傍晚時分，數百隻的雌性臺灣小蹄鼻蝠(Rhinolophus monoceros)在隧道開口處盤旋，等待著飛離的契機。此時，在近1km深處的隧道底，有一群暫時被留下的新生小蹄鼻蝠寶寶，顯然這隧道是臺灣小蹄鼻蝠用來生殖育幼的棲所。這些正準備離開隧道棲所的蝙蝠媽媽們，透過數次來回逼近隧道口的方式，藉由評估光線亮度(light sampling)以決定外出覓食的時機。由於在許多蝙蝠棲息的洞穴或隧道外，常有猛禽出沒，準備隨機捕抓警覺度不高的蝙蝠。因此，蝙蝠如果在外界仍然太亮時飛離隧道，很容易受到依靠視覺狩獵的猛禽攻擊。為了將被捕食的機率降到最小，蝙蝠常大量、緊密成群地飛出洞穴，而且每隻個體都試圖擠進飛行團隊中間，避免身處外圍而被猛禽捕獲。如飛離隧道時天色未全暗，蝙蝠也會小心地不要暴露在空曠處，以降低受到來自猛禽的傷害。因此，常可見蝙蝠傍晚開始覓食時，總是貼近地面或圍繞著樹叢飛行。如此一來，即便是最銳利的猛禽眼睛，都難以發現牠們的蹤跡。
相較於猛禽，蝙蝠的飛行速度與視覺能力都屈居於劣勢，為了躲避來自鷹、隼或其他鳥類的攻擊，也是促使蝙蝠成為夜行動物的主因之一。然而，蝙蝠在夜間活動能具有優勢，這就得感謝牠們所擁有的回聲定位(echolocation)能力了。

Hund reds of fema le little horsesho e batsRhinolophus monoceros congregate at the tunnelentrance just before the evening emergence, flyingback and forth in a left hand loop. Their maternityroost, now with the newborn young left behind, islocated almost a kilometer away, at the far end of thetunnel. By approaching the entrance from the insideseveral times, the bats do what is called “lightsampling”, checking that the ambient light level isappropriate for safe departure from the tunnel andtowards the hunting grounds. Particularly at roostswith many bats, birds of prey often wait outside,ready to catch any careless bat. Therefore, leavingthe safety of the tunnel while the light is still brightoutside is extremely dangerous, since it would makethe bat vulnerable to attacks from birds of prey,which hunt by vision. To minimize the risk evenfurther, the bats emerge in large coherent groups,each individual trying to stay in the middle of theflock, so that other individuals are caught first. Oncethe bats are outside the tunnel, they are careful notto expose themselves in the open air before it is fully dark, while they may still be vulnerable to attacksfrom birds. They always start to hunt in the shadenear the ground or among the leaves and branches oftrees, where they would be hard to spot and followeven for the sharpest eyes.
Compared to birds of prey, bats are slowflying and have poor vision, and so are always at adisadvantage, as long as the birds can see properly.The necessary avoidance of hawks, falcons and otherbirds is in fact the principal reason why bats nearlyalways are strictly nocturnal. At night, the bats havethe advantage, thanks to their ability of echolocation.