Temporal patterns of three sympatric pheasant species in the Nanling Mountains: N-mixture modeling applied to detect abundance

Background:The reliability of long-term population estimates is crucial for conservation and management purposes.Most previous studies assume that count indices are proportionally related to abundance;however,this assumption may not hold when detection varies spatially and temporally.We examined seasonal variations in abundance of three bird species(Cabot’s Tragopan Tragopan caboti,Silver Pheasant Lophura nycthemera,and Whitenecklaced Partridge Arborophila gingica) along an elevational gradient,using N-mixture models that take into account imperfect detection in our bird data.Methods:Camera-trapping was used to monitor temporal activity patterns of these species at Guangdong Nanling National Nature Reserve from December 2013 to November 2017(4 seasons per year).For abundance analysis(N-mixture modeling),we divided a year into 4 seasons,i.e.3 months per season,and performed the analysis by season.Elevation was incorporated into the N-mixture model as a covariate that may affect abundance.We compared the N-mixture model with a null model(no covariate model) and selected the better model based on AIC values to make an inference.Results:From 24 sampling sites,we obtained 6786 photographs of 8482 individuals of 44 bird species and 26 mammal species.Silver Pheasant was photographed much more frequently and showed higher temporal activity frequency than White-necklaced Partridge or Cabot’s Tragopan.Silver Pheasant was camera-captured most frequently in summer,and other two species in winters.All three species had two daytime activity peaks:between 6:00 a.m.and 10:00 a.m.,and between 5:00 p.m.and 7:00 p.m.,respectively.Our estimated abundance and detection probability from the N-mixture model were variable by season.In particular,all three species showed greater abundance in summer than in winter,and estimated abundance patterns of all three species were more similar with observed cameratrapping counts in summers.Moreover,in winter,elevation had a positive impact on abundance of Silver Pheasant and Cabot’s Tragopan,but not on White-necklaced Partridge.Conclusions:Our results demonstrate that the N-mixture model performed well in the estimation of temporal popu lation abundance at local fixed permanent plots in mountain habitat in southern China,based on the modeling of repeated camera-trapping counts.The seasonal differences in abundance of the three endemic bird species and the strong effect of elevation on abundance of two species in winter were only indicative of variations in spatio-tempora distribution within species and between species.In identifying suitable habitat for endemic pheasants,the positive elevational effect also suggests that more attention should be paid to conservation of areas with higher elevation in the Nanling Mountains.

红外相机技术与其他几种森林鸟类多样性调查方法的比较

为了探讨红外相机技术、网捕法、固定距离样线法和固定半径样点法对森林鸟类多样性调查的有效性和实用性,我们于2011–2016年,用这几种方法调查了广东南岭国家级自然保护区和车八岭国家级自然保护区的鸟类多样性。在南岭,固定距离样线法和固定半径样点法记录鸟类222种,网捕鸟类43种,红外相机拍到鸟类47种;其中1种鸟仅网捕到,6种鸟仅被红外相机拍到,164种鸟仅被固定距离样线法和固定半径样点法记录到。在车八岭,固定距离样线法和固定半径样点法记录鸟类109种,网捕鸟类42种,红外相机拍到鸟类27种,其中9种鸟仅网捕到,3种鸟仅被红外相机拍到,97种鸟仅被固定距离样线法和固定半径样点法记录到。随着鸟类的体重、体长、翅长和跗蹠增加,网捕到的鸟类个体数量减少,鸟类身体大小与网捕到的鸟类数量呈显著负相关;而红外相机拍到的鸟类数量随鸟类的身体大小增大而增加,并且呈显著的正相关。本文的结果显示,网捕法和红外相机技术针对不同类群的鸟类调查效力不同,但都是固定距离样线法和固定半径样点法的有效补充。建议今后开展森林鸟类多样性调查与监测时,尽量采用多种研究方法相结合,以求达到最优的效果。