Hajanirina Rakotomanana*, Masahiko Nakamura**1) the Hook-Billed

山階鳥研報 (J. Yamashina Inst. Ornithol.), 33: 25-35, 2001

Breeding Ecology of the Endemic Hook-billed Vanga, Vanga curvirostris, in Madagascar

Hajanirina Rakotomanana*, Masahiko Nakamura**1) and Satoshi Yamagishi***

Abstract. The breeding ecology of the Hook-billed Vanga Vanga curvirostris, which is endemic to Madagascar, was studied on the Masoala Peninsula, northeast Madagascar in October 1999, and in the Ankarafantsika Strict Nature Reserve from October 2000 to January 2001. Five nests discovered during our study were all located 3-10m above the ground in the forks of trees ranging from 390-1260mm in diameter at breast height. Two adults (perhaps a heterosexual pair) participated equally in nest construction, incubation, and care of the young at each nest, and no helpers were observed. Incubation lasted between 22 and 24 days. The nestling period was 20 to 22 days, and the parents delivered invertebrates and small vertebrates, including mainly geckos and chameleons, to nestlings. External morphometric measurements of specimens suggest that the Hook-billed Vanga lacks sexual dimorphism in body size. Less-marked sexual dimorphism, biparental care, and similar sex roles show the Hook-billed Vanga to have a monogamous mating system. Key words: biparental care, breeding ecology, Hook-billed Vanga, Mada- gascar, monogamy. キーワード:両親による子の世話,繁殖生態,カギハシオオハシモズ,マダガスカル,一夫一妻.

Introduction The Hook-billed Vanga Vanga curvirostris belongs to the family Vangidae, which is endemic to Madagascar. It is distributed along the coast, in forested and wooded areas around villages, from sea level to 1,800m (Langrand 1990). Based on its body color and bill shape, Milon et al. (1973) recognized three subspecies: Vanga c. curvirostris (bill with a slightly curved culmen) inhabits the eastern forest, mangroves on the northwestern coast, and the wooded area in western Madagascar; V. c. cetera (bill with a straight culmen) is found in subarid thorn scrub, in southern Madagascar; V. c. griseipectus (color is darker than the two others) populates the southeastern coast, but it is rare. Despite the species' widespread distribution in Madagascar, there have been only a few studies of its breeding ecology, owing to inherent difficulty in observing birds in the field, and these have yielded fragmentary data (e. g., Appert 1970; Milon et al. 1973, Langrand 1990, Yamagishi et al. 1997, Morris & Hawkins 1998). In this paper, we report the first systematic study of the breeding ecology of the Hook-billed Vanga. Received 20 April 2001, Revised 15 June 2001, Accepted 22 June 2001. * Cite 67 ha Sud Logt 315 , Antananarivo (101), Madagascar. ** Laboratory of Animal Ecology , Joetsu University of Education, 1 Yamayashiki-machi, Joetsu-shi, Niigata 943-8512, Japan. *** Department of Zoology , Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan. 1) Corresponding author

25 26 H. Rakotomanana, M. Nakamura and S. Yamagishi

Study Areas

The study was conducted in two different areas. The first study area was the

Ambanizana rainforest, on the Masoala Peninsula, northeastern Madagascar (15°37'S, 49°58'E), from sea level to an altitude of 1,200m. The rainforest is composed of primary forest and secondary growth of high floristic diversity; the canopy is ca. 30m high, with some emergent trees (Jenkins 1987). We found one nest, and observed the incubation behavior in October 1999. September to November are the driest months; monsoon rains and cyclones usually occur between December and April. The average annual precipitation recorded at Andranobe Field Station, ca. 8km south of the study site, was 6,046mm from 1991-1996 (Thorstrom et al. 1997). The second study area was the Ampijoroa Forest Station (in the Arboretum, Jardin A and near National Road 4 [NR4] ), located within the Ankarafantsika dry forest reserve (16°15'S, 46°48'E), about 110km southeast of Mahajanga, at an altitude of 200m above sea level. The wooded area around the Station contained mainly Hura crepitens (Euphorbiaceae), Eucalyptus spp. (Myrtaceae), and Tamarindus indica (Fabaceae), while the deciduous primary forest consisted of Fabaceae, Euphorbiaceae, Burseraceae, Sterculiaceae, and Hypericaceae. A detailed description of the vegetation can be found in Razafy (1987). Two main seasons occur in the area: a rainy season (November-April) and a dry season (May-October). The average annual precipitation is about 1,250mm, and the mean annual temperature is 24.5℃ (Conservation International 1999). We found four nests in the reserve, and studied breeding behavior from October 2000 to January 2001.

