Biology and Ecology of Two Endangered Species Rufous-necked and Plain-pouched Hornbills in Huai Kha Khaeng Wildlife Sanctuary

INTRODUCTION

Hornbills are among the largest and most conspicuous birds in old world tropical forests. They are known to be among the most easily surveyed of forest organisms, allowing both visible and audible means of identification (Kemp & Kemp 1974; Poonswad et al. 1987, Johns 1987, 1988).

The remarkable nesting habit is that the female seals herself in a large cavity of a living tree leaving only a narrow opening for her mate to pass food to her and later chicks. They are omnivorous feeding on a great variety of fruits and animals. Thus, they are important for seed dissemination and keep balance of some animal groups in the forest (Poonswad et al. 1987, Kemp 1995).

Among 31 species of hornbills found in tropical and subtropical Asia, there are 13 species occur in Thailand (Kemp 1993, Poonswad 1993b). Other than morphology and distribution described from India. Myanmar (Ali & Ripley 1987, Smythies 1986) and Thailand (Lekagul & Round 1991), Rufous-necked (Aceros nipalensis) and Plain-pouched Hornbills (Aceros subruficollis) are ranked as little known species particularly, breeding biology (Kemp 1993). Rufous-necked Hornbill is also believed to be extirpated from Nepal since 1846 (Shrestha 1993).

This study reports 1) habitat preference, 2) nest and nest site or nest habitat characteristics 3) breeding biology 4) flocking and roosting.

STUDY AREA AND METHODS

Huai Kha Khaeng Wildlife Sanctuary is situated in western Thailand and covering 2,809 km² (Fig. 1). The area experiences south-west monsoons and the mean annual rainfall at Khao Nang Rum Wildlife Research Station in l993-96 was 1,557 mm. Most precipitations fallen during May to October with an annual mean of 1,165 mm falling during this period (Fig. 2). The driest months were December and January when the average rainfall of the month was only 6.2 mm. (Fig. 2).

Figure 1. Map of Huai Kha Khaeng Wildlife Sanctuary.

Figure 2. Monthly data of precipitation during January 1993 - December 1995 measured at KhaoNang Rum wildlife Research Station, Huak Kha Khaeng Wildlife Sanctuary.

Data records

Distribution

The study of distribution was performed from 1994 to 1996 by sighting of hornbills while hiking along existing trails as well as by hearing of calls. Then mapping of sighted and heard hornbills was done.

Biology and ecology

During 1990-1996, nest trees were located either by following lone males from feeding sites or by inspecting large trees with visible cavities. Active nests could be confirmed by the deposits of droppings, accumulations of nest debris, and seed regurgitates (Poonswad et al. 1987). Once discovered, each nest tree was mapped and was studied as in Poonswad (1995). The methods to study Rufous-necked and Plain-pouched Hornbill's nest sites were modified from Liewviriyakit (1989).

Observation from the female imprisonment by checking the nest entrance sealing and chick fledging by detection of nest plaster debris were carried out from December 1994 to February 1996. When possible nests were also visited at 1-7 days interval from mid March to the last week of June. Observations on flocking and roosting followed the method of Poonswad (1993a).

RESULTS

Distribution of hornbills

Rufous - necked Hornbills were found distributed in dry evergreen, moist evergreen and hill evergreen forests whereas Plain - pouched Hornbills were found in mixed deciduous and dry evergreen forests along the stream.

Biology and ecology

Rufous - necked Hornbill : Twelve nests of Rufous-necked Hornbills were found in hill evergreen forest ranging from 1,018 to 1,300 m a.s.l. (mean = 1144.7 ± s.d. 98.7 m a.s.l.). Characteristics of nests and nest trees are presented in Table 1.

Table 1. Characteristics of nests and nest trees of the Rufous-necked Hornbills in Haui Kha Khaeng

Five of 0.8 hectare plots were set at 5 nest sites, 466 trees were recorded. There were at least 61 genera identified but 78 trees were unidentified. The forest structure at nest sites was divided into three layers, i.e. top (or emergent), middle (or main) and low layers, excluding the forest floor (Table. 2) .

Table 2. Summary of characteristics of some nest sites of the Rufous - necked Hornbill studied in a 20 x 80m sample plot at each site in Huai Kha Khaeng. IVI=Important Value Index.

Total 12 nests were distributed in all three forest layers; 1 nests (8.3%) was in the top, 7 nests (66.7%) were in the middle and 3 nests (25%) were in the low layers. Most of Rufous-necked Hornbills nested in cavities located in the trunk of living trees (91.6%). Only one nest was found in a cavity of a dead tree (8.3%).

