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Fasheng Zou, Qiang Zhang, Min Zhang, Myung-Bok Lee, Xincai Wang, Yuening Gong, Changteng Yang. 2019: Temporal patterns of three sympatric pheasant species in the Nanling Mountains: N-mixture modeling applied to detect abundance. Avian Research, 10(1): 42. DOI: 10.1186/s40657-019-0181-6
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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 White-necklaced Partridge Arborophila gingica) along an elevational gradient, using N-mixture models that take into account imperfect detection in our bird data.
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.
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 camera-trapping 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.
Our results demonstrate that the N-mixture model performed well in the estimation of temporal population 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-temporal 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.
An adult Asian Open-billed Stork (Anastomus oscitans) was observed in the Longjing reservoir of Baise City, northwestern Guangxi Zhuang Autonomous Region on 3 October 2010. It is the first record of this big stork in Guangxi, southwestern China. The Longjing reservoir is located in the Youjiang district of Baise, with a total area of about 200 ha. This reservoir, surrounded by Masson pines (Pinus massoniana), is also a fishpond for local people. The reservoir was draining water to net fishes when we detected this stork. The stork foraged snails and fishes at the edge of the reservoir every noon. It also picked up dead fishes from the net. Sometimes it even bit at the dobbers of fishing nets. Many waterbirds, including the Little Egret (Egretta garzetta), the Chinese Pond-Heron (Ardeola bacchus) and the Grey-headed Lapwing (Vanellus cinereus) foraged for food with this stork. It was the most cautious among these waterbirds. It often stayed on high branches of Pinus massoniana trees. Only after other birds foraged for a long time, did it came down to the reservoir. This stork stayed in the Longjing reservoir for about three days and we never saw it after 6 October.
The Asian Open-billed Stork is a waterbird not difficult to identify, commonly appearing in southeastern Asia, in countries such as Bangladesh, Myanmar, Laos, Cambodia, Thailand, Vietnam and India (Zheng et al., 2002; Robson, 2005; BirdLife International, 2009). The first record of the Asia Open-billed Stork was prepared by a Chinese birdwatcher, Yitian Wang, in Xihu lake, Dali City, Yunnan Province in October 2006. Since its first occurrence in China, the Asian Open-billed Stork had not been recorded during the following four years. The stork has, since then, been recorded three times in southwestern China this year. Six Asia Open-billed Storks appeared in Jinggu County, southwestern Yunnan Province in July 2010 and two were observed in Anshun County, southwestern Guizhou Province in September 2010. Baise City is adjacent to China's Guizhou and Yunnan provinces and Vietnam. The distance from Baise City to Anshun County is about 300 km, as the stork flies. Although the Asian Open-billed Stork is a colonial breeder, resident in India, it usually leaves its breeding place every December (Pramanik et al., 2009). Is it an occasional event for the Asia Open-billed Stork to migrate in exceptional weather, or is southwestern China a potential overwintering area? The questions need more surveys of this bird to be answered.
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