Asian Herpetological Research 2011, 2(1): 36-40 DOI: 10.3724/SP.J.1245.2011.00036 Nest-site Use by the Chinese Alligator (Alligator sinensis) in the Gaojingmiao Breeding Farm, Anhui, China Jianjun WANG1, Xiaobing WU1*, Dawei TIAN1, Jialong ZHU2, Renping WANG2 and Chaolin WANG2 1 Anhui Provincial Key Laboratory for Conservation and Exploitation of Biological Resources, College of Life Sciences, Anhui Normal University, Wuhu 241000, Anhui, China 2 Anhui Research Center for Chinese Alligator Reproduction, Xuanzhou 242034, Anhui, China Abstract Nest-site and nesting material used by the Chinese alligator (Alligator sinensis) was studied at the Gaojingmiao Breeding Farm, Langxi County, Anhui, China from May to September 2009. In this study, artificial nesting materials were placed in 43 potential nesting sites before the nesting season, 11 of which were used. Additionally, eight nests were built at natural sites without artificial nesting materials provided. Seven environmental variables were measured at each nest site: distance from water, height from water surface, sunlight duration, nearest bank slope, nest site slope, vegetation coverage and concealment. Statistical analyses indicated that concealment was significantly different between used and unused nest sites, with concealment being significantly correlated to the use of materials- placed sites. In comparing the nests at artificial vs. natural sites, only the nearest bank slope differed significantly. Further, principal component analysis of natural nests indicated that the duration of nest exposure to sunlight and vegetation coverage were more influential than the other factors studied. Keywords Chinese alligator, nesting, artificial nest, natural nest, habitat use, reintroduction 1. Introduction late June to early July (Chen et al., 2003), where nests are The Chinese alligator (Alligator sinensis) is a rare built on the banks of ponds. Nests are usually made with archosaurian reptile endemic to China and is one of the plants, such as Miscanthus sinensis, Cynodon dactylon, most endangered of the 23 extant crocodilian species and Imperata cylindrical var. major (Chen et al., 2003). (Jelden et al., 2002). Wild Chinese alligator populations Nesting ecology has been studied for several species have shown a steady decline over the last century (Chen of crocodilians (Joanen, 1969; Webb et al., 1977; Metzen, et al., 1979; Ding et al., 2004; Wu et al., 2008). Releasing 1977; Magnusson, 1978; Crawshaw and Schaller, 1980; captive-bred Chinese alligators into wild field locations Dietz and Hines, 1980; Wilkinson, 1983; Lutz, 1984; Hall (i.e., reintroduction) is an effective way to repopulate and Kushlan, 1987; Frank, 1989). Previous studies of A. wild communities (Jiang, 2004). An important aspect of sinensis nesting ecology found that the weather in the area reintroduction is to ensure the success of reproduction and moisture of the nesting material affected the nesting for individuals released into the wild. Nest site selection time and egg-laying time respectively (Xia and Jiang, is a key component of nesting success, and thus directly 2005), the level of vegetation canopy and the distance to affects the fitness of the reintroduced individuals in the water also affected the selection of nesting sites (Zhang populations. A well studied nesting period occurs between et al., 2006), those sites with vegetation coverage of 63% to 88% were suitable for A. sinensis when nesting (Zhou, 2007). However, all the above studies were restricted to the captive-bred Chinese alligators, which may behave * Corresponding author: Prof. Xiaobing WU, from the College of Life Sciences, Anhui Normal University, with his research focusing on the differently from the alligators in the wild. This study was conservation genetics, ecology and molecular systematics of endangered conducted in an area near the reintroduction locality for species. E-mail: [email protected] A. sinensis, where the habitat is similar to that found in Received: 28 June 2010 Accepted: 4 March 2011 the wild. Using the data from environmental variables No. 1 Jianjun WANG et al. Nest-site Use by the Chinese Alligator (Alligator sinensis)... 37 collected at the studied nest sites, we analyzed the factors (tested by One-sample Kolmogorov-Smirnov Test), that affected the nesting of A. sinensis, aiming to provide differences were compared by independent-samples t-test support for improving reintroduction habitats through in each group. Categorical data were compared by Chi- better nest site selection for reintroduced individuals. square test in each group. Furthermore, the variables with significant differences in each group were tested 2. Methods by logistic regression to determine correlation. Finally, principal component analysis (PCA) was performed on The study was conducted at the Chinese Alligator the variables of natural nests, and we retained only those Gaojingmiao Breeding Farm (31°01′N, 119°12′E), with eigenvalues greater than 1.0. which is located within the Gaojingmiao Forestry Farm in Langxi County, Anhui, China. This area (Figure 1) is surrounded by a 2.1 m-high iron fence and consists of 8 natural ponds. Each pond has a sluice to maintain a stable water level (depth of 1.5 m). The ponds are surrounded by vegetation, mainly composed of Robinia pseudoacacia, Ligustrum lucidum, Pterocelis tatarinowii, Rosa multiflora, Rubus parvifolius and Pleioblastus amarus (Zhou et al., 2004). The Farm has an annual mean temperature of 15.9 °C, and annual mean precipitation of 1,294 mm (Wu et al., 2008). 