NAT. NAT. HIST. BULL. SIAM Soc. 52(1): 71-79 ，2004

STRUCTURE AND COMPOSITION OF MIXED- INSECTIVOROUS FLOCKS IN KHAO YAI NATIONAL PARK

Somchai Nimnuan 1 ，Philip D. Roun d'， and George A. Galr

ABSTRACT

百le types and organization of mixed-species bird flocks were studied in semi-evergreen

forest forest on 血e Mo ・Singto Lo ng Term Biodiversity Research Plot ，Kh ao Y 凶 Nation a1 Park. A tot 叫 of 58 species of w 鎚 observed in 75 mixed 叩 ecies flocks during May- 'O ctober 2002 (average (average 12.8 individu a1 s per flωk ， 5.9 species per flock and 2.2 individu a1 s per species). Cluster 釦a1 ysis helped distinguish one well-defmed flock association consisting mostly of White-crested White-crested La ughingthrushes ( leucolophus) ， White-browed Scimitar Babblers (Pomatorhinus (Pomatorhinus schisticeps) and Red-headed Trogon (Harpactes eη幼rocephalus) ， and other medimn-sized medimn-sized birds which foraged in the ooderstorey and on 由e ground. Up to 16 species of sm a1 1 birds were a1 so foood inhabiting mixed flocks in 由巳 middle storey and canopy. 町民her S卸 dy is needed to understand more de 鈎iled aspec 包 of these flocks ，including whether discrete flocks flocks are maintained year-round ， whether recognizable “home ranges" exist for flocks ，出 e extent extent to which territory-holders participate 凶 flocks ，釦d to determine more precisely 白 e costs and and benefits of these mixed-species ass ∞iations.

Key words: Khao Yai ，bird-wave ，cluster an a1 ysis ，mixed-species flock.

副司ODUC 百ON

Mixed-species fl 'O cks 'O r “bird-waves" are defmed as aggregati 'O ns 'O f tw 'O 'O rm 'O re species species m 'O ving 泊 ac 'O'O rdinated fashi 'O n f 'O ra pr 'O l'O nged peri 'O d (Huπ '0 1987). Mixed- species species feeding fl 'O cks 'O f mainly insectiv 'O r'O us birds 釘 'e a frequent phen 'O men 'O n 泊 b 'O th 甘opical l'O wland and m 'O ntane f 'O rest. Birds f'O rm fl 'O cks ，b 'O th single-species fl 'O cks and mixed-species fl 'O cks ， either f'O r impr 'O ved pr 'O tecti 'O n from predat 'O rs (百 U 'O LLA Y & JULLIEN 1998) ，'O r p 'O ssibly because feeding benefits may accrue t 'O fl 'O ck members (Huπ '0 1988). Th e term is n'O t usually applied t 'O p 出 sive aggregati 'O ns 'O f primarily frugiv 'O r'O us birds ar 'O und stati 'O nary f'O'O d-s 'O urces such as 仕ui 出， g trees. Th ere have been relatively few studies 'O f mixed-species fl 'O cks in S 'O utheast . Mixed-species flocks in Kh a 'O Yai were said by MCCWRE (1974) t 'O include mainly Campephagidae ，Aegi 血血idae ，Zo s町'O pidae ， and Nectariniidae. M 'O re recently ，K 町 G & RApPOLE (2001a) studied mixed-species fl 'O cks 加 dry dipterocarp f'O rest (Myanm 釘') and indicated that there were 由民e principal types 'O f fl 'O cks c'O nsisting 'O f laughingthrush fl 'O cks ，warbler fl 'O cks 組 dw 'O'O dsbrike fl 'O cks.

'Oep 釘伽lent of Biology ，Faculty of Science ，M a1u dol University ，Rant a 6 Road ， Bangkok 10400 ， Th ailand. 2KingMon 依ut's University ofTechnology 百四buri ，School of Bioresources & Technology ， 83 Moo. 8 百m 凶鑑n， Bangkhootien ， Bangkok 10150 ，百lailand. Received Received 4 Au 伊 st 2∞ 3; accep 旬d 10 July 2004.

