棲地類型與群體規模對紅鳩之覓食與警戒行為的影響

Effects of Habitat Type and Group Size on Foraging and Vigilance Behaviors of the Red Collared Dove Streptopelia tranquebarica

動物採用群體覓食策略具有降低被掠食風險的利益，是經常被探討的一項議題。但群體規模大小及棲地結構均可能影響動物的警戒與覓食行為表現。本研究藉由開闊棲地與鬱蔽棲地之紅鳩（Streptopelia tranquebarica）覓食群體的行為觀察，來探討棲地類型及群體規模對紅鳩之覓食與警戒行為的影響。結果發現，紅鳩的總覓食時間與啄食次數在兩類棲地均會隨著群體規模的增大而增加。鬱蔽棲地之紅鳩的總警戒時間、警戒頻度與每次警戒持續時間都高於開闊棲地的個體。但警戒行為會隨著群體規模增大而減少的群體規模效應假說（group-size effect on vigilance）僅在鬱蔽棲地受到支持。此外，紅鳩在覓食行為間的總移動時間會隨著群體規模的增大而減少，顯示群體覓食的紅鳩不僅具有降低被掠食風險的利益，也可能存在增加覓食效益的好處。

One of the most beneficial effects of foraging in group for animals is enhancement of predation avoidance. Habitat type and group size are known to affect foraging and vigilance behaviors of the animals. We video-filmed and analyzed foraging, vigilance and moving behaviors of 127 focal Red Collared Doves (Streptopelia tranquebarica) in the western Taiwan to determine the effects of habitat types (open and obstructed) and group sizes (1 to 27 doves) on the behaviors. The results showed that the total foraging duration (sec) and number of pecking increased with the increase in group size at both habitats, while the total vigilance duration (sec), number of scanning bouts and scan duration were higher at the obstructed habitat than those at the open habitat. The group-size effect on vigilance was found only at the obstructed habitat but not at the open habitat. However, the low potential predation threats and possible use of peripheral vision to detect predators might dismiss the group-size effect. Also, the total moving duration (sec) decreased with the increase in group size, an indication of increasing foraging efficiency and anti-predatory benefits.