Adaptation of migratory Tibetan antelope to infrastructure development

ABSTRACT Background: The Tibetan antelope (Pantholops hodgsonii) is a migratory ungulate species that inhabits the Qinghai–Tibet Plateau. In recent years, the population of Tibetan antelope has steadily increased owing to rigorous protection measures to safeguard the species from commercial poaching. Currently, infrastructure development, competition with domestic livestock, and predation are the principal factors threatening the survival of Tibetan antelope. Result: Our study found that migratory Tibetan antelope can adapt to the development of infrastructure over time, decreasing the potential negative impacts of such developments. Conclusion: We, therefore, urge infrastructure development companies to incorporate wildlife corridors that enable free movement of wildlife populations, particularly for migratory species.


Introduction
The development of infrastructure can lead to an increase in animal-traffic conflicts and synurbization of many ungulates (Forman and Alexander 1998;Apollonio, Andersen, and Putman 2010;Wyckoff et al. 2018). The Tibetan antelope (Pantholops hodgsonii) is a migratory ungulate that is also endemic to the Qinghai-Tibet Plateau (Schaller 1998). The species declined from over one million individuals in the mid-1980s to fewer than 70,000 a decade later owing to severe commercial poaching for their underfur. As a result of rigorous protection, the population has steadily increased from the year 2000 onwards (Schaller 2012). Consequently, the species' conservation status was changed from "Endangered" to "Near Threatened" in 2016 on the IUCN red list of threatened species (IUCN SSC Antelope Specialist Group 2016), showing considerable improvement.

Migratory populations of Tibetan antelope on the Qinghai-Tibet Plateau
Tibetan antelope exhibits sexual dimorphism ( Figure  1.1), which allows for individuals to be separated into same-sex groups (Figure 1.2) outside of the rutting season (Schaller et al. 2006). Only the female Tibetan antelope migrate. On the Qinghai-Tibet Plateau, at least four migratory populations of Tibetan antelope occur, as well as several sedentary populations (Schaller 1998). According to their distribution, the four migratory populations could be divided by region: the western Chang Tang, the middle Chang Tang, the eastern Chang Tang, and the Qinghai populations. During the migratory season, thousands of female Tibetan antelope congregate from early May to give birth (Figure 1.3) and then return to wintering grounds with their offspring in late August, about four months later (Schaller 1998;Buho et al. 2011). The return journey of female Tibetan antelope back to their wintering grounds after calving takes substantially longer owing to the slow pace of newborn calves (Manayeva et al. 2017).

Primary threats to the survival of Tibetan antelope on the Qinghai-Tibet Plateau
In the absence of poaching, the Tibetan antelope is primarily threatened by the expansion of human infrastructure ( Figure 2.1), resource competition with domestic livestock (Figure 2.2), and predation ( Figure  2.3) (Leslie and Schaller 2008). Infrastructure development that can encroach on this species' habitat includes the construction of roads, high-voltage power lines, oil pipelines, and other similar types of infrastructure. Besides habitat destruction and fragmentation ( Figure 2.1), roads can increase the likelihood of Tibetan antelope being killed in vehicle collisions and can also affect their behavioral responses, such as their vigilance levels, flight response, and overall movement patterns (Forman and Alexander 1998;Lian et al. 2012Lian et al. , 2011Xu et al. 2019).

Tibetan antelope adaptation to infrastructure development
Of the four migratory populations of Tibetan antelope, only the Qinghai population is threatened by the potential negative impacts of infrastructure development (Schaller et al. 2006;Manayeva et al. 2017). The Qinghai population of Tibetan antelope migrates between the Kekexili National Nature Reserve and the Sanjiangyuan National Nature Reserve. This population receives more conservation attention owing to the development of the Qinghai-Tibet Highway (QTH) and the Qinghai-Tibet Railway (QTR), which traverses their migratory routes. During their annual migration, migrating Tibetan antelope are required to cross both the QTH and the QTR twice. The impacts of roads on wildlife are more severe than other forms of infrastructure owing to the additional urban development and increased human disturbance that accompanies such developments. The QTR has 26 wildlife corridors that are included in its design. Subsequently, Tibetan antelope have adapted their migratory movements to include the use of these corridors (Yang and Xia 2008; Figure 3.1). Additionally, during hours of low volume road traffic, migratory antelope cross the QTH (Figure  3.1). Individual antelope have also been observed foraging or resting under the bridges of the QTR (Figure  3.2) and under high-voltage power lines (Figure 3.3), suggesting that they have become accustomed to the presence of the infrastructure. Similar behavioral responses have been observed in mule deer     Figure 3.1A shows that migrating Tibetan antelope are required to cross both the QTH and the QTR twice each year. Figure 3.1B shows the Wubei Bridge of the QTR, which was used by more than 90% of migratory antelope in our study.  (Odocoileus hemionus) in North America (Sawyer, Chad, and Thomas 2012).

Conclusion
Substantial infrastructural development on the Qinghai-Tibet Plateau has threatened the disruption of critical migratory routes for Tibetan antelope. This study included 18 years of population monitoring, which shows that Tibetan antelope have adjusted their behavior to cope with the presence of the QTR and QTH. Additionally, they have learned how to utilize wildlife corridors incorporated into the infrastructure during their migration. Construction of major infrastructure can have considerable negative impactson wildlife species; however, our study suggests that some of these impacts may decrease over time as species develop adaptive responses. Furthermore, environmental considerations such as the incorporation of wildlife corridors into infrastructure, are essential for allowing species to display normal movement behaviors, particularly for migratory species. Ensuring the sustainability of the free-flowing movement of wildlife populations is also vitally important for sustaining genetic diversity within populations.