71 72 SOMCHAI NIMNU 釧， PHnJP D. ROUND ，AND GEORGE A. GALE

We focused our attention on the types and organization of mixed-species flocks found in 甘opical evergreen forest 泊Kh ao Yai National P釘k. Specifically we wished to determine (1) (1) which species associated in mixed-species feeding flocks; and (2) whether any particular associations associations among species could be identified.

STUDY AREA

Th e study was conducted on 白eMo ・singto Long Term Biodiversity Research Plot ， Kh ao Yai National Park (1 4 0 26'N ，10I 0 22'E). 百le plot covers 組 area of 30 ha in 由e contiguous contiguous ca. 2000 km 2 forest area in 出.e park ，and has been s町 veyed and mapped on a 20-m grid. Th e locations of all 慨 sgrea 町出an 10 cm dbh have been plo 削 (BROC 臨 L胤 N 1998). 百le plot is dominated by series of ridges and valleys with 佃 elevation range of 723-817 m above sea leve 1.百 le vegetation is mainly mature evergreen forest with small 釘 'eas of regenerating secondary fores t. Pre cipitation is 200 0-- 3∞o m rn/ ye 釘 (Royal Forest Depar 加 lent da 旬)， most of which falls during May to October.

METHODS

Data Data were collected during May to October 2002. One 値血 rre 伺e-t 旬o-fl 白ou 町r-da' 可yv吋is 討副i託t wa 郁s madepe ぽr month during June to September ， with approximately 10 days being allocated for fieldwork fieldwork during May and October. Observations were made by one observer (SN) walking established established trails 佐賀 ough the forest ，listening for vocalizations (mobbing ， alarm calls ， contact contact calls) and watching for movement. All species of birds encountered were identified ， using using LEKAGUL & ROUND (199 1) and counted ，and recorded as either associating with a mixed-species mixed-species flock ，moving singly ， or in single-species flocks. Wh en a flock w 制 located ， it it was followed for as long 拙 possible ，and 白 .e position of the flock was noted using the established established grid. 百le number of individuals per species ， for a1l species 泊 each flock ，was coun 飽d 血 d 血ispro 白 ssw 部 repeated every 15 minutes. Between ∞ unts selected individuals of of as many species 部 possible were categorized 邸 to feeding s国側m (height above ground). ground).

Each species w ，描 scored for percentage occurrence in to 凶 number of flocks observed ， 組 dme 釦 number of individuals per flock. Associations between s戸 cies were scored 部 either either (1) present or (0) absent and a cluster analysis was performed on those species

田 C 町由g 泊 more 由加5% of the flocks using unweigh 飽dpair 圃 group amalgamation (出虫 age) rules ， with the Pearson r correlation coefficient as the distance me 踊 ure. Statistica 5.5 w 部 used used to perform 出 is analysis. Species ぬxonomy 佃 d nomenclature throughout 白is account follows follows ROUND (2000). Scientific names of all flock-participating species are given 泊 Table Table 2.

RESULTS

A total of 63 species of birds was encountered 血roughout the study period. Of these ， 58 species were recorded apparen t1 y participa 出港泊 associations of two or more species 佃 d thus considered to be in mixed-species flocks (Table 2). 百le five species recorded MIXED-SPECIES INSECTIVOROUS BIRD FLOCKS 73

