Male Hornbill Devotedly Delivers Food to His Mate Sealed in Nest
The female oriental-pied hornbill turns the tree hole into a predator-proof fortress. These birds are known for cavity-nesting behavior in tall trees and undisturbed habitats. The hole is built for protection from predators, and there are many of them. Once the female is inside, she does something very bizarre. She pulls out some of her flight feathers because she does not need them. Before going inside, the mates usually enlarge the hole slightly so that the female can fit through. During the nesting period, the female seals herself inside the cavity with a mixture of mud, droppings, and fruit pulp, leaving only a small slit through which the male passes food. It’s like a prison.

It takes a lot of time, and she stays sealed for a while, waiting for the male to bring food to her. She completely depends on him; if he never shows up, the female and her babies will simply starve. She will not leave the fort unless the chick is grown.
The male keeps coming in regularly for the next two months with food, which can be fruit, insects, or small animals. The more food he brings, the more she can produce eggs and keep them safe for another five to six weeks until they’re fully grown and fledged. When that time comes, they will break out of their prison. Once the chick is five weeks old, or if there are multiple chicks, they get out of there. Many observations on these hornbills prove how they time their nesting to perfection and stay consistent in parenting. This nurturing behavior is not unique to the oriental-pied hornbill; in fact, it is observed in about 60 different species of hornbills, highlighting the critical role of male hornbills in the survival and well-being of their offspring.
One of the fruits the male brings home is from a guava tree, the monsoon fruit that is beginning to ripen. The guava fruit is juicy and high-calorie, perfect for the female waiting. These birds are very sharing. Even when the female is outside her fortress, they share all sorts of food. Many times, one will bring food just to feed it to the other.
These hornbills have been observed plucking bats from mid-air when about 300,000 wrinkle-lipped bats are disgorged from their roosts in the dark cave. This behavior has only been observed in Borneo. Birds like Wallace’s hawk-eagle also join in, along with the cave racer snake. They all wait for the bats to come out, and since there are so many of them, it’s an easy catch, even for snakes. This bat-eating behavior was discovered recently, showing how they can adapt to their environment.
The use of abandoned clay jars
The really interesting thing is that they have been observed building nests not just in trees. In Sungai Panjang, Sabak Bernam, Selangor, Malaysia, their unique nesting behaviors have been documented. Oriental Pied Hornbills in the area of Sungai Panjang used abandoned clay jars. This research was put together in Malayan Nature Journal 2015, 67(1), 42-49. From 2009 to 2015, there were at least seven pairs that successfully bred and reared their young from an abandoned clay jar. Why are they doing that? the only valid answer is forest fragmentation, which has been shown to bring problems for many bird species when it comes to breeding. This makes them relocate, and it affects their outcome on breeding. Such a high significance is placed on the nest cavity that it is not possible to breed without it.
A group of 30 Oriental Pied Hornbills were often seen wandering in Sungai Panjang in 2008. Several surveys were made in the area, which located the breeding population. The population chose ground-nesting, utilizing abandoned clay jars as opposed to the normal tree-cavity nesting approach. This study examined the hornbill's activity of nesting and also brought out this unique adaptation to nesting exhibited by the species.
The location of the Sungai Panjang study site is in the Sabak Bernam District, Selangor State, 3o43.468'N 101o4.821'E.
The first nesting pair was discovered in January 2009, followed by four additional nests discovered in the same month. All the nests were monitored up to May 2011. In the research, binoculars, camera traps, and video recorders were used. The 2015 research paper on this behavior was authored by Ahmad Ismail, Faid Rahman, and Nurul Huda Abdul Jamil. The time recorded of entry for every pair, egg-laying and hatching, disturbances, breeding success, and related behaviors—highlighting the unconventional establishment and adaptive behaviors of the birds.
These jars are made from clay used by these Oriental Pied Hornbills in Sungai Panjang. The typical measurements for the jars are 58 cm in length, and 39 cm in width, with an opening diameter of 12 cm. They were once used widely among the villagers as a traditional means to store fermented food or water. Thus, the jars can easily be located within the populated area of Sungai Panjang. Before entering the nest, the male and female have been observed gathering earthen materials consisting of soil, small pebbles, and debris found around the research area. The materials were then put inside the jar layering its bottom. A similar description of the behavior was reported once before of the hornbill collecting soil from the ground which suggests that the behavior is uncommon. However, all the nesting pairs studied exhibited this unique behavior and this indicates the significant role of earthen materials in this unconventional nesting method.

The entrance-sealing technique of jars is similar to tree-cavity nesting. Only a small slit to the outside world and will require several numbers of patching to close the jars' opening. For each patch made, it would be completely dry after 2-3 hours and at least five days to complete the patching work. This leads to a narrow opening, a vertically slit of 11-12 cm in length and 3-4 cm in diameter. Through this slit, the female and its chicks breathe and retrieve food from its partner as well as for excretion purposes. The female puts her effort into keeping the jars' internal clean by removing all wastes outside and covering them with soil. This is yet another unique behavioral adaptation exhibited by the studied Oriental Pied Hornbill.
The breeding activity was completed by the pairs in 81 to 85 days in total. The pairs took, from first entry to sealing 5 to 7 days, sealing to the first egg laying 3 to 5 days, sealing to the last egg laying 11 to 13 days, sealing to the first hatching 29 to 32 days, sealing to the last hatching 36 to 40 days and sealing to exiting 70 to 78 days. This is relatively long compared to other reports that researched tree-cavity nesting. The clutch size is 1-2 eggs; however, two seems to be the most common. Only the male does the job of providing the female and the chicks with food during the whole nesting period. It will also reject the unconsumed food particles or food items that were not eaten by the female by throwing them far away from the nest with its beak. By the end of the study, at least 12 juveniles coming from seven pairs (47%) had been reared successfully throughout the breeding seasons. In contrast, the remaining eight pairs (53%) failed to complete their breeding activity. That was the breeding success of the Oriental Pied Hornbills recorded from 2009 to 2011.
It is suggested from studies that the breeding success rate for tree-cavity-nesting Oriental Pied Hornbills is between 64% and 80%. In one study in the northeast of India's Arunachal Pradesh State, the Oriental Pied Hornbill was reported to have an 80% successful fledging rate for tree cavity nests. This means 57 chicks successfully fledged out of 72 nests that were monitored by researchers over four years. It tells us that among the reasons affecting success, are habitat quality, food availability, predation, and most importantly, the nest itself.