Material and Methods Both sexes are similar in appearance in Hook-billed Vangas (Langrand 1990). To examine the sexual dimorphism in body size, museum specimens from Cornell University Museum, USA, and the Botanical and Zoological Park of Tsimbazaza (PBZT), Madagas- car, and a dead specimen collected near Ampijoroa Village were measured. The average external morphological measurements (ｱSD) of the two sexes were as follows: bill length (exposed culmen): 29.0ｱ1.3mm, (natural) wing length: 104.8ｱ8.4mm, tail length: 105.6ｱ12.Omm, tarsus length: 30.1ｱ3.9mm for six males, and bill length: 28.4±1.5 mm, wing length: 107.9ｱ5.3mm, tail length: 97.2±3.3mm, tarsus length: 32.9±3.4mm for three females. There were no significant differences between the measurements of the two sexes (Mann-Whitney U-test, P>0.05 for each measurement). This result suggests that the Hook-billed Vanga lacks sexual dimorphism in body size. We were unable to determine the sex in the field and to capture the birds for individual marking. However, we could discriminate between the birds attending a nest using variation in the color of the tail tip, shape of the bill tip, and length of the rictal bristles. To search for Hook-billed Vanga nests, which are usually placed in the fork of a tree at varying heights (Langrand 1990, Morris & Hawkins 1998), we walked along trails or small paths in forested or wooded areas. Once a nest was found, we started observations.

Both direct observations (using a 20 × spotting telescope) and indirect observations Breeding Ecology of Hook-billed Vanga 27

(recording by a video camera; Sony Hi8, CCD-TRV66) were made to study the breeding ecology of the Hook-billed Vanga. Daily observations lasted from 0530 to 1100 or from 1200 to 1800, and totaled 153 h by telescope and 52 h by video camera. Data from the direct and indirect observations were combined. We named five nests as Nest A (in Ambanizana) and B-E (at the Ampijoroa Forest Station). Two nests in building stage were investigated for 18 h at Nest B on 22-25 October 2000, and for 11 h at Nest D on 18-19 November 2000. Incubation behavior was studied at other nests for 23 h at Nest A on 28-30 October 1999, and for 53 h at Nest C from 23 November-11 December 2000. Nest A was found in the incubation period. It was only observed on three consecutive days, so we could not take any nesting data from this nest. The nestling stage was studied at Nest C for 95 h and at Nest E for 5 h. To examine the relative contributions of the birds to reproductive effort, we studied nest building, incubation, brooding, feeding frequency (times/h/brood), and prey items delivered to nestlings. Birds were referred to by a number followed by a lowercase letter indicating the nest, e.g., Bird 1a and Bird 2a for Nest A. We calculated the percentage of time that individuals spent nest building, incubating, and brooding. Incubation and brooding sessions were defined as starting when a focal individual began either incubating eggs or brooding nestlings, respectively, and as ending when the individual left the nest. We evaluated the size of prey relative to the bird's bill size. Nest location, nest tree species when possible and nest tree characteristics (height, diameter at breast height [DBH] ) were recorded. Nest materials and size were examined and described for only accessible nests (Nests B and D). The number of eggs and their color at Nest were checked by climbing the nest tree.

Results

Nest profile The location and nesting tree characteristics of the five nests examined during our investigation are summarized in Table 1. Nests C-E were located near the NR4 (Table 1). Nest D was located about 1.3 km away from Nest C, which was located about 1.0 km away from Nest E. The exterior nest diameter was 135×220(Nest B) and 120x200mm (Nest D), The interior diameters of the two nests were 105x110 and 85×87 mm, respectively. The exterior of both nests was 100 mm deep, and the interior at the center of Nests B and D was 50 and 60 mm, respectively. Nest B was constructed mainly from green roots of Goussonia sp. (Orchidaceae), reinforced internally with adventitious roots of Ficus sp. trees (Moraceae) and twigs of the parasitic plant Cassyta filiformis (Lauraceae), and covered with caterpillar or spider cocoon husks and some mosses. Nest D was made mainly of twigs of Albizzia sp. (Fabaceae), internally reinforced with some adventitious roots of Ficus sp. trees (Morac- eae) and green roots of Goussonia sp. (Orchidaceae), and covered with spider webs. 28 H. Rakotomanana, M. Nakamura and S. Yamagishi

Table 1. Location, nesting tree, height of nesting tree (m above ground), nesting height and diameter at breast height (DBH) for five nests.

