Gravel bars can be critical for biodiversity conservation: a case study on scaly-sided Merganser in South china.

Gravel bars are characteristic components of river landscapes and are increasingly recognized as key sites for many waterbirds, though detailed studies on the ecological function of gravel bars for waterbirds are rare. In this study, we surveyed the endangered Scaly-sided Merganser Mergus squamatus along a 40 km river section of Yuan River, in Central China, for three consecutive winters. We derived the landscape metrics of river gravel bars from geo-rectified fine resolution (0.6 m) aerial image data. We then built habitat suitability models (Generalized Linear Models-GLMs) to study the effects of landscape metrics and human disturbance on Scaly-sided Merganser presence probability. We found that 1) the Scaly-sided Merganser tended to congregate at river segments with more gravel patches; 2) the Scaly-sided Merganser preferred areas with larger and more contiguous gravel patches; and 3) the number of houses along the river bank (a proxy for anthropogenic disturbance) had significantly negative impacts on the occurrence of the Scaly-sided Merganser. Our results suggest that gravel bars are vital to the Scaly-sided Merganser as shelters from disturbance, as well as sites for feeding and roosting. Therefore, maintaining the exposure of gravel bars in regulated rivers during the low water period in winter might be the key for the conservation of the endangered species. These findings have important implications for understanding behavioral evolution and distribution of the species and for delineating between habitats of different quality for conservation and management

Using Species Distribution Model to Estimate the Wintering Population Size of the Endangered Scaly-Sided Merganser in China

<div><p>Scaly-sided Merganser is a globally endangered species restricted to eastern Asia. Estimating its population is difficult and considerable gap exists between populations at its breeding grounds and wintering sites. In this study, we built a species distribution model (SDM) using Maxent with presence-only data to predict the potential wintering habitat for Scaly-sided Merganser in China. Area under the receiver operating characteristic curve (AUC) method suggests high predictive power of the model (training and testing AUC were 0.97 and 0.96 respectively). The most significant environmental variables included annual mean temperature, mean temperature of coldest quarter, minimum temperature of coldest month and precipitation of driest quarter. Suitable conditions for Scaly-sided Merganser are predicted in the middle and lower reaches of the Yangtze River, especially in Jiangxi, Hunan and Hubei Provinces. The predicted suitable habitat embraces 6,984 km of river. Based on survey results from three consecutive winters (2010–2012) and previous studies, we estimated that the entire wintering population of Scaly-sided Merganser in China to be 3,561 ± 478 individuals, which is consistent with estimate in its breeding ground.</p></div

Response curves of environmental variables with highest contribution to occurrence of Scaly-sided Merganser.

<p>Solid line is the mean response curve and dotted lines are ±1 SD.</p

Distribution of Scaly-sided Merganser flocks and gravel bar patches in the 36 km river section of the lower Yuanjiang River.

<p>The red dots indicate 127 Scaly-sided Merganser flocks recorded over three winters.Green points represent houses along the river within a 50 m buffer zone. Areas in dark grey are gravel bars in river and area in light grey are islands.</p

Potential wintering distribution areas for Scaly-sided Mergansers in China.

<p>Red indicates predicted distribution area with high occurrence probability.</p

Surveyed rivers in distribution areas of Scaly-sided Merganser.

<p>From left to right are Li River, Yuan River, Xiu River, Fu River, Xin River, Rao River.</p

Summary of GLMs (predictor variables restricted to three or less) supported by survey data.

<p>* See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127387#pone.0127387.t001" target="_blank">Table 1</a> for definition of terms</p><p>^# interaction term</p><p>^ Maximum likelihood pseudo <i>R</i>^<i>2</i></p><p>Summary of GLMs (predictor variables restricted to three or less) supported by survey data.</p

The study area in Yuan River and its location within the Yangtze River Basin in China.

<p>The study area in Yuan River and its location within the Yangtze River Basin in China.</p