由群集數量與取食速率探討樹麻雀(Passer montanus)於水稻田的取食模式

Abstract

樹麻雀（Passer montanus）為群集（flock）覓食的社會性動物，經常於水稻田穀粒成熟期，群體飛至水稻田取食稻穗，造成農民損失。本研究以水稻田為背景，探討樹麻雀於水稻田的取食模式，希望藉由模式預測適時加強防治作業，降低農民損失。本研究於2008-09年於國立中興大學農業試驗場進行實驗，利用平台試驗瞭解樹麻雀於取食稻穀時群集數量與取食速率之關係；群集可以減少個體之警戒頻率並提高取食速率，但隨著群集數量愈多，造成個體所能分配到的食物量減少，使得取食速率又逐漸降低。然而，在食物豐富的情況下，個體之取食速率將不受群集數量所影響；群集數量愈多，個體警戒頻率愈少，取食速率愈快。 除平台試驗之外，本研究也進行水稻田觀察錄影，拍攝樹麻雀於水稻田取食之情況，並計算樹麻雀的群集數量、取食時間與取食頻率，且從水稻抽穗後每週測量稻穗之重量。結合取食速率迴歸線與水稻田錄影數據，估算樹麻雀之取食量，發現樹麻雀每日取食量(Y)與水稻成熟天數(X)成正相關：Y= 0.16X - 1.17 （R2 = 0.76, p<0.05）。由於稻穗在成熟過程中重量會逐漸變重，故以取食的顆粒數來估算樹麻雀對水稻田之危害率，發現於第四週取食顆粒數最多，佔總取食顆粒數57.5％。根據結果顯示，農業試驗場於2009年一期稻作，樹麻雀共取食206.2公斤的稻穗，佔總產量1％，其中水稻抽穗後第四週，危害率最高0.49％。本研究將樹麻雀對稻作的危害進行量化，水稻田愈接近收割，樹麻雀取食量愈多，且在水稻抽穗後第21-28天是危害之高峰期，此時是需加強防治的時段。

Tree sparrow（Passer montanus）is a social animal. They would flock together and flew to the rice fields to forage on grain during rice ripening period result in the loss of production. Considering rice field in the background, understanding for foraging model of tree sparrow studied in this research. The main objective was to reduce the loss of production through the foraging model. We filmed the state of foraging of tree sparrows at the agricultural experimental station of National Chung-Hsing University at Taichung in Taiwan during February to June in 2008. Result detailed about the relationships between flock size and uptake rate through the food patch, where more individuals in a flock recorded lower alert frequency and forage faster. However, uptake rate is reduced due to the limited food supply. Therefore, the uptake rate of tree sparrows didn’t affected by flock size in the state of sufficient food supply. More individuals in one flock reduced the alert frequency and forage faster from foraging. In additional of food patch experiment, the rice grain weight measured every week from the rice heading stage. The data was calculated of flock size、foraging time and foraging frequency through the taped observation data, and combined the data with the result of food patch experiments to predict quantity of grains (kg/ha) did tree sparrows forage at organic rice field per day. The daily rice consumption (Y) and the mature date of rice(X) expresses as Y= 0.16X - 1.17 （R2 = 0.76, p<0.05）. The grains became heavier each day during the ripening period. Weight of the rice grain has changed during the ripening period, therefore, the number of grains consumed by tree sparrows represented the rice damage rate. Tree sparrow foraged the maximum on the fourth week of rice ripening period with an average of fifty-eight percent of all foraging amount. According to this study, the foraging amount of first-crop rice of tree sparrows in 2009 is 206.2 kg with equivalent to one percent of total rice yield. In addition, the damage rate is the most concerning is 0.49％, on the fourth week. We quantified the damage of foraging amount of tree sparrows. The tree sparrows foraged more and more when the ripening progresses. Therefore, current research concluded to take damage control action from the day of 21 to 28 after the rice heading, as it was the time of most serious damage by tree sparrow foraging.