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Analysis of Bird Count Series by Local Regression to Explore Environmental Changes

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  • 局所回帰による時系列の分解から明らかになった野鳥羽数の環境要因変化との関連性
  • キョクショ カイキ ニ ヨル ジケイレツ ノ ブンカイ カラ アキラカ ニ ナッタ ヤチョウ ハスウ ノ カンキョウ ヨウイン ヘンカ ト ノ カンレンセイ
  • 局所回帰による時系列の分解から明らかになった野鳥羽数の環境要因変化との関連性

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Abstract

Five bird count series observed on a monthly basis from 1967 to 1998 at Jiyu-Gakuen, Higashi-Kurume in Tokyo are simultaneously analysed. Each count series is decomposed into three components, "long trend", "short trend" and "irregular" by two step loess smoothings. This decomposition explains well the relationship between the bird count and some of environmental changes. By selecting appropriate locations and scales as well as the smoothing parameters so as to minimise the residual sum of squares, it is shown that each five long trend very similarly moves with one of environmental factors. Turtledove (Streptopelia orientalis), Browneared Bulbul (Hypsipetes amaurotis) and Great Tit (Parus major) increased its number to link with the enlargement of housing area. Tree Sparrow (Passer montanus) and Gray Starling (Sturnus cineraceus) gradually decreased its number to link with the decrease of open field. Such two bird groups are well described by the environmental preferences. Variation of each short trend can be explained by the effects of breeding season or winter wandering. The fact that each irregular series has no significant trend and very low correlation coefficients suggests a success of our decomposition.

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