that that did not participate were Mountain Im perial Pigeon (DucuZa badia) ，Blue Pitta (Pit ω cyanea) ， Hill Myna (GracuZa religiosa) ，Black-crested Bulbul (Pycnonotus meZanicterus) 叩 d Stripe- 白roated Bulbul (P. finZaysoni). A total of 75 mixed-species foraging flocks was encountered during 16 days of observation. 官le average flock size w 田 12.8 individuals per flock. On average there were 5.9 5.9 species per flock and 2.2 individuals per species (Table 1). Nineteen Nineteen species of birds occun 吋泊more than 10% of the flocks ，and 37 species in more 血an 5%. Wh ite-bellied Yuhina and warblers ，Phylloscopus spp. ，were 血e most frequent frequent participants in mixed flocks ， each found at a 企equency of 41 %. However ， the Phylloscopus Phylloscopus warbler total was probably con 凶buted by at least two species ，Two-barred Warbler (P. pZumbeitarsus) and Yellow-browed Warbler (P. inornatus) ，which the observer could could not reliably distinguish. Th e other most 合'equent species found in mixed-species flωks were Greater Racket-tailed Dr ongo (39%) ， Black-naped Monarch (37%) ，Wh ite- crested crested Laughingthrush (35%) ，Whi te-browed Sc 加 it 紅 Babbler (28%) ，Red-headed Trogon (24%) ，L 釘 ge Scimitar Babbler and S佐iped Tit Babbler (each 20%; Table 2). Rosy predominated in terms of the number of individuals per flock (4.75 individuals individuals ).百 le s住ongest s戸 cies associations were between Wh ite-crested Laughingthrush and Wh ite-browed Scimitar Babbler (Pearson correlation r = 0.77 ，P < 0.001); and between Le sser Necklaced Laughingthrush 組 d Gre en Magpie (r = 0.74) ，Whi te-browed Scimitar Babbler Babbler and Red-headed Trogon (r = 0.73) ，Wh ite-crested Laughingthrush and Large Scimitar Scimitar Babbler (r = 0.67) ，Whi te-crested Laughing 出rush and Gre en Magpie (r = 0.66) ， Wh ite-crested Laughingthrush and Le sser Necklaced Laughing 出rush (r = 0.60). All these correlations correlations were significant (P < 0.001). 百lese six species ，toge 出er with a seventh species ， Laced Woodpecker ，formed a moderately distinct and identifiable cluster (Fig. 1). All 白ese species species were medium to large inhabitants of middle storey and understorey ， with the laughingthrushes laughingthrushes feeding mainly on 出e ground. Th e cluster analysis showed a dichotomy between 14 species of medium to large birds ， including those mentioned above，佃 d 23 species of smaller birds ，most of which inhabited inhabited middle and upper storey and canopy. Possibly 出 many as 16 species of these smaller smaller birds showed a tendency to cluster together ， while within these a number of species-pairs species-pairs showed apparent association (e.g. ，Scarlet Mini vet with Bar-winged Fl ycatcher- shrike ，r = 0.73 ，P < 0.001; Gre enish Warbler with Sultan Tit ，r = 0.58 ，P < 0.001 ，佃 d Wh ite-bellied Yuhina with Black 叫 ed Monarch ，r = 0.57 ，P < 0.001; 均 .2). Th ere w 酪 a tendency for the flycatcher-shrike ， ， Sultan Tit and leaf warblers to f回quent the canopy ， while the yuhinas and Black-naped Monarch fおquented the upper-middle storey. However ，there 紅 e probably too few observations at this stage to draw any detailed conclusions conclusions about the composition of small-bird flocks. A third ， rather poorly defmed cluster included Ashy Drongo ，Plain-tailed Warbler ， Pu ff- 血roated and Grey-eyed Bulbuls ， Hill Blue Fl ycatcher ， Dark-necked Tailorbird and 釦 iped Tit Babbler and may merely represent speci 回出at do not otherwise fit in 旬組y clear clear group 泊g.τ 'h e bulbuls were bo 出合ugivorous and insectivorous ，and sometimes occuned in in single-species flocks and sometimes apparently joined mixed flocks. Th is consistent with with the observations of the other studies in the tropics (MCCLURE 1967 ，H U'IT O 1987) in terms terms of passive aggregations of mixed-species foraging flocks. Th e insectivorous Hill Blue 日ycatchers were strongly territorial and this may res 凶 ct 白eir p釘 ticipation 加 flocks should should territory their boundaries not coincide with the foraging range of the flock. 74 74 SOMCHAI NIMNUAN ， PHILIP D. ROUND ，AND GEORGE A. GALE