* NR4 means National Road 4 .

Nest building stage When Nests B and D were found, nest constructionhad alreadystarted, so we could not determine the exact duration of nest building. During our observations,two birds contributedto nest buildingat each nest. At Nest B, Bird 1b brought 0.96items of nest material/h and Bird 2b brought 1.36items/h;Birds 1d and 2d brought 2.56 and 3.92 items/h,respectively, at Nest D. The totaltime spent working on nest constructionat Nest B was 7.5 min for Bird 1b(0.7%of the time)and 21.9 min for Bird 2b(2.1%of the time). The time spent totaled19.7 min for Bird 1d(3.0%of the time)and 29.0 min for Bird 2d(4.5%of the time)at Nest D. The average time spent building per visit was 0.3 min for Bird 1b (n=23, range: 0.1- 3.0 min) and 0.7 min for Bird 2b (n = 30, range: 0.2-2.0 min) at Nest B. The difference in the time spent for building differed significantly between these two birds (Mann- Whitney U-test, U=161.0, P = 0.001). It was 0.9 min for Bird 1d (n = 21, range: 0.1-3.0 min), and 0.8 min for Bird 2d at Nest D, (n = 35, range: 0.1-2.0 min); the difference was not significant (Mann-Whitney U-test, U= 366.0, P= 0.97). Bird 1d was closely followed by Bird 2d at Nest D. Bird 1d was taking small lizards (Phelsuma madagascariensis and Homopholis sakalava) in its bill. We observed that Bird id gave the food items to Bird 2d with infantile calls and the posture accompanied by wing fluttering as begging posture of young birds. We recognized a unique call in adult Hook-billed Vangas from the nest building to the post fledgling period. It consisted of a single monotonous note, sounding like "peew", lasting for two seconds, and repeated at short regular intervals. Adults were difficult to locate, because they uttered calls while concealed in foliage high at the treetops. This call seemed to be associated with contact between a pair or territorial communication, because two birds often responded to each other by this call when one bird was out of visual contact. Breeding Ecology of Hook-billed Vanga 29

Incubation behavior Birds 1aand 2a incubated a clutchof threeeggs at Nest A(Fig.1). The eggs were elliptical,smooth, white,and denselycovered with small wine-red spots.These two birds incubated the eggs in 86.9% of the time(data were pooled for three days). The total incubationtime observed in Birds 1a and 2a was 645 and 554 min, respectively.The average incubationsession was 64.5 min for Bird 1a(n=10, range:24-110 min), and 42.6 min for Bird 2a(n=13, range:2-85 min);the differencewas not significant(Mann- Whitney U-test,U=40.0, P=0.12). Similarly,two birdscontributed to incubationat Nest C(Fig.1). Birds 1cand 2c incubatedthe eggs in 87.5% of the time(data were pooled for 10 days). The totalincubation time observed in Birds 1cand 2c was 1361 and 1420 min, respectively.The average incubation sessioninvolving Bird 1c was 30.9 min(n=44, range:2-82 min)and thatby Bird 2c was 27.8 min(n=51,range:3-101 min). There was no significantdifference in the duration of the incubation sessionsof these two birds (Mann-Whitney U-test,U=1055.5, P=0.62). We did not observe any contributionsby the thirdbird during thisperiod. Full-time incubation(incubation occurred more than 80% of the time)was seen on 23 November 2000 at Nest C. Based on the firstprey delivery to the nest and eggshell removal from the nest, we assumed that the clutch hatched at dawn(ca.0500)on 14 December 2000. Video records on 20 November 2000 showed part-time incubation (incubation occurred less than 80% of time). Therefore, full-timeincubation began on 21-23 November 2000, implying that the incubation period lasted from 22-24 days.

Date Fig. 1. Incubation time budgets of Hook-billed Vangas at two nests. Open bar: Birds 1a or 1c; solid bar: Birds 2a or 2c. The observation period (hours) for each day is given in parentheses above the bars. 30 H. Rakotomanana, M. Nakamura and S. Yamagishi

We observed a changeover in incubation 68 times at the two nests. As soon as the incubating bird left the nest, the other came and sat on the nest. When the bird returned , the incubating bird flew off the nest immediately. No vocalization to alert the incubating individual was heard. Occasionally, a non-incubating bird delivered prey to an incubating individual , especially near the beginning of this period. Bird 1a delivered food to Bird 2a three times at Nest A and Bird 1c delivered prey to Bird 2c five times at Nest C. When this happened , the incubating individual shook its wings in the nest.

