Effective Half - Strip Width Of Line Transect And Distribution Pattern Of Forest Birds In Guangdong Province

Birds are often monitored as target species to evaluate biodiversity because of their wide distribution,ecosystem functioning,and easy of sampling.The line transect method survey is commonly used to estimate population density of birds.As sampling errors associated with the survey can bias the estimate,there have been numerous studies to identify the errors and take account for them in the estimation of population density.The width of the sample line was one of the factors that can significantly affect the estimation of bird density in the survey.When the width of the sample line was set larger than the effective half-strip width（ESW）of the bird,the effective area of the bird density calculation was too large and the density of the bird was underestimated.If the sample line width was too small,the recorded data of the birds at the time of calculation will be too small,and the survey results will be incomplete.As a software for density analysis,there were few studies on the results of ESW in Distance software.Through the analysis of 49,788 forest bird records accumulated in Guangdong Province from 2000 to 2017,we explored the relationship between population density and the ESW of different birds to provide a theoretical basis for obtaining accurate line widths of birds in the line transect method and to reduce the bias in the estimation of population density.We also predicted the range of bird distribution with the Maxent model,to analyze the distribution and the total number of birds in Guangdong Province.The main findings were as follows:1.The number of birds’recorded（obs）was the main factor affecting the choice of function combinations in the Distance software.When the number of records was less than20,the Uniform with Cosine adjustments was selected as the best model function combination,but the Distance’s predicted detection function graphics were not working well.As the amount of data increased,each series expansion of the key function Hazard-rate performed better.We recommend using the Uniform with cosine,Half-normal with Cosine,and Hazard-rate with Cosine,Simple polynomiall,Hermite polynomial in the Distance software for analysis.When the number of records was more than 20,especially over 35,the result of different function combinations’CV was smaller and the result was more reliable..2.A total of 175 species in 42 families were observed.There were 52 species of bird with ESW≤25 m,60 species with 25 m<ESW≤50 m,63 species with ESW>50 m.Body length（BL）was significantly positively correlated with ESW（r=0.518,P<0.01）.For birds with larger BL,the effective width was larger,and the formula of ESW=2.14×BL^0.9398（unit:ESW:m,BL:cm）was obtained.The behavior of birds can also significantly affect the effective width.The effective width of birds frequently tweeting was 1.628times larger than infrequent tweeters.3.The Maxent model obtained a total of 191 distribution predictions of birds with a record number more than 5,and the values of AUC（area under curve）show the prediction results were good.Through superposition the distribution areas of 191 species bird,among the 224865 grids divided into Guangdong Province（Average grid area:0.7871 km²）,the highest number of species in the year was 187.The average density of birds was 1453.02±1300.98/km²,and the total abundance of birds in the Guangdong Province was 2.57×10⁸individuals（2.23×10⁸³.00×10⁸ individuals）.Among them,the distribution area and quantity of some rare birds were also obtained.4.The species,density and diversity index of birds increased with forest cover and agricultural land,which as the main land cover of Guangdong Province,and reached the highest in the northern Nanling area.In addition.In addition,although the urban/construction land was not large,it had a significant impact on each index,and the index of urban/construction land had a cliff-like decline.Among them,the number of species in spring was the most abundant,and the other seasons were not much different.The Shannon-Werner index and the Simpson index in spring were the highest in the year.Although the two diversity indices in winter were the lowest,the density of birds in winter was the highest in a year,and the density of birds in summer was the lowest,but the Pielou’s index was the highest.