Table Table 1. Flock-sizes and species diversity at Mo ・Singto sωdy area (n = 75)

Variable Variable Average Range Number of individuals 12.8 2-4 5 Number of species 5.9 2-15 Number of individuals per species 2.2 1-10

Table Table 2. Li st of birds that occurred in flocks listed in order of frequency of encounters.

O ∞町 rence in flocks Total Total Species Species Average Abbreviation Frequency Frequency number of individuals individuals individuals ite-bellied Wh ite-bellied Yuhina (Yuhina zantholeuca) 0.41 2.23 69 YUH Le af Warbler spp. (Phylloscopus plumbeitarsus ，P. inornatus) 0.4 1 4.3 9 136 GWA Greater Greater Racket-tailed Drongo (Dicrurus paradiseus) 0.3 9 1.3 1 38 GDR Black-naped Black-naped Monarch (Hypothymis azurea) 0.3 7 1. 89 53 MON ite-crested Wh ite-crested Laughingthrush (Garrulax leucolophus) 0.3 5 4.62 120 WLG White-browed White-browed Scimitar Babbler (Pomatorhinus schisticeps) 0.28 2.00 42 WSB Red-headed Red-headed Trogon (Harpactes erythrocephal ω) 0.24 1.3 3 24 RHT Lar ge Scimitar Babbler (Po. 朋 torhinus hypoleucos) 0.20 1. 80 27 LSB S凶ped Tit Babbler (Macronous gularis) 0.20 2.80 42 STB Plain-tailed Plain-tailed Warbler (Seicercus soro. け 0.1 7 1. 77 23 PWA Green Green Magpie (Cissa chinensis) 0.16 1. 67 20 GMG Blue-winged Blue-winged Le afb 凶 (Chloropsis cochinchine 附 is) 0.1 6 1. 75 21 BWL sser Le sser Necklaced La ughingthrush (Garrulax monileger) 0.1 5 1. 55 17 NLG Green- billed Malkoha (Phaenicophaeus tristis) 0.1 5 1. 00 II GBM Paradise-flycatcher Asian Paradise-flycatcher (Terpsiphone paradisi) 0.1 3 1. 00 10 APF Orange 批 0.12 1. 22 II OBT Black-winged Black-winged (Coracina melaschistos) 0.12 1. 89 17 BCS Grea 低 rFl arneback (Ch 明 ocolaptes lucidus) 0.11 1. 63 13 GFB La ced Woodpecker (Picus vittatus) 0.1 1 1. 50 12 LWO Ashy Ashy Drongo (Dicrurus leucophaeus) 0.09 1. 29 9 ADR GI 官y-headed Fl ycatcher (Culicicapa ceylonensis) O.ω 1. 57 II GFY Emerald Emerald Dove (Chalcophaps indi ω) 0.08 1.1 7 7 EMD Scarlet Scarlet Minivet (Pericrocotus flammeus) 0.08 2.5 0 15 SCM Bar-winged Bar-winged Flycatcher-shrike (Hem 伊us picatus) 0.08 3. 17 19 BFS Greater Greater Yellownape (Picus flavinucha) 0.07 1. 60 8 GYN Green-eared Green-eared Barbet (Megalaima faiostricta) 0.07 1. 80 9 GBR Black-naped Black-naped Oriole (Oriolus chinensis) 0.07 1. 20 6 BNO Sultan Sultan Tit (Melanochlora sultanea) 0.0 干 4.20 21 SUT sser Le sser Racket-ta i1 ed Drongo (Dicrurus rem 砕け 0.07 1. ω 5 LDR Asian Asian Fa 町 Bluebird (lrena puella) 0.05 2.25 9 AFB Dark-nacked Dark-nacked Tailorbird (Orthotomus atrogularis) 0.05 1. 75 7 DNT G 問:y -e y凶 Bulbul (lole propinq 即) 0.05 2. ∞ 8 GBU Pu ff. ・血 roated Bulbul (Alophoixus pallidus) 0.05 2.7 5 11 PBU Hill Hill B1ue Fl ycatcher (Cyornis banyu. 刷 s) 0.05 1. 25 5 HFY Sulphur-b 陀お飽 d Warbler (Phylloscopus rickett l) 0.05 1. 50 6 SWA Rosy Rosy Minivet (Pericrocotus roseus) 0.05 4.7 5 19 ROM Black-throated Black-throated Sunbird (Aethopyga saturata) 0.05 2. ∞ 4 BSU MIXED-SPECIES INSECTIVOROUS BIRD FLOCKS 75