Brooding Two adultsshared a duty involvedin broodingat Nest C containingfive nestlings (Fig.2).The totalnest attendance for Birds 1cand 2c was 434.5(7.6% of thetime)and 950.9min(16.7% of the time),respectively. Nest E had at leasttwo nestlings,and two adultstook partin broodingand feeding,but our datawere incompletedue to difficulties in observingthe nest. Brooding activity decreased with growth of the nestlings (Fig. 2). A brooding session averaged 7.2 min (range: 0.2-22.0 min, n= 49) for Bird 1c, and 8.1 min (range: 0.2-34.0 min, n=106) for Bird 2c, with no significant difference (Mann-Whitney U-test, U= 2449.5, P=0.57). During a brooding session, the brooding individual often shook its body slightly, changed its orientation, and preened itself. The brooding individual poked into the interior of the nest with its beak, picked up unidentified items (perhaps feces, 0.36 items/ h for Bird 1c and 0.64 items/h for Bird 2c), and sometimes ate them .

Nestling age (days old) Fig. 2. Brooding time budgets of Hook-billed Vangas at Nest C. Open bar: Bird 1c; solid bar: Bird 2c. Nestling age is given in days after hatching (day 0 is the hatching date). The observation period (hours) for each day of nestling age is in parentheses above the bars. Breeding Ecology of Hook-billed Vanga 31

Feeding nestlings Two birds (Birds 1c and 2c) delivered food to nestlings at Nest C. No helpers were observed in this nest (Fig. 3). The feeding frequency increased until 8 days after hatching, and subsequently decreased (Fig. 3). Feeding frequency averaged 0.53 times (range, 0.12-0.92; n=16 days) for Bird 1c and 0.55 times (range 0.20-1.04; n=16 days) for Bird 2c. The difference between both individuals was not significant (Mann-Whitney U-test, z =0 .23, P=0.82). Of the four nests studied in Ampijoroa, two could not be investigated until the nestling period; one (Nest B) suffered predation by an unknown animal at the incubation stage, and the other (Nest D) was abandoned at the nest building stage (it was probably disturbed by village people). In Nest C, one of five nestlings fledged at 0725, 21 days after hatching (29 December) and four fledged between 0815 and 1115, 22 days after hatching. It showed that the nestling period was 21 to 22 days. In Nest E, the eggs hatched on 28 December 2000, and two nestlings fledged on 18 January 2001. In this case, the nestling period was 20 days. We have no exact data on the post-fledgling period. At 1630 on 5 January 2001, five young (28 days old) from Nest C were last observed roosting 6 m above the ground, in two small trees, about 50 m northeast of the nest tree. They uttered calls constantly for about 15 min, and may have been waiting for the adults to deliver prey. The call was a typical fledgling call, "peee-peee-peee", like a mewing call.

Food habits During the nestling period, the Hook-billed Vangas delivered 506 items. Of these, 8.9% were invertebrates, 65.6% were vertebrates, and 25.5% were unidentified (Table 2).

Fig. 3. Feeding frequency of Hook-billed Vangas in relation to age of the nestling at Nest C. Open bar: Bird 1c; solid bar: Bird 2c. Nestling age is days after hatching (day 0 is the hatching date). The observation period (hours) are given in parentheses above the bars. 32 H. Rakotomanana, M. Nakamura and S. Yamagishi

Table 2. Prey delivered by the Hook-billed Vanga during the nestling period at Nest C. Prey items were pieces of body (lizard's leg, tail, head, etc.) or the whole body.

The prey size ranged from 4 mm (e.g., a fly) to 10 cm (e.g., a lizard). Some were eaten by the parents when they were too big for nestlings (8 observations). Bird 1c passed food (fresh meat and unidentified prey) to Bird 2c twice and the latter put the prey in the mouth of a chick. Pieces of fresh meat from different small vertebrates, including the Madagascar Day Gecko Phelsuma madagascariensis and chameleons (Furcifer oustaleti and F. rhinoceratus) were the prey delivered most frequently, representing 90.4% of 157 identified vertebrates. Most prey were seized on branches, from treetop level to just above the ground. Prey were killed by squeezing them with the bill (in the case of insects) or by pecking and carving them with the bill on a branch near the nesting site (small vertebrates). Then, the adults took the body pieces to nestlings. After swallowing, the parent always cleaned its bill on a small branch, especially when the prey was sticky or juicy. Thirteen days after hatching, the parents fed their young pieces of a chick of other bird species (with downy white feathers) and the young swallowed them voraciously.