The breeding cycle defined as the period from the female imprisonment to the last chick fledging Rufous-necked Hornill female's imprisonment started from 10 January to 17 February (median = 22 January, n = 11 pairs). Female emergence and young fledging varied from 9 May to 21 June. The average breeding period was 125.3 ± 7.1 days (n=6). The emergence of female from the nest occurred before or on the same day as chick fledging. The female emergence dates varied from 9 May to 21 June (median = 25 May, n = 7). Each breeding pair raised 1-2 chicks. The mean chicks per nest was 1.3 ± s.d. 0.5 (n=9). Before fledging period, one female and three chicks of two nests were eaten by Yellow-throated Martens Martes flavigula and a female of one nest was eaten by a Binturong Arctictis binturong. Then, breeding success was 78%. Rufous-necked Hornbill flocked in a small number and had never been observed in mixed flock with other species. The maximum number of individuals in a flock was 11 observed in 1996. But in 1993, maximum number was 18.

Plain-pouched Hornbill: Nine nests were found distributed in mixed deciduous forest. Characteristics of nests and nest habitat were summarized in Tables 3 and 4. Seven nests out of 9 nests were in former woodpecker's holes judging from the shape of nest entrances which were round or nearly round. All 9 nest trees were alive, 8 nests were situated in the trunk of the trees one was in a branch. In the study area of 2 x 5 km², there were two characteristic types of the mixed deciduous forest one of which is influenced by seasonal flooding (Table 4).

Table 3. Characteristics of nest trees and nests of Plain-pouched Hornbill in Huai Kha Khaeng.

Table 4. Summary of characteristics of nest habitat of the Plain-pouched Hronmill in 15 plots (size of plot = 24 x 100m) near stream and 25 plots away from stream.

Nests were monitored for the female imprisonment and chick fledging only. The peak of imprisonment fell into two periods, i.e. the last week of January and the first week of February. Chick fledging ranged from 11 May to 24 May (n=8 pairs). The entire breeding cycle of the Plain-pouched was shorter than the Rufous-necked Hornbill, i.e. mean = 113.6 ± 12.1 days (n = 5 pairs). From 11 observed breeding pairs, 8 pairs fledged (72.7%) with unknown number of chick per nest. A female of one nest was found dead of an unknown cause and two females emerged before 20 April without any chick.

Plain-pouched Hornbill was often found in mixed flock with Wreathed Hornbills and gathered in smaller flock than the Wreathed Hornbill. Maximum number of individuals per flock was not more than 34 in 1996. In contrast, the Wreathed Hornbill flock size reached 633 in 1996 observed at the same roost.

DISCUSSIONS

Nests and nest site

We agree with Kemp (1976) and Poonswad (1993a) that there is no specific preference on tree species for nesting. Hornbills use tree species that are large and abundant. When comparing these two studied species with the Wreathed Hornbill, it was obviously confirmed that these three species of the same genus nest in different habitats, i.e. Rufous-necked in hill evergreen forest, Wreathed Hornbill in moist evergreen forest (Poonswad 1993a) and Plain-pouched Hornbill in mixed deciduous forest. Nest characteristics of these species differed in details.

Breeding biology

All breeding females of the studied species began to nest in dry season starting in January - February and leaved the nest during May - June was similar to the breeding cycle of Wreathed Hornbill in Khao Yai National Park (Poonswad et al. 1987) and was similar to the breeding season of this species in India (Ali & Ripley 1987). Not only Rufous-necked Hornbill left the nest during this period but also the sympatric species, Great and Brown Hornbills did in this study area Plain-pouched Hornbill in this study, on the other hand, had similar breeding season as in Myanmar (Smythies 1986).

The difference in length of the breeding cycle may be affected by a size of birds and feeding strategy (Poonswad 1993a). The sizes of these three species Rufous-necked, Wreathed and Plain-pouched Hornbills are 117 cm, 100 cm and 90 cm respectively (Lekagul and Round 1991). Plain-pouched Hornbill is the smallest among these species Unfortunately, feeding strategy for the studied species is not determined.

Flocking and roosting

A flock size of the two studied species when compare with the Wreathed Hornbill studied in Khao Yai National Park and in this study area was obviously different. Both studied species formed small flock consisting of not more than 40 individuals, whereas the Wreathed Hornbill may flock up to 1,000 individual at the roost (Poonswad et al. 1987).

CONCLUSION

The study confirmed the habitat preference of Rufous-necked to hill evergreen forest and Plain-pouched to mixed deciduous forest.

