Nest-site Selection Of The Little Ringed Plover And Black-winged Stilt

From April to July,2007,the nest-site selection of the Little Ringed Plover(Charadrius dubius) and Black-winged stilt(Himantopus himantopus) were surveyed by direct observation and sampling method in yeyahu wetland.Black-winged stilt is listed in the directory of terraneous wildlife which are protected by the state and are profitable,ecomomical and researchable.The bird is also listed in the directory of migrant birds protected by China and Japan.In china,the breeding habit of this bird was studied respectively by Zhang Yan-Wei,Yang Xue-Ming,etc. There were also some reports of the bird abroad about variation of mercury contamination in chicks,parasitology,molecular ecology,etc.Yet,there has been no work about nest site until now.A total 47 of nests of Black-winged stilt were found,29(61.7%) on island and 18(38.3%)on banks.The bird are more likely to place their nests on island.The bird arrived in yeyahu in April 6 this year,laid their eggs between early May and the end of June.The biggest clutch size is 4,5 was not found.The smallest distance of nests is 4.0 m.The nests were on the ground and have the shape of a shallow plate, the materials were a lot of hays around the nest sites.The minimum and maximum of distance to water is 5.0m,83.3m.The average of diameter of longer,shorter nest axis,depth were respectively 16.11±3.97cm,8.85±1.73cm,1.97±0.65cm.Totally 138 eggs were measured,The average of diameter of longer,shorter egg axis,weight were respectively 44.34±2.11m,30.96±1.07mm,20.01±1.91g.Principal component analysis(PCA) was used to determine the variables that might affect the nest-site selection of the birds.Independent-samples t test was used to find which variables were important.Main factors which affected the nest selection of this bird are: density,overall coverage,height,proportion of hay,distance to water,etc.Refuge are the most critical.Stable temperature,water and food are very important too.T test of 47 nest site and 47 contrastive samples was shown that there are no significant differences in vegetation density and coverage,there are highly significant differences in average height(P＜0.01),distance to water(P＜0.01), proportion of naked ground(P＜0.01),proportion of hay(P＜0.01).This bird are more likely to choose habitats with the following conditions:higher vegetation, higher proportion of hay,farther from human activity,nearer to water,but lower proportion of naked ground than the 47 contrastive samples.T test of 18 nest site samples on bank and 29 on island was shown,there are highly significant differences in density(P＜0.01) and coverage(P＜0.01) of vegetation,distance from interference sources.There are no significant differences in distance to water and water content of soil surface.There are significant differences in proportion of hay(P＜0.05).Compared with samples on bank,there are lower in density,coverage,species richness,height;but higher in proportion of hay and proportion of naked ground.Although distance to human activity is relatively nearer,but a man was not able to reach the island without a boat,and fishing is forbidden in yeyahu in law.So we can regard proximately no interference exist on island.Furthermore,food and water are more convenient.The colors of eggs and little birds are similar to the colors of hay around nests,which play the same role to vegetation refuge.Higher proportion of hay and naked ground can help eggs absorb enough solar energy.So we can easily see why Black-winged stilt had a highly greater tendency to nest on island.The Little Ringed Plover belongs to Charadriiformes,Charadriidae, Charadrius.And is listed in the directory of terraneous wildlife which are protected by the state and are profitable,ecomomical and researchable.The bird is also listed in the directory of migrant birds protected by China and Austrilia.In china,the breeding habit of this bird was studied respectively by Zhang Qing-Xia,Du Ai-Ying,Wang Hai-Chang,Wu Jian-Dong,etc.There were also some reports of the bird about parasitology abroad.There has been no special work about nest site until now.The Little Ringed Plover arrived in yeyahu in early April and started laying in early May.A total 45 of nests were found,28(62.2%)along the bank and 17(37.8%) on the island.The bird had a significant tendency to place their nest along the edge of bank.Characteristics of each nest was measured.The nests are on the ground and have the shape of a shallow plate,the malerials are some hays,shells of snail and oncomelania,etc.The average of diameter of longer,shorter nest axis,depth were respectively 9.02±1.45cm,6.01±0.90cm,1.80±0.48cm.Totally 147 eggs were measured,the average of diameter of longer,shorter egg axis,weight were respectively 29.46±0.99mm,22.01±0.57mm,7.48±0.49g.The smallest distance of nests was 3.8m.The minimum,maximum of the distance to water is 5.0 m,300.0m.The biggest clutch size is 4.Laying eggs was first seen in May 2.The main factors which affected the nest selection of this bird are:vegetation coverage,plant species richness,vegetation density,the biggest vegetation height,distance from interference sources(roads),average vegetation height,water content of soil, distance to water,etc.T test of 45 nest site and 45 contrastive samples was shown there are significant differences in vegetation density and coverage,species richness;there are highly significant differences in Proportion of naked ground;there are no significant differences in other variables.This bird are more likely to choose habitats with the following conditions:greater species richness of vegetation and greater proportion of naked ground,but lower vegetation density and coverage than the contrastive samples.Too dense plant will prevent the birds from finding prey and moving freely and this is disadvantageous to egg incubation.In yeyahu,eggs incubation of the Little Ringed Plover depends on solar energy most time in sunny days.And few nest exists in such sites.If an area is too sparse,the bird will prefer the site which has many shells to nest to bewilder enemy and human.This kind of protection plays the same role to vegetation refuge.T test of 18 nest site samples on bank and 29 on island was shown,there are highly significant differences in density,average height,maximum height and species richness of vegetation,distance from interference sources,coverage is very higher too.Although distance to human activity is relatively nearer on island,but a man was not able to reach island without a boat,and fishing is forbidden in yeyahu in law.So we can regard proximately no interference exist on island.On the contrary the Little Ringed Plover had a significant tendency to nest on banks.Comparison tells us that density and species richness of vegetation,insect food accordingly on bank are much higher than nest-sites on island,it is why Little Ringed Plover are more likely to nest here.We can see refuge and food is most critical in nest-site selection.The result of t test is in accord with PCA.Refuge,food,water and disturbance are the basic factors in habitat selection. Refuge is the most important.Besides nest site must provide a stable heat for incubation.Competition is very important too.In this paper,competition and the coexistence in nest-site selection of the two species was considered.Food,water,reproductive season length and reproductive peak,nest location,nest material overlapped in the two species.Obviously competition exists between them.t test was showm Black-winged stilt tend to build nests in the areas with the following conditions:higher vegetation with higher coverage and density,nearer to water,bigger Proportion of hay.While the Little Ringed Plover like to nest in areas:Lower vegetation with lower coverage and density, farer away from water,lower Proportion of hay.Characteristics of their nests were distinctly different.The coexistence mechanism of them is nest-site differentiation.The major threats to waterbirds habitat in yeyahu were drought,fishing,farming in light of which,corresponding protection measures were put forward.