Interactions with other species Individuals of all five pairs that we studied were sensitive to threats near their nests; when the wind blew or a car passed by (for nesting sites near the road), or when the call of other species (White-headed Vanga Leptopterus viridis, and Broad-billed Roller Eurys- Breeding Ecology of Hook-billed Vanga 33 tomus glaucurus) became louder, the parent on the nest remained motionless and silent, and turned its head up. When a big bird (Crested Coua Coua cristata or Madagascar Buzzard Buteo brachypterus) became a real threat near the nest (e.g., soaring above the nest), the nest owner left the nest and perched on the nearest branch. The pair of Nest D chased other species that approached the nest (e.g., Madagascar Magpie-Robin Copsychus albospecularis, Broad-billed Roller, Gray-headed Lovebird Agapornis cana, Madagascar Bulbul Hypsipetes madagascariensis, and Brown lemur Eulemur fulvus) making two or three bill claps. On the other hand, they were driven away by the Madagascar Bulbul and the Madagascar Paradise Flycatcher, Terpsiphone mutata, which might have had nests near Nest D. When other species approached the nest, the call including two or three bill claps followed by "kraa-kraa-kraa pew-pew-pew" used as an alarm call.

Discussion Some traits that characterize monogamous breeding systems include less marked sexual dimorphism (Andersson 1994, Ligon 1999), biparental care, and similar sex roles (Ligon 1999). Morphological measurements suggest that the Hook-billed Vanga lacks sexual dimorphism in body size. Two adults (perhaps a heterosexual pair) participated equally in nest construction, incubation (Fig. 1), and care of young (Figs. 2 and 3). The parents were not aided by any helpers in any of these nesting activities, unlike in some vangid species, such as the Rufous Vanga Schetba rufa (Yamagishi et al. 1995), the Chabert's Vanga Leptopterus chabert (Appert 1970), and the White-headed Vanga (Naka- mura et al. 2001). Thus, we conclude that the mating system of the Hook-billed Vanga is best described as socially monogamous. This description is supported by observations made by Milon et al. (1973) and Langrand (1990), who usually found this bird alone or in pairs both in the breeding and non-breeding seasons. We observed courtship feeding during the beginning of the incubation period at Nests A and B, and during the nest-building period at Nest D. In all of these episodes, an individual who gave the food closely followed its partner. Since males in many passerines guard their mate before incubation (Birkhead & Moller 1992), the individual that gave the food might have been the male. Courtship feeding is considered to be one aspect of an exclusive mating relationship between a male and a female, and probably contributes to strengthening of the pair bond (Lack 1940, Smith 1980). We confirmed that the Hook-billed Vanga is a "predatory passerine", as reported by Morris & Hawkins (1998), for two reasons: its hunting method and its food habits. The Hook-billed Vanga hunts for its prey from treetop to just above the ground, in a manner similar to that of Sparrow Hawks (Cramp & Simmons 1980), i.e., it flies little, usually spending long intervals motionless on a perch, watching for prey, and then surprises it (Yamagishi & Eguchi 1996). Our diet data confirm that the Hook-billed Vanga has carnivorous tendencies, as mentioned by Milon et al. (1973) and Langrand (1990). During the late nestling period, nestlings regurgitated moths fed by the parent and put them aside, while they swallowed vertebrates whole or in pieces. This suggests that nestlings preferred large prey brought by their parents, while insects, especially moths, did 34 H. Rakotomanana, M. Nakamura and S. Yamagishi

not appear to be preferred.

Acknowledgments We are grateful to Albert Randrianjafy, the Director, and to the staff of the Botanical and Zoological Park of Tsimbazaza, for their cooperation in the realization of the this project. We thank members of Kyoto University for their essential assistance in the field: Masami Hasegawa for identifying of the prey items and Harison Rabarison for identifying the nest materials. Our sincere thanks go to Direction Generale des Eaux et Forets, Association Nationale pour 1a Gestion des Aires Protegees, for making this study possible. We also express our thanks to two anonymous reviewers for their many constructive comments and suggestions. This study was supported by a Grant-in-Aid for Scientific Research (A) of the Ministry of Education, Science, Sports and Culture (No. 11691183).

