在食物資源貧乏的季節，動物除了需要更有效率獲得食物資源外，環境中潛在的捕食風險亦是威脅動物生存的原因。 鳥類對於覓食環境的選擇可反映出捕食風險的影響，牠們傾向在捕食風險較小的環境中覓食，也有鳥類將食物搬離發現的地方到較安全的位置才取食。 鳥類也表現出覓食時的時間分配的改變，藉由增加警戒頻度來抗衡捕食風險。 動物活動及覓食在與其體色相近的環境中可降低被捕食者發現及攻擊之機會，而關於鳥類選擇覓食位置的背景顏色仍無直接的實驗證明。 鳥類聚集成群除了可降低群內個體被捕食的機會或增加逃脫的可能性外，成群覓食之鳥類群內之個體花費於覓食的時間提高，亦提升覓食效率。 本研究以麻雀（Passer montanus）做為實驗對象，探討環境及覓食位置的背景顏色、群體效應對於麻雀覓食位置選擇及覓食行為之影響。 本實驗測試假說：（一）在不同環境中的背景顏色，反應不同的捕食風險，會影響鳥類對覓食地點的選擇及其覓食表現；（二）在不同環境中的背景顏色對鳥類選擇覓食地點及其覓食行為、表現之效應，會受成群與否影響捕食風險的影響，並隨之改變。 我在野外捕捉麻雀，實驗時將麻雀分為一隻或五隻，將其帶回實驗室，並各別飼養在籠中過夜後，再進行實驗。 兩組背景顏色方面，採用與麻雀體色相近之迷彩褐色及白色，而地面的背景及盤狀取食區都採相同花樣及材質。 實驗前，我先在地面鋪上背景，再將麻雀放入觀察室，給予麻雀四小時適應時間，且期間僅提供清水不提供食物。 四小時後，將兩取食區放置於背景上，直到麻雀開始覓食於取食區上，則開始兩小時的紀錄觀察。 實驗結果與預期相符合：麻雀會先造訪在背景顏色上較突顯之取食區，而在與體色相近的背景上，麻雀較頻繁地造訪取食區覓食，且停留較長的時間。 在白色背景上的白色取食區上，麻雀停留的時間最短。 然而，在麻雀覓食的時間分配及覓食投資方面，群體效應的影響遠大於背景顏色；成小群之麻雀平均花費於覓食行為的時間較少，且其覓食效率高於單獨覓食之麻雀。 麻雀傾向選擇與體色較接近之背景顏色，相較於取食區，周圍的環境更為重要，可能是因為當掠食者接近時，周圍的環境是立即的躲避位置。

Animals’ behaviors often reflected trade-offs between benefit and cost, and both the predation risk and energy provided from food can influence animals’ foraging decisions. Birds foraging in places where the background color is similar to theirs body color, may face lower probability of being detected by predators. In flocks, the effects of group may not only decrease the risk of predation, but also increase the foraging efficiency. This study investigated that the effects of background color, color contrast, and flocking size on birds’ feeding site selection and foraging behaviors. I tested two hypotheses: (1) the risk of predation associated with different feeding sites, indicated by background color and color contrast, will influence foraging decisions and behaviors of ground-foragers’ in feeding. (2) ground-foragers foraging in flocks face a lower risk of predation, which will diminish the effect of background color and color contrast. I caught tree sparrows (Passer montanus) in field, and used two colors for the background and feeding patch, respectively. The first one is camouflaged brown that mimic sparrows’ body color, and the other is white. Each sparrow was herd and fed independently in a birdcage overnight, and then was released into the aviary for feeding experiments. Sparrows were separated into groups of five birds and one bird.
Sparrows tended to be attracted more by conspicuous background color, and often arrived first at the showy patch to feed. However, the sparrows visited frequently and stayed longer on feeding patches on the camouflaged brown background, and stayed the least time on white feeding patches on the white background. Sparrows also visited the camouflaged brown patch more frequently. They spend less time and visited less frequently the white patch on the white background. Group size appeared to have a large effect than background colors on time budget and investments of sparrows which foraging. These results suggest that birds tended to forage on the background similar to their body color, and the surroundings of patches affect their feeding site selection more significantly, relative to feeding patches. This maybe due to the fact that surroundings are often instant places for birds to flee to avoid predators.

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