Comparison of the vocalization starting time among Brown-eared Bulbul <i>Hypsipetes amaurotis </i>in Oiso, Sendai and Miryang, and estimation of light intensity at starting vocalization in Oiso
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- ヒヨドリ<i>Hypsipetes amaurotis </i>の鳴き出し時間のバラツキ比較 （大磯、仙台、密陽）と鳴き出し時刻の照度推定
- ヒヨドリHypsipetes amaurotisの鳴き出し時間のバラツキ比較(大磯、仙台、密陽)と鳴き出し時刻の照度推定
- ヒヨドリ Hypsipetes amaurotis ノ ナキ ダシ ジカン ノ バラツキ ヒカク(オオイソ 、 センダイ 、 ミツヨウ)ト ナキ ダシ ジコク ノ ショウド スイテイ
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Abstract
<p>From July 2014 to March 2016 the data from the vocalization starting times and the frequency of vocalizations thereafter was collected at Oiso Hill in Kanagawa Prefecture. The sounds were amplified and heard using headphones and the data of the vocalizations were recorded on a computer. Automatic recording was also used. Twice a year there was a change in the Bulbuls’ vocalization starting time at sunrise which correlated to the stating time of the civil twilight. Vocalization frequency was determined at one-minute intervals from the start of vocalization to 90 minutes after sunrise. The frequency changed with each season with a high rate (80%) during the breeding season (May and June) and during the non-breeding season in winter (November to February) with a decrease in March (about 40%) and in July and August (about 55%). Throughout the year they didn’t stop vocalizing even after other bird species had stopped singing 30 minutes after they had begun.</p><p>Also, comparing the starting time of vocalization of Bulbuls at sunrise in Sendai and Miryang (Korea), on the average Bulbuls in Oiso began to vocalize earlier and with less variation. This is because there were a higher density of the Bulbuls in Oiso whose habitat is a forest whereas habitat in Sendai and in Miryang are an urban and an agricultural area, respectively, and a broader audible area in Oiso monitored by the amplified sounds. These increased number of the Bulbuls observed contributes to their average earlier vocalization starting time with less variation, statistically. It means that it is important to select a habitat with a higher density and to adopt a method of a wider audible area when surveying the vocalization starting time of birds.</p><p>The horizontal light intensity during the breeding and non-breeding seasons in a natural environment along with the weather and vocalization starting time of Bulbuls was estimated. The results showed that the light intensity during the breeding season (May to July) was 18±22.7 Lx and during the non-breeding season (January to February) was 13.4±6.3 Lx. It appears that the light intensity is related to the circadian clock and the photoperiodism which determines the daily vocalization of the Bulbuls.</p>
Journal
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- BINOS
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BINOS 23 (0), 1-17, 2016
Wild Bird Society of Japan Kanagawa Branch