References Andersson, M. 1994. Sexual selection. Princeton University Press, Princeton, pp. 157-168. Appert, O. 1970. Zur Biologie der Vangawurger (Vangidae) Sudwest-Madagaskars. Ornithologische Beoba- chter 67: 101-133. Birkhead, T. R. & Moller, A. P. 1992. Sperm competition in birds: evolutionary causes and consequences . Aca- demic Press, London. PP. 117-145.

Conservation International. 1999. Document point zero du suivi ecologique. Conservation International , Mada- gascar, Antananarivo. 6 pp. Cramp, S. & Simmons, K. E. L. (eds.) 1980. Handbook of the birds of Europe and the Middle East and North Africa. Vol. II, pp. 160-162. Oxford University Press, Oxford. Jenkins, M. (ed.) 1987. Madagascar, an environmental profile. International Union for Conservation of Nature, Cambridge, UK and Gland, Switzerland. 27 pp. Lack, D. 1940. Courtship feeding in birds. Auk 57: 169-178. Langrand, O. 1990. Guide to the birds of Madagascar. Yale University Press, New Haven and London . pp. 292- 293. Ligon, J. D. 1999. The Evolution of avian breeding system. Oxford University Press , Oxford. pp. 259-286. Milon, P., Petter, J.-J. & Randrianasolo, G. 1973. Faune de Madagascar 35: Oiseaux. ORSTOM and CNRS , Tananarive and Paris. Morris, P. & Hawkins, F. 1998. Birds of Madagascar: a photographic guide. Pica Press, London. 244 pp. Nakamura, M., Yamagishi, S. & Nishiumi, I. 2001. Cooperative breeding in the White-headed Vanga Leptopt- erus viridis, which is endemic to Madagascar. J. Yamashina Inst. Ornithol. 33: 1-14 . Razafy, F. L. 1987. La Reserve Forestiere d'Ampijoroa: son modele et son bilan. Memoire de fin d'etude, Universite de Madagascar. Madagascar. pp. 21-38. Smith, S. M. 1980. Demand behavior: a new interpretation of courtship feeding. Condor 82: 291-295. Thorstrom, R., Andrianarimisa, A. & Rene de Roland, L.-A. 1997. In Weather at Andranobe Field Station, Western Masoala Peninsula. (ed. Watson, R.). Progress Report IV. The Peregrine Fund , Boise. PP. 127- 130. Yamagishi, S. & Eguchi, K. 1996. Comparative foraging ecology of Madagascar vangids (Vangidae). Ibis 138: 283-290. Yamagishi, S., Urano, E. & Eguchi, K. 1995. Group composition and contributions to breeding by Rufous Vangas Schetba rufa in Madagascar. Ibis 137: 157-161. Yamagishi, S., Masuda, T. & Rakotomanana, H. 1997. A field guide to the birds of Madagascar . Kaiyusha Publishers, Tokyo. 57 pp. (in Japanese and Malagasy). Breeding Ecology of Hook-billed Vanga 35

マダガスカル特産種カギハシオオハシモズVanga curvirostrisの繁殖生態

オオハシモズ科鳥類の一種カギハシオオハシモズの繁殖生態を記載し,その配偶システムを考察するため,1999年10月にマダガスカル北東部に位置するマソアラ半島,2000年10月から 2001年1月にかけてマダガスカル北西部に位置するアンカラファンチカ厳正保護区において調査を行なった。マソアラ半島では1巣,アンカラファンチカでは4巣を発見し,各番いの造巣,抱卵,抱雛及び育雛活動を観察した。巣は胸高直径390-1260mの木の地上から3-10mの高さにある二股部分にあった。造巣,抱卵,抱雛育雛とも番いと推定される2個体がほぼ同じ割合で分担して行ない,繁殖活動を手伝うヘルパー個体は観察されなかった。抱卵期間は 22-24日間,育雛期間は20-22日間で,親は無脊椎動物,ヤモリやカメレオンを主体とする小型脊椎動物を雛に給餌した。標本及び採取された死体の外部形態測定値を雌雄で比較したが有意な差は認められなかった。体サイズに明確な性差が認められず,2個体が繁殖活動を分担して行なうことから,カギハシオオハシモズの配偶システムは一夫一妻と考えた。

ラコトマナナ・ハジャニリナ:Cite 67 ha Sud: Logt 315, Antananarivo (101), Madagascar. E-mail: [email protected] 中村雅彦:上越教育大学生物学教室動物生態学研究室.〒943-8512新潟県上越市山屋敷町1 番地..E-mail:[email protected] 山岸哲:京都大学大学院理学研究科動物学教室.〒606-8502京都府京都市左京区北白川追分町.E-mail:[email protected]