Table 2. (continued). Occurrence in flocks Total Species Average Abbreviati on Frequency number of individuals individuals Little Spiderh unter (Araclmothera longirostra) 0.04 1.33 4 LSP Blyth's Lear Warbler (Phylloscopus reguloides) 0.04 1.67 5 BWA Red Junglefowl (Gallus gallus) 0.04 1.33 4 RJF Pa le-l egged Lear Warbler (Phylloscopus tenellipes) 0.04 2.00 6 PLW Black-throated Laughingthrush (Garmlax chinensis) 0.03 1.00 2 BLG Black-and-bufr Woodpecker (Meiglyptes jugularis) 0.03 1.00 2 BWO Moustached Barbel (Megalaima incognita) 0.03 2.00 4 MBR Abbott 's Babbler (Trichasroma abboui) 0.03 2.00 4 AB B Great lora (Aegithina lafresnayei) 0.03 2.00 4 lOR Brown-rumped Mini vet (Pericrocotus camonensis) 0.03 2.00 4 BRM White- rumped Shama (Copsyclws ma/abaricus) 0.03 1.00 2 WSH As hy Bu lbul (Hypsipetes flavala) 0.03 2.00 4 ABU Silver-b reas ted Broadbi ll (Serilophus lwwtus) 0.03 2.50 5 SBB Long-tailed Broadbill (Psarisomus dalhousiae) 0.03 4.00 8 LBB Banded Kingfisher (Lacedo pnlchella) 0.0 1 1.00 I BKF Blue-eared Barbel (Megalaima australis) 0.01 4.00 4 BBR Purr-throated Babbler (Pellomeum mficeps) 0.0 1 1.00 I PTB Radde's Warbler (Phylloscopus schwarzi) 0.01 1.00 I RWA Banded Broadbi ll (Eurylaimus javanicus) 0.01 2.00 2 BBB Si lver Pheasant (Araclmothera /ongirostra) 0.01 1.00 I SPH Oriental Pied Hombill (Anthracoceros albirostris) 0.0 1 3.00 3 OHO

1.2

1.0 .. I 0.8 l - I .. Q) I '-' J c I u;"' 0.6 1 .. .. 0 Q) Ill) Ol ""'"'c 0.4 ::J ~ 0.2 ~

0.0

Figure I. Cluster diag ram for 37 species (those present in 2: 5% of the flocks) using unweighted pair-group averaging amalgamati on (l inkage) ru les and Pearson r correlation coefficient as di stance measure; y­ ax is is 1-r. 76 SOMCHAI NJMNUAN, PHILIP 0 . R OUND, AND GEORGE A. G ALE

20 18 16 • 14 • • (/) Cll '(j 12 • Cll • • Q. (/) 10 • •• • ••• • .fl 8 0 • •• • • 1- •• •• • • 6 • ••• • •••••• 4 ••••••• •• •• 2 ••••• 0 0 5 10 15 20 25 30 35 40 45 50 Flock-size

Figure 2. Correlation between total number of species and flock-size (total number of individuals) found in fl ocks (r = 0.63, P < 0.001).

