Population viability analysis of Critically Endangered white-rumped vultures Gyps bengalensis

Abstract

More than a decade has passed since the catastrophic population decline in Gyps species was reported from South Asia, but much uncertainty remains about quantifying their short-term extinction risk. To estimate the future extinction risk of the white-rumped vulture Gyps bengalensis in Nepal, we conducted counts at 7 nesting colonies between 2002 and 2012. We compared 3 methods of estimating abundance based on count data and calculated mean population growth rates and cumulative probabilities of extinction given the abundance estimates from each method. The first 2 methods of abundance estimation were traditional indices: mean and maximum values of all counts. The third method was a mixture modeling approach that corrected raw counts by a detection parameter. The results of the traditional indices were characterized by high uncertainty levels as reflected in the wide confidence intervals, which limited their capacity to make predictions about the fate of the populations with any confidence. The mixture modeling method provided more reliable results; there was a 51% probability of populations facing quasiextinction (i.e. ≤20 vultures) in 13 yr and a 99% probability of quasi-extinction in 18 yr. Because the mixture modeling method provided more precise predictions while requiring minimal additional effort, population biologists using count data are encouraged to employ such model-based estimators. The white-rumped vulture populations in Rampur are in danger of disappearing within 2 decades, so conservation efforts should be expedited to prevent the loss of this species.

Preference of trees for nest building by critically endangered white‐rumped vultures (Gyps bengalensis) in Nepal

“…Between 2002 and 2022, we recorded the number of nests of white-rumped vultures in the study area following the protocols used by Baral et al (2005Baral et al ( , 2013 and Gautam and Baral (2013). We marked the location of nests, and noted the nesting tree species.…”

“…An in‐depth knowledge of the characteristics of preferred nesting trees and nest survival is key factor in determining the reproductive success of vultures (Chiavacci et al., 2014 ; Francis et al., 2011 ). Predation, natural disasters such as storms, and anthropogenic disturbances such as cutting down the nesting trees and collection of chicks are some reasons for nesting failure in vultures (Baral et al., 2005 ; Baral & Gautam, 2007 ; Keyser, 2002 ; Newton, 1998 ). The availability of large nesting and roosting trees is crucial for vulture survival as they provide a good vantage point to locate food sources and reduce the risk of predation by land animals (Kendall et al., 2018 ; Vogel et al., 2014 ).…”

“…To support the recovery of vulture populations, various conservation programs have been initiated, including captive breeding and release programs, the establishment of vulture safe feeding sites and zones, public awareness campaigns, and the declaration of diclofenac‐free zones (DNPWC, 2015 ). Making sure the availability of suitable nesting and roosting trees in the wild is crucial for the long‐term survival of vultures (Baral et al., 2013 ; Pain et al., 2003 ). However, insufficient information exists regarding what constitutes suitable trees for nesting or roosting.…”

“…Following the significant drop in wild population, the white‐rumped vulture is now found patchily distributed across Nepal (Baral et al., 2005 ; Bhusal et al., 2020 ; Dhakal et al., 2022 ; Gautam & Baral, 2013 ; Rana et al., 2019 ). Despite the effective ban on diclofenac, the species continues to suffer from food shortage, human persecution, unintended poisoning, and habitat destruction (Baral et al., 2005 ; BirdLife International, 2021 ), with the latter being the primary cause of local colony extinction due to habitat loss (Baral et al., 2005 , 2013 ). The choice of tree species for nesting by white‐rumped vultures can vary between sites (Bhusal et al., 2023 ; Ghimire et al., 2019 ).…”

Chi-Square Mixture of Transformed/Inverse Transformed Gamma Family

“…Fields in which mixture models have been successfully applied include, but not limited to, fisheries (Fleischman & Burwen, 2003), economics (Alexander, 2004), medicine (Schlattmann, 2009), genetics (Schork et al, 1996), psychology (Ram & Grimm, 2009), palaeontology (Hunt & Chapman, 2001), archaeology (Dong, 1997), electrophoresis (Melnykov et al, 2011), sedimentology (Sylvester, 2007), geology (Coli et al, 2012), botany (Gutierrez et al, 1995), agriculture (Xu et al, 2010), zoology (Baral et al, 2013), communication theory (Yang & Zwolinski, 2011) and engineering (Liu et al, 2008).…”