Population structure, breeding success, and behavior of white-rumped vulture Gyps bengalensis in the Gandaki River Basin, Nepal
Date
2024-04
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Institute of Science & Technology, T.U.
Abstract
Once abundant, the white-rumped vulture (Gyps bengalensis), suffered a catastrophic population decline due to the veterinary use of diclofenac. South Asian countries, including Nepal banned veterinary diclofenac production, distribution, and use in 2006. However, little is known about the population trends on critically endangered white-rumped vulture within the Gandaki River Basin of Nepal. This study investigated the population trends of white-rumped vultures in the Gandaki River Basin through direct observations in the field from 2006 to 2022. This involved total count surveys to record a population size, and the number of occupied nests and productive nests. In addition, the white-rumped vulture behavioral sequences were also assessed during the breeding season using Monte Carlo simulations. This study also explored white-rumped vulture’s tree species preferences for nest building and the factors influencing it. This study found the white-rumped vulture population continuously declining over the past 16 years, despite the veterinary diclofenac ban. The minimum and maximum number of vultures were 54 and 114, respectively. Among the recorded individuals the highest average adult population was 90.23%, and followed by sub-adults, and juveniles. The intrinsic population growth rate was declining (mean-count: β = 0.01, t = 1.04, p = 0.32; maximum-count: β = 0.01, t = 1.04, p = 0.32) during the study period. The population growth was determined by the number of productive nests, which increased 3.7% in the study area. Twenty-four percentage (n = 205) occupied nests remained eggless during the egg laying period, 16.84% (n = 144) nests failed during incubation period, and 11.23% (n = 96) in fledgling period. The breeding success i.e., fledging of chicks from the nest was influenced by precipitation, and average maximum and minimum temperature. The behavioral sequence of white-rumped vulture indicated that they spent > 70% time in breeding activities and exhibited predatory behavior. The white-rumped vultures built nests on 18 tree species in the study area. The kapok/silk cotton tree (Bombax ceiba) was the preferred one for nest construction (χ2 = 115.38, df = 1, p < 0.001) among the available tree species. The nest construction of white-rumped vultures was influenced by specific tree characteristics, such as the number of whorls, canopy spread, and tree height. Unfortunately, human activities in infrastructure development and commercial logging of the nesting trees decreased the availability of large and matured trees in nesting sites for the white-rumped vultures. This study found that the major cause of the decrease in the nesting colony was the destruction of its nesting trees. This study indicates that veterinary diclofenac is not only the major determining factors for white-rumped vulture population decline. Other factors, such as low breeding success, potential disruptions in behavioral patterns, and critical nesting habitat loss posed additional threats to the white-rumped vulture population in the Gandaki River Basin. Based on these findings, this study recommends prioritizing the conservation of kapok trees, a preferred nesting habitat for white-rumped vultures. These baseline data can be used for developing site-specific conservation strategies to increase vulture population sizes.
दक्षिण एसियामा व्यापक रूपमा फैलिएका डंगर गिद्ध (Gyps bengalensis) को संख्या तिव्र रूपमा घट्नुमा पशु उपचारमा प्रयोग हुने डेक्लोफेनेक औषधीको असर थियो । वि.सं. २०६३ (सन् २००६) मा यस औषधीको उत्पादन र प्रयोगमा छिमेकी देशसहित नेपालले प्रतिबन्ध लगायो । यस अध्ययनले प्रतिबन्ध पछिको अति संकटपूर्ण रूपमा रहेको डंगर गिद्धको दीर्घकालीन संख्याको अनुगमन, प्रजनन सफलता र पर्यावरणीय अवलोकनका बारेमा गण्डकी जलाधारमा अनुसन्धान गर्ने लक्ष्य राखेको थियो । वि.सं. २०६३ देखि २०७९ सम्म (सन् २००६ देखि २०२२) गण्डकी जलाधार क्षेत्रमा डंगर गिद्धको दीर्घकालीन संख्याको अनुगमन, प्रजनन सफलता र पर्यावरणीय अवलोकनका साथै गिद्धको व्यवहारमा गणितीय प्रयोग पनि गरियो । डंगर गिद्धले गुँड लगाउने रुखको पहिचान गरी गुँड लगाउने रुखका विशेषताहरूको बारेमा पनि अनुसन्धान गरिेएको छ । बिंगत १६ वर्षको अध्ययन अवधिभर डंगर गिद्धको संख्यामा गिरावट रहेको देखियो । डंगर गिद्धको औसत निम्नतम संख्या ५४ र अधिकतम संख्या ११४ रहेको पनि पाइयो । जसमध्ये उच्चतम ९०.२३% वयस्क र क्रमैसँग अल्प–वयस्क र किशोर रहेका छन् । डंगर गिद्धको संख्याको प्रतिगमन वृद्धिदर (औसत गणना विधि ( =०. ०१, t = १.०४, p = ०.३२ र अधिकतम गणना विधि ( = ०. ०१, t = १.०४, p = ०.३२) स्थिर रहको देखियो । प्रजनन सफल गुँडको ३.७% वृद्धिले डंगर गिद्धको संख्यामा असर पा¥यो । डंगर गिद्धका २४% (n = २०५) गुँड बनाउँदा, १६.८४% (n = १४४) ओथारो बस्दा र ११.२३% (n = ९६) बच्चा उडाउने बेलामा प्रजनन असफल रह्यो । डंगर गिद्धको प्रजननलाई वार्षिक वर्षा र औषत न्यूनितम तापक्रमले असर पा¥यो । प्रजननको समयमा डंगर गिद्धले धेरै समय (> ७०%) सन्तानको रेखदेखमा व्यथित गरेको पाइयो । डंगर गिद्धले जम्मा १८ प्रजातिका रुखमा गुँड बनाए पनि सिमलको रुखलाई अधिकतम प्रयोग गरेको भेटियो । यसरी गुँड बनाउँदा जमिनबाट पहिलो अग्लो हाँगा र धेरै हाँगाहरू भएको रुखहरूलाई रोजेको पाइयो । अव्यवस्थित भौतिक संरचना र रुख कटानहरूले गर्दा डंगर गिद्धले आफ्नो गुड लगाउने स्थानहरूलाई असर गरेको भेटियो । जसले गर्दा डाइक्लोफेनेक प्रतिबन्ध पछि संख्या घट्नुमा प्रजननमा अवरोध, गुँड बनाउने रुखहरूको क्षति हु्नु पनि यो गिद्धको संख्या घट्नुको प्रमुख कारण हो । डंगर गिद्धले गुँड बनाउने सिमलका ठुला रुखहरुको संरक्षण र विषाधिमुक्त सिनोको प्रयोगले यस गिद्धको लामो समयसम्म बाच्ने आधार खडा गर्ने छ । यस्ता दीर्घकालीन अध्ययनले डंगर गिद्धको प्रजाति र स्थान विशेष संरक्षण रणनीतिहरुको आधार स्थापित गर्ने छ भन्ने कुरालाई सारको रूपमा प्रस्तुत गरिएको छ ।
Description
Keywords
Conservation, Critically Endangered Species, Nesting Habitat, Predatory Behavior, Population Trend, Scavengers