4.00

iii 3.50 0 Cll • Q. • ~ 3.00 • Cll • Q. • • • • • ..!!! 2.50 • • • • • • • ~ • • • • ::J • • • • "C • • • 2.00 • • • • • • :~ • "C • • • • c • • • •• • ..... 1.50 • • • 0 • • &.. • Cll ..Q 1.00 • • E z::J 0.50

0.00 0 10 20 30 40 50 Flock-size

Figure 3. Correlation between number of individuals per species and flock-size (total number of individuals) found in flocks (r = 0.54, P < 0.00 I). MIXED-SPECIES MIXED-SPECIES INSECTIVOROUS BIRD FLOCKS 77

There There was a significant correlation between the number of individuals and number of species species in mixed-species flocks (r = 0.63 ，P < 0.001 ， Fig. 2) such that large flocks usually contained contained more species of birds 白血smaller flocks. Th ere was also a less marked ， but still significant ，correlation between the number of individuals per species and flock-size (r (r = 0.54 ，P < 0.001 ， Fig. 3). 官 lere was no significant correlation between total flock-size and the number of two of the core flock species ，Wh ite-crested Laughingthrushes (r = 0.36 ， P = 0.07) and Wh ite-bellied Yuhinas (r = 0.01 ，P = 0.96) although there was a sigr 司自 cant correlation correlation between total flock-size and the number of Phylloscopus warblers participating (r (r = 0.84 ，P < 0.001). Th ere were seven species recorded with flocks for which the f同quency of occurrence was very low (1 %) and the associations with the flocks unproven or accidental. 百lese were Banded Kingfisher ， Blue-eared Barbet ， Pu ff-throated Babbler ， Radde's Warbler ，Banded Broadbill ， Silver Pheasant and Oriental Pied Hombill.

DISCUSSION

百le compositions of mixed-species flocks in Kh ao Yai were somewhat similar to those those in a very different forest type ， dry dipterocarp forest ， in Myanm 釘 (KING & RAl' POLE 2001a). 官 lere ，白ree principal types of flocks were detected: one consisting mostly of Common Woodshrike (Tephrodornis pondicerianus) ，Small Minivet (Pericrocotus cinnamomeus) cinnamomeus) and Wh ite-browed F 組 tail (Rh 伊idura aurolea); a second type consisting mainly mainly of small birds such as Arctic Warbler (Phylloscopus borealis) ，Dusky Warbler (P. fuscatus) fuscatus) and Radde's Warbler (P. schwarzi); and a third type which was generally centered around around Greater Necklaced Laughingt 胎ush (Garrulax pectoralis) and Le sser Necklaced Laughing 白rush (G. monileger). Th e relatively small number of individuals per species found during the present study suggests suggests that most were represented in flocks by single individuals ，pairs ， or family groups. 官lis was similar to the findings of POWELL (1 979) and K 凹 G & RAPPOLE (2001a). 百le relation relation between total flock-size and number of species was stronger than the relation between flock size and average number of individuals per species. Fl ocks grew more by adding adding further species than by adding further individuals per species. Studies elsewhere (e.g. ，POWELL ， 1979; MUNN & TERBORGH ， 1979) have shown that te 凶 tory holders join flocks; flocks; usually remaining with the flock for only as long as it remains within their territory. 官lis would lirnit the number of individuals of any one species participating at any one time. time. In Kh ao Y 剖， for example Hill Blue Flycatchers ，which are strongly territorial ，would be res 位icted in 曲is manner. Additionally ，if a flock already contains several individuals of one species ， then other ，conspecific ，individuals might do better to avoid 白e flock ，and forage forage elsewhere in order to avoid close competition. 百le flocks in Kh ao Yai were dis 位ibuted in different foraging strata ，which is consistent with with the findings of other studies (MCCLU 阻， 1967). MCCLU 阻 (1967) also found that there there were more flocks in August ，when there would be m 佃 y fledged young ，and fewer flocks flocks between January and July when a majority of the birds 釘 'e breeding. However the present present study was of too short a duration to examine the effects of seasonality on flocking behaviour. behaviour. 78 78 SOMCHAI NIMNUAN ，PHI Ll P D. ROUND ，AND GEORGE A. GALE

