Several species of hornbills are known to develop dorsal air sacs after hatching, which present as a pocket of air under their skin. These increase in size as the chicks grow, and gradually disappear as the chicks develop feathers. However, this feature is not well-described, nor do we know the extent it occurs in Bucerotids. Here, it is reported in a clutch of hand-reared Von der Decken’s hornbills (Tockus deckeni) (n = 5) at Jurong Bird Park, Singapore. Air sacs were not present at hatch, but developed within 24 h, increasing in size until about 10 days of age. They gradually recede from this age and are not always inflated, disappearing at about 16 days of age when the chick has considerable feather growth. The functions of this unique feature are largely unclear, but it is thought to be mostly related to thermoregulation. Further research is required to determine this, possibly using captive specimens from zoological institutions as it is more difficult to collect data from wild birds.

中文翻译：

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手饲养的冯德戴肯犀鸟 (Tockus Decken) 背气囊发育的简要报告

已知有几种犀鸟在孵化后会形成背部气囊，在它们的皮肤下表现为一个空气袋。这些随着雏鸡的成长而增大，随着雏鸡长出羽毛而逐渐消失。然而，这个特征没有得到很好的描述，我们也不知道它在 Bucerotids 中出现的程度。在这里，在新加坡裕廊飞禽公园的一群手工饲养的冯德戴肯犀鸟 (Tockus deckeni) (n = 5) 中报道了这种情况。孵化时不存在气囊，但在 24 小时内发育，直到大约 10 日龄时体积增大。从这个年龄开始，它们逐渐消退，并不总是膨胀，在大约 16 日龄时消失，此时小鸡的羽毛长得可观。这种独特功能的功能在很大程度上尚不清楚，但被认为主要与体温调节有关。