory red-crowned cranes.