Some app 釘 ent flock and species-pair associations (e.g. ，Plain-tailed Warbler with Ashy Drongo; Grey-eyed Bulbul with Dark-necked Tailorbird) may be spurious. First ， there there may be too few observations to provide statistically valid associations about them. Secondly Secondly some species may not truly associate ， but merely use 出e same microhabitat ， such as as Whi te-rumped Shama and Abbott's Babbler ， which both appeared to be associated with rattan rattan clumps. In addition there is the problem of statistical type 2 eηors: with a 37 x 37 correlation correlation matrix some apparent associations might be expected to be spurious (DEVORE & PECK ， 1990). Th e association of Greater Racket-tailed Drongo ，which was frequently associated with with mixed-species flocks of laughingthtushes ，invites special questions ， since the drongo maybeaklepωp 釘 asite which steals food flushed by the laughingthrushes (K 別 G&RApPOLE ， 2001b.) 百lis was the su 吋ect of a sep 訂 ate study (DHANASARNPAIBOON & ROUND ， 2004)

Th is study raises several other interesting questions for further research. For ex 創 nple ， bo 出 residents and migrants join flocks. However most observations were made outside the migratory migratory season (May to October) ， and it is possible that Phylloscopus warblers and other migrants migrants might be even more frequent if observations were made throughout the winter. Further Further study is also needed to understand the mechanism of flock formation: whether discrete discrete flocks are maintained ye 訂 -round ， and whether recognizable home-ranges or territories territories exist for flocks. For example ， four different Wh ite-crested Laughingthrush flocks were thought to inhabit the Mo-Singto plot ， each of which tended to be found in the same 紅白s on successive days. However ， at the time of this study ，colour-marking ， to enable individuals individuals to be recognized and their movements tracked ，had not yet commenced. Finally ， further further research is needed on the associations of small mammals with mixed-species bird flocks. flocks. At least three species of squi 汀 'els (Burmese Striped Tree Squirrel Tamiops macclellandi ， Variable Squirrel Callosciurus finlaysoni ，and Grey-bellied Squi 町 el C. caniceps) caniceps) appeared to keep up with the birds ，especially flocks of laughingthrushes ， as they moved through the fores t. This might indicate that they benefit from flocking behaviour in the the same way as do the birds ， as previously suggested by MCCLURE (1 967).

ACKNOWLEDGMENTS

We 出創Ik Dr. Warren Y. Brockelman and the staff of the Kh ao Yai gibbon project for allowing allowing tempor 訂 y use of their accommodation ， and for their help and suggestions in fieldwork. fieldwork. Mr. An drew J. Pierce also gave much advice. We 自白Ik Mr Pr awat Wohandee ， Superintendent Superintendent of Kh ao Yai National Park ， and the Department of National Parks ，Wildlife and and Plant Conservation for permitting us to collect observations in Kh ao Yai National P訂k. SN would like to th 担Ik Wuttipat Raksakom and Supatcharee Dhanasampaiboon for their their help and encouragement in fieldwork ， and his family for the encouragement and support. support. This work was ca 灯台 d out as a senior project submitted in partial fulfillment of the the requirements for B.Sc. (Biology) ， Faculty of Science ，Mahidol University. MIXED-SPECIES INSECTIVOROUS BIRