Study On Abundance And Distribution Of Wintering Water Birds And Ecological Habits Of Four Crane Species In Poyang Lake

Poyang Lake was an important wetland in Asian-Australia flyway that inhabit a large number of water birds and many endangered species. The author has done some studies on abundance and distribution of water birds and behavior pattern, foraging behavior, group characteristic, age structure and niche differentiation of four cranes in Poyang Lake during the winter from 2012 to 2015. The results showed as following:1. During the wintering period of 2012-2013 and 2014-2015, the abundance and distribution of water birds were investigated in five regions of Poyang Lake. A total of 76 species belonging to 15 families, 7 orders were recorded. Of the 76 species, Black Stork(Ciconia nigra), Oriental White Stork(Ciconia boyciana), Siberian Crane(Grus leucogeranus) and Hooded Crane(Grus monacha) are listed in the first category of the nationally protected wildlife species. Six species are listed in the second category of the nationally protected wildlife species. Some species have been listed in the IUCN Red Data List, such as the Critically Endangered Siberian Crane and Baer's Pochard(Aythya baeri), Endangered Oriental White Stork, three Vulnerable species and six Near Threatened species. The most abundant species were distributed in the Poyang Lake National Nature Reserve(Acronym PYH) which support 62 species. Twenty-four species were recorded as the dominant or common species during the winter of 2012–2013 and twenty-nine species for 2014-2015. Correspondence Analysis demonstrated that some species showed a preference for one of the regions in Poyang Lake during 2012–2013 and 2014-2015; more specifically, Siberian Crane, Hooded Crane, Oriental White Stork, and Pied Avocet(Recurvirostra avosetta) preferred PYH; Grey Heron(Ardea cinerea) preferred Nanji Wetland National Nature Reserve(Acronym NJ); Common Crane(Grus grus), and Black-headed Gull(Larus ridibundus) preferred East Poyang Lake National Wetland Park(Acronym PY); Ruddy Shelduck(Tadorna ferruginea) preferred Duchang Migratory birds Provincial Nature Reserve(Acronym DC). Generally, a negative correlation was observed between water level and the number of water birds, whereas the number of Podicipediformes was significantly positively correlated with water level in some regions. The main reason for this phenomenon may be that Podicipediformes fed by diving, which increases their preference for areas with deep water; the water level in some sample points was often higher than that in the main lake, since it was artificially controlled. The most popular habitat type for dominant or common species was shallow water.2. The wintering time budget and foraging behavior of Common Crane inhabiting rice fields of Poyang Lake were observed by instantaneous scan and animal focal sampling methods. Common Crane spent most of their time foraging(64.09%), followed by alerting, flying and maintenance behaviors. While foraging behavior increased over early, middle and late wintering stages, the other behaviors gradually declined over the same time period. There was a significant interaction effect among environmental factors on behaviors. Maintenance increased when when daily minimum temperature increased, daily maximum temperature decreased, day length increased and humidity decreased. Foraging behavior increased when day length increased and humidity decreased; and alerting behavior increased when day length increased and humidity decreased. The effect of environmental factors on adult individuals was the same as the overall pattern. There was only one significant impact on the foraging behavior of juveniles. The impact of environmental factors on behavior may be a nonlinear relationship that results in the influence trends changing in different ranges. In terms of the activity rhythms, foraging behavior was always kept at a high level in each daytime period, peaking at 11:00–11:59 h and 17:00–17:30 h. Because the foraging habitat and communal roosting habitat of Common Crane were separated, the foraging peak in the morning was delayed. There was also a large difference in activity rhythms between adults and juveniles, with foraging behavior of juveniles being higher than adults in each observation period. Mean peck rate was(32.06± 0.47) pecks / min, mean step rate was(6.55± 0.35) steps / min, and there was a significant negative correlation between peck rate and step rate. Because the availability of food resources in rice-field habitats decreases gradually over winter, the peck rate of cranes should also decrease gradually over time. To ensure adequate energy supply during the winter, it is likely that Common Crane would change their foraging strategy by increasing the step rate and foraging time. Nearly(1.37±0.04) times and(6.02±0.37) s per unit with interval were used for alerting. Adults spend more time alerting than do juveniles and spend more time alerting when in family groups than in flocks.3. The mean group size was 7.52 ± 2.71 individuals for the White-naped Crane and 8.16 ± 1.37 individuals for the Common Crane during the winter of 2012–2013. While the mean group size was 23.86 ± 10.26 individuals for the Siberian Crane, 6.42 ± 1.63 individuals for the Hooded Crane, 6.09 ± 2.55 individuals the White-naped Crane and 5.55 ± 1.26 individuals for the Common Crane during the winter of 2014–2015. The mean group size during 2014–2015 showed no significant difference among species. The mean family group size of the four crane species was between 2.5 and –2.8 individuals, and no significant difference was found among species. The mean flock size of cranes showed no significant difference among species; however, the flock size of Siberian Crane(84.56 ± 37.64 individuals) was slightly larger than that of the Common Crane(14.97 ± 5.17 individuals). The major group type of the four crane species was the family group, which constituted 63–72% of the group types. Within the family group, the types with two adults and one juvenile, or two adults only, accounted for the largest proportion. The mean group size of these four crane species did not conform to the prediction by alert behavior, while habitat quality may be one of the main factors influencing the group size of cranes.4. The percentage of juvenile was 20.21% for the Common Crane during 2012–2013. The percentage of juvenile cranes was also studied in 2014–2015, it was 12.27% for the Siberian Crane, 14.42% for the Hooded Crane, 16.59% for the White-naped Crane, and 20.46% for the Common Crane. We compared the percentage of juvenile cranes to the normal range, which is 10–15%; the percentage of juvenile Siberian Crane and Hooded Crane was within the normal range, whereas that of juvenile Common Crane and White-naped Crane was above the normal range. The percentage of juvenile Whooping Crane(G. Americana) was 13.9% when its population increased, whereas that of juvenile Common Crane, White-naped Crane, and Hooded Crane was higher than the increasing population of Whooping Crane. The population of Common Crane, White-naped Crane, and Hooded Crane would increase or be stable when predicted in the same manner as that for the percentage of juveniles. In order to implement practices for tha conservation of Siberian Crane, it is omportant to study its population tendency. The percentage of juvenile Hooded Crane has decreased in recent years. The percentage of juvenile of four crane species in Poyang lake showed a sharp decrease from early winter to late winter, this decrease was larger than that of Greater Sandhill Crane(G. Canadensis tabida) from fall to winter.5. The space niche and habitat niche were analyzed in this study. Common Crane was found to have the widest niche among the four crane species. The species that had a wider space niche generally had a wider habitat niche. The main reason for this phenomenon may be the difference in adaptability among these crane species. The niche among four cran species was not highly overlapped; for the space niche were 0.09–0.63 and habitat niche were 0.11–0.57. This suggests that these four species of crane have differentiated in space and habitat niche to some extent. The species pairs that showed a higher overlap in space niche generally alsoshowed a higher overlap in habitat niche.