211 adult Chinese alligators, introduced from the Anhui Research Center for Chinese Alligator Reproduction (ARCCAR), were raised in the Figure 1 Map of the Gaojingmiao Breeding Farm of Alligator eight ponds of the Farm with a sex ratio of 3 females: 1 sinensis and the location of three types of nesting sites. male and 0.024/m2 population density. The snout-vent length (SVL) of the introduced Chinese alligators ranged 3. Results between 64–79 cm and the age between 9–11 years. In late May 2009, workers of ARCCAR placed Nests were constructed at 11 of the 43 sites with articifial supplemental (artificial) nesting materials at 43 possible materials (named as artificial nest) and 32 were unused nesting sites based on their experience. In early July, (named as unused site) by Chinese alligators. Additionally, we watched pond banks daily at 12:00–14:00, when the eight nests were built at sites without artificial nes- Chinese alligators avioded sunlight by staying in the water ting material (named as natural nest). All the sites were (Zhang et al., 2006). Seven environmental variables were measured by GPS, and showed in Figure 1. The characte- measured at each nest site: distance from water (m); height ristics (mean±SD) of each type of nesting sites are shown from water surface (m); sunlight duration (h, average time in Table 1. of sunlight in one day, recorded by authors from June The differences in the variables were compared to July); nearest bank slope (°); nest site slope (slope of between used sites (artificial nests) and unused sites. nest bottom, measured by comparison of goniometer, and Significant differences were not found in most of the divided into four grades, 1: 0–5°; 2: 5–10°; 3: 10–15° and variables except concealment (X2 = 33.121, df = 3, p = 4: 15–20°); vegetation coverage (percentage of vertical 0.000; Table 1). Furthermore, the results of the logistic projection of plant above the nest to nest area, and divided regression indicated that concealment was significantly into four grades by the percentage of vegetation coverage, correlated with the use of materials-placed sites (Wald = 1: 0–25%; 2: 25%–50%; 3: 50%–75% and 4: 75%–100%); 8.784, df = 1, p = 0.003). Examination of the difference and concealment (divided into four grades by distance to between artificial and natural nests within each variable passage and visible or not, 1: short distance and visible; 2: indicated that only the nearest bank slope had significant short distance and invisible; 3: long distance and visible difference (p = 0.13; Table 1). and 4: long distance and invisible). PCA on the environmental variables of natural nests We used sine transformation for the data of the nea- extracted two principal components accounting for 72.1% rest bank slope. We did comparisons in two groups: used of the variance (Table 2). The two principal components vs. unused sites and natural vs. artificial nests (i. e., used were extracted to calculate corresponding diagnostic sites). As all the numerical data were normally distributed vector for each variable (Table 3). The results indicated 38 Asian Herpetological Research Vol. 2 Table 1 Characteristics of each type of nesting sites and probable differences in each comparison Variable Mean ± SD Difference Artificial nest Unused site Natural nest Artificial nest vs. Artificial vs. natural (n=11) (n=32) (n=8) unused site nest Distance from water (m) 3.53±0.53 3.70±1.05 4.59±2.69 0.608a 0.218 a Height from water surface (m) 1.08±0.35 1.10±0.27 1.07±0.27 0.905a 0.923 a Sunlight duration (h) 7.00±3.25 8.34±1.93 5.00±3.58 0.106a 0.222 a Nearest bank slope (°) 30.04±9.25 28.71±9.25 46.13±9.25 0.759a 0.013 a Nest site slope 1.55±0.82 1.44±0.98 1.37±0.74 0.153b 0.944 b Vegetation coverage 1.55±1.21 1.34±0.83 2.50±1.31 0.453b 0.059 b Concealment 3.45±1.04 1.44±0.50 3.25±1.16 0.000b 0.097 b a: Compared by the independent-samples t-test; b: Compared by the Chi-square test. Table 2 Eigenvalues from principle components analysis of natural nests Principle component 1 2 3 4 5 6 7 Eigenvalue 3.847 1.200 0.837 0.738 0.293 0.086 0.001 Contribution (%) 54.952 17.149 11.951 10.536 4.180 1.222 0.010 Cumulative contribution (%) 54.952 72.100 84.051 94.587 98.768 99.990 100.000 Table 3 Environmental variables and associated PCA scores of reduce the risk of predation by hiding their nests (Joan natural nests and Bridget, 1996; Frank et al., 1995).