The Diurnal Behavior Rhythm And Foraging Habitat Selection Of Wintering Spotted Redshank In Poyang Lake

Poyang Lake is the largest lake in China. It provides wintering sites for more than 400,000 waterbirds, and is regional and global importance for the conservation of migratory waterbirds of the East Asian-Australasian Flyway. Shorebirds are the second largest wintering waterbirds in Poyang Lake, and are important component of the wetland ecosystem. Most shorebirds of the East Asian-Australasian Flyway utilize China coastal areas as stopping or wintering sites. Researches about shorebirds ecology were mostly focused on coastal regions, with few on inland areas. In our study, we selected Spotted Redshank(Tringa erythropus), one of the most abundant shorebirds in Poyang Lake as subject. Our researches were about the diurnal behavior rhythm and foraging habitat selection of wintering Spotted Redshank in Poyang Lake.1. Diurnal behavior rhythm of Spotted RedshankInvestigation of behavior rhythm of wintering birds may help us understand how birds survive in hard winter environment by adjusting behavior and time budget. Until now, most relevant researches were focused on large waterbirds, with little on small waterbirds. Compared with large birds, small birds spend more energy during thermoregulation, which may result in different diurnal rhythm between large birds and smaller ones. In our study, we selected Spotted Redshank, the most abundant small waterbirds in Poyang Lake, as our object. We investigated the time budget of Spotted Redshank at a sub-lake of Poyang Lake(Changhuchi) from November 2014 to March 2015. Our results indicated that foraging was the most frequent diurnal behavior, with average diurnal time-activity budgets of 61.4%. The proportion was higher than many other large carnivorous waterbirds. We think this may be related to the smaller body size of Spotted Redshanks, which makes them suffer more energy loss during thermoregulation. In order to fulfill the daily energy requirement, they have to allocate more time to take more food. The second major behavior was resting, accounting for 32.1% of daylight period. The proportion of time spent on feeding was negatively correlated with that on resting(r=-0.905, n=8, P=0.002), and the trade-off between feeding and resting was critical for Spotted Redshank to survive during harsh winters. Alerting accounted for 0.8% of daylight period, significantly lower than some large waders. The lower proportion may be related to the aggregation characteristic of Spotted Redshank. Over the wintering period, the time budge for feeding reached the peak while resting dropped to the lowest level in January, the coldest month of year. The feeding proportion showed a growing trend during the daytime, while the resting showed an opposite trend. Chi-square analysis results indicated that, although the time budgets of feeding and resting shown a certain degree of variation during diurnal period, the variation was not significant. Feeding mostly occurred in water level lower than the hock of Spotted Redshank(0-5.5 cm), with a proportion of 56.8% of all individuals. Nevertheless, resting was most active in water level higher than the hock(5.5-8.6 cm), with a proportion of 59.8% of individuals. Security and food availability may be the main factors influencing habitat selection of Spotted Redshank.2. Foraging habitat selection of Spotted RedshankWhile most shorebirds in China mainly utilize coastal regions as wintering areas, Spotted Redshank mainly utilize inland regions, with Poyang Lake as the most important wintering area. Exploring possible food sources of Spotted Redshank could help understanding the reasons of the special distribution. From November 2014 to April 2015(wintering period), we investigated the distribution of Spotted Redshanks and collected some core samples of bottom sediments in some sub-lakes of Poyang Lake. During the whole wintering period, we totally collected 68 core samples. Zoobenthos in these samples were divided into 5 categories, including Gastropods, Tubificidae, Hirudinidae, Chironomidae larvae and Psychodidae larvae. Mean comparison indicated that Tubificidae and Chironomidae larvae were the two main groups of zoobenthos in both foraging region and non-foraging region. Nonparametric test(Mann-Whitney U) result indicated that the number of Gastropods(Z=-1.909, P=0.056>0.05), Tubificidae(Z=-0.490, P=0.624>0.05) and Hirudinidae(Z=-0.512, P=0.608>0.05) did not show significant difference between foraging region and non-foraging region, which suggested that these 3 groups of zoobenthos had little influence on foraging habitat selection of Spotted Redshank. The numbers of Chironomidae larvae(Z=-1.971, P=0.049<0.05) and Psychodidae larvae(Z=-2.129, P=0.033<0.05) revealed significant difference between foraging region and non-foraging region, which suggested that Spotted Redshank tend to select the foraging habitat where the density of these 2 groups of zoobenthos is relatively high. Difference in the composition of zoobenthos between coastal and inland regions may be related to the special distribution of Spotted Redshank. However, further researches are needed to prove this deduction.