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  • 學位論文

果實大小及顏色對食果鳥類食物選擇偏好之影響

Effects of Fruit Size and Color on Diet Preferences of Frugivorous Birds

指導教授 : 丁宗蘇

摘要


食果鳥類在植物種子傳播上扮演了相當重要的角色,而且植物果實特徵會高度影響食果鳥類的取食選擇,其中又以果實大小及顏色被認為是最重要的選擇特徵。本研究籠養四種臺灣低地常見的食果鳥類:白頭翁(Pycnonotus sinensis formosae)(平均喙基寬10.3 mm)、紅嘴黑鵯(Hypsipetes leucocephalus nigerrimus)(平均喙基寬11.3 mm)、五色鳥(Megalaima nuchalis) (平均喙基寬16.2 mm)、及樹鵲(Dendrocitta formosae formosae) (平均喙基寬16.5 mm),分別進行(1)天然果實、(2)人工染色麵糰、及(3)塗色的茄苳(Bischofia javanica)果實三組試驗,來測試這四種鳥類對於果實大小及顏色的選擇偏好,並比較鳥類消化後之排遺種子、人工去除果皮的種子、及完整果實之種子發芽率。結果顯示,當果實直徑超過鳥的喙基寬,就不會被鳥類吞入,只能被啄食。白頭翁偏好小徑級果實(1-6 mm),紅嘴黑鵯與五色鳥偏好中徑級果實(6-11 mm)、樹鵲則喜歡大徑級果實(11-16 mm)。在人工麵糰的大小選擇上,喙基寬較小的白頭翁與紅嘴黑鵯選擇的徑級,顯著小於樹鵲與五色鳥。對人工麵糰的顏色選擇,四種鳥皆較偏好黑色及紅色,最不偏好綠色麵糰。在茄苳果實染色實驗,四種鳥類皆會優先選擇成熟並塗上褐色的茄苳果實,其次是未熟塗上褐色的茄苳果實,再其次為成熟塗上綠色的茄苳果實。完整果實的種子發芽率顯著低於人工去果皮種子與經鳥類消化道之種子的發芽率,而人工去果皮種子與經鳥類消化道之種子的發芽率則沒有顯著差異。研究結果顯示,鳥類能吞食的果實大小上限主要取決於其喙基寬,喙基寬較小的鳥類會偏好較小的果實,喙基寬較大的鳥類偏好較大的果實,但是也可以選擇小果實。鳥類在果實選擇上強烈依賴果實的顏色訊號,而偏好紅、黑色這些野外成熟果實的主要顏色。另外,大部分的植物在未經外力去除外果皮果肉的狀況下,其種子發芽率極低。由以上可以推論,食物的大小及顏色是食果鳥類在選擇食物上非常重要的因子。就植物傳播方面,經由鳥類消化道的種子發芽率顯著高於完整果實的種子發芽率,因此這些鳥類確實具有傳播種子的潛力,扮演了相當重要的果實傳播者角色。

並列摘要


Frugivorous birds play an important role in seed dispersal of plants. Characters of fruits also highly affect the food choice of frugivorous birds. Among various fruit characters, fruit size and color have been considered as most important factors affecting the food choice of birds. The main objectives of this study were to examine the foraging preferences of frugivorous birds on various sizes and colors of foods. I caged four frugivorous bird species that are common on the lowlands of Taiwan, including Lightly-vented Bulbul (Pycnonotus sinensis formosae), Black Bulbul (Hypsipetes leucocephalus nigerrimus), Taiwan Barbet (Megalaima nuchalis), and Gray Treepie (Dendrocitta formosae formosae), and conducted three sets of experiments (natural fruits, cooked dough, and colored fruits of Bischofia javanica) to study their foraging preferences. I also cultured and compared the germination of three types of seeds (defecated seeds, uncoated seeds, and coated seeds) to evaluate the effects of digestion and pecking by birds on seed germination. Results revealed that birds only pecked the fruits larger than their gape widths, instead of swallowing. Lightly-vented Bulbul (gape width: 10.3 mm) preferred fruits of small diameter class (1-6 mm), Black Bulbul (gape width: 11.3 mm) and Taiwan Barbet (gape width: 16.2 mm) preferred fruits of medium diameter class (6-11 mm), and Gray Treepie (gape width: 16.5 mm) preferred fruits of large diameter class (11-16 mm). In selecting cooked dough, Lightly-vented Bulbul and Black Bulbul also preferred smaller dough than Taiwan Barbet and Gray Treepie. All the four bird species preferred black and red dough, and least preferred green dough. All the four bird species preferred brown-colored ripe fruits of Bischofia javanica, secondly brown-colored unripe fruits, and thirdly green-colored ripe fruits. The germination rate of defecated seeds and uncoated seeds was not significantly differed with each other but was significantly higher than coated seeds. I concluded that gape width determines the upper size limit of fruit that birds can swallow, and birds with smaller gape width prefer smaller fruits. However, birds with larger gape width can still eatforage small fruits. In selecting fruits, birds strongly depend on the color signal of fruits and prefer colors of black and red, which are main colors of ripe fruits in the field. Without removing the exocarp of fruit, most of the examined plant species have a very low germination rate of seeds. As above, assume that the size and the color of food determines the factor of choosing for the frugivorous birds. On the scale of plant dispersal, through the germination rate of defecated seeds is obviously higher than the germination rate of coated seeds. Therefore, these birds surely are possessed of the potential of seed dispersal for playing an important part of it.

參考文獻


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