| The Crested Ibis(Nipponia nippon) is one of the most endangered birds endemic to east Asia in the world. During the past 30 years, a great deal of efforts both in-silu and ex-situ conservation has been successfully undertaken by Chinese governments and researchers. Since the 1980s, the population has increased from seven to more than 2000 individuals including approximately 1100 wild individuals inhibited in yangxian County and adjacent areas, and more than 1000 captive-bred individuals resided in 12 protection centers and zoos in China, Japan and Korea. The first reintroduction program of the Crested Ibis was conducted in Ningshan County in May 2007. By 2015,56 captive-bred individuals were released to the wild. A total of 26 breeding pairs have bred successively within the release range. One hundred and seventy one eggs in 53 clutches hatched 124 nestlings and fledged 88 young successfully. The results indicated that the first reintroduction program in the world has achieved one of its first targets.In order to determine the population dynamics and habitat use of the roosting colony, and to provide necessary theoretical and practical basis for the Crested Ibis conservation, flocking patterns and night-roosting site utilizition were investigated using quadrat methods and radio-telemetry from March 2013 to December 2015. The main results are listed as follows.There are 6 settled night-roosting sites were recorded. The Crested Ibis usually gathered in large night-roosting flocks in non-breeding period. Frequency distribution of all types of behavior is random before roosting. The rest behavior (4.72%±2.31%) and the preening behavior (3.54%±1.62%) have the largest proportion. The Crested Ibis have different roosting rhythms during different periods. The activity in breeding period was obviously stronger than the other two periods. There is a significant correlation between daylight and departure-arrival time (P<0.001). The weather conditions has significant effects on arrival time (U=1.4, Z=-1.467, P=0.006), but had no significant influence on departure time (U=1.2, Z=-1.381, F=0.005).The wild conut showed that there are significant different in maximum number of flocking individuals among years and months. The proportion of the three largest groups by the total number of individuals is 53.66%,45.24% and 40.42%, respectively. The minimum colony number was recorded in July. There is no significant different in night-roosting site utilization ratio among years (F=1.103, df=2, P=0.485) and months (F=0.026, df=6, P=0.295) with the the maximum proportion in December, and the minimum proportion in July.Principal component analyses for the 6 roosting quadrats indicated that the vegetation is the most important factor affecting the roosting site selection with the contribution ratio of 31.033%, following by the roosting tree with the contribution ratio of 27.014%. The Crested Ibis has obviously selectivity for the roosting habitats where they exhibit preference to mixed coniferous and broad leaved forests as the roosting site. The difference between tree density and forest area was significant (t=3.112, df=68, ;P=0.008), where the tree density is the principal factor (Wilks1 Lambda=0.386, F=36.471,/M).000).There are 13 roosting trees consisting of 6 species in roosting site. Analysis revealed that the Crested Ibis prefer to choose Masson Pine (Pinns massoniana) as the roosting tree (%2=37.346>x20.01=17.792, df=5, P<0.001), with the maximal utilization rate of 63.54%, following by Acer Monoes (Acer elegantulum) with the utilization rate of 17.85%. Most other species are as the temporal roosting trees. The diameter at breast height and height of roosting tree are the most important factors affecting the roost tree selection (Wilks1 Lambda=0.164, F=13.79, P=0.001; Wilks1 Lambda=0.365, F=45.217, P=0.005). Comparing with other trees in roosting sites, the roosting tree have significant larger diameter at breast height and height.The loose foraging groups occurred in daytime and larger night-roosting flock occurred at night. From November 2013 to January 2014, April to June in 2014 and July to October in 2015, under investigation the numbers and the colony of the Crested Ibis in different sample habitat statistical showed that:the sample I (Zhaigou village) and sample Ⅲ (Zhujiazui village) have a large numbers and colony. While the sample IV (Fengliu village) have a small numbers and colony.At present, there are three main hypotheses to explain the function of roosting colony-the security center hypothesis, the Information Center Hypothesis and the Recruitment Center Hypothesis. Based on the previous hypotheses, this paper quote another one-the Pair Formation Hypothesis, wich suggest that the roosting colony can provide temporal and spatial conditions to find the potential mates for individuals of different ages and natal sites. The Crested Ibis usually roosts with flocking in the fixed sites. Therefore the synchronous survey in roosting sites is very helpful to determine the population number, age structure and distribution of the Crested Ibis. It can also provide basis for improving management measures and proposing new protection plans to finally establish a self-sustaining population. |
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