Population Fluctuation and Spatial Distribution of Little Egrets Egretta garzetta in the Zenkoji Plain
| Autor: | Kenzo Haneda, Aya Iwasaki |
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| Rok vydání: | 1982 |
| Předmět: | |
| Zdroj: | Japanese Journal of Ornithology. 31:41-56 |
| ISSN: | 1881-9702 0040-9480 |
| DOI: | 10.3838/jjo1915.31.41 |
| Popis: | (1) The distribution and the population fluctuation of Little Egrets Egretta garzetta in the Zenkoji Plain, Nagano Pref., were studied in 1978-81.(2) The colonies and roosts of Little Egrets were situated along the Chikuma River, which passes through our study area. Each of the roosts was used at a given time of the year and the use of the roosts was regular each year.(3) The number of Little Egrets increased rapidly after their breeding and then decreased gradually toward the next breeding season. The population increase after breeding season has, however, diminished with a yearly increase of the number of breeding birds.(4) In the breeding season distribution of Little Egrets in the daytime was concentrated around their colony. However, their distribution expanded throughout the study area soon after their breeding.(5) In the breeding season feeding took place within the radius of 7 to 13 km from their colony. The farthest feeding point from the roost was 7.4 km in the non-breeding season.(6) The overlap of feeding areas between the members of different colonies was not observed. In the non-breeding season some overlap of feeding area was observed between the members of different roosts. No significant correlation was found between the size of colony and their feeding areas.(7) The authors discussed some reasons why the number of Little Egrets increased in the Zenkoji Plain and the number of breeding birds decreased after yearly increase of the Egret population, and the factors influencing the breakup of roosts after breeding. |
| Databáze: | OpenAIRE |
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