Other accounts are as follows:

Rufous-necked Hornbill: Nests were located at averaged altitude of 1,144 m a.s.l. in hill evergreen forest. The favored nest tree was the tree of genus Syzygium which found to be the common tree. Nest height of this species was similar to the Plain-pouched Hornbill.

Breeding season started in late January and finished in late May to early June. The breeding cycle took about 125 days, Natural predators were marten and binturong. In non-breeding season, the species gathered in a small flock of up to 18 individuals.

Plain-pouched Hornbill: Nests were located at averaged altitude of 231 m a.s.l. in mixed deciduous forest. The favored tree for nesting was tree of genus Tretrameles which is found along the stream. Majority of the nests were in former holes of woodpeckers. The average nest height above the ground was 16.6 m.

Breeding season also started in January and lasted in mid May. The breeding cycle took about 113 days which was shorter than the former species.

In non-breeding season, the species gathered in a small flock not more than 40 individuals.

REFERENCES

ACKNOWLEDGMENTS

Sincerely appreciation must be extended to Royal Forest Department which kindly permitted research of hornbills to be undertaken in Huai Kha Khaeng Wildlife Sanctuary under its jurisdiction.

Many thanks go to Dr. Satoshi Yamagish, beside serving as the reference of this project he also kindly gives valuable comments and endless encouragement.

Our special thanks go to Atsuo Tsuji who take trouble and time to translate from English to Japanese language all reports through out the project.

We also extend our thanks to chief of Huai Kha Khaeng Wildlife Sanctuary and all superintendents of Khao Nang Rum Wildlife Research Station for their excellent cooperation throughout this study.

Sincere thanks go to Sopha Sungruksa, Siriwan Nakkuntod for their assistance in preparing and typing all reports.

This research was supported by Pro Natura Foundation - Japan.

Summary

The study shows that Rufous-necked Hornbill (RNH) preferred hill evergreen forest and Plain-pouched Hornbill (PPH) preferred mixed deciduous forest. The nests of RNH were located at 1,144 m a.s.l. Favorite nest tree was Syzygium, was 37.8 ± 7.8 m high and 94.9 ± 16.8 cm dbh. The nest was 15.8 + 7.3 m above the ground which was in the middle layer of the forest strata. Nests of PPH were located at 231 m.a.s.l on average. Favorite nest tree was Tetrameles with height at 44 ± 8.5 m and dbh at 205 ± 97.6 cm. The nest above the ground was 16.6 ± 4 m and was within the middle layer of the forest strata. Majority of the nests were in former woodpecker holes.

Breeding onset of both RNH and PPH was triggered by the drought. RNH started to nest in late January and finish in late May to early June. Breeding cycle took 125 days on average. PPH started to nest in late January to early February and lasted until mild May. Breeding cycle took 113 days on average.

Natural predators of RNH were Yellow-throated Marten and binturong. Natural predator of PPH was suspected to be marten.

In non-breeding season, RNH gathered in smaller flocks of up to 18 individuals, while PPH gathered up to 40 individuals.

要旨

タイ国におけるサイチョウ危急種2種の生態研究

この研究で、Rufous-necked Hornbill（以下RNH）［ナナミゾサイチョウ、Aceros nipalensis] が丘陵常緑林を好み、Plain-pouched Hornbill (以下ＰＰＨ）［Aceros subruficollis は落葉混交林を好むことが示された。

RNHの巣は、平均海抜1,144mに位置し、もっとも好まれた樹種は、Syzygium [フトモモ属］で、平均樹高37.8±7.8m、胸高直径94.9±16.8cmであった。巣の位置は地上から平均15.8±7.3mの高さにあり、森林層の中層に位置していた。

PPHの巣は、平均海抜231mにあり、樹種はTetrameles［テトラメレス科]で平均樹高44±8.5m,胸高直径205±97.6cmであった。巣の地上高は16.6±4mで同じく森林層の中層にあった。巣の多くはキツツキの古い巣穴を利用していた。

RNH、PPHともに、繁殖行動の開始は、干ばつが引き金になっていた。RNHは１月下旬に巣入りし、5月下旬から6月上旬に巣立ちした。繁殖期間の平均は125日だった。

PPHは、1月下旬から2月上旬に巣入りし、5月中旬に巣立ちした。繁殖期間の平均は113日であった。

RNHの天敵はYellow-throated Marten [テン］とBintorong [熊猫］であった。PPHの天敵はやはりMartenと思われる。

非繁殖期には、RNHは最大18個体の比較的小さな群をつくり、PPHは最大40個体の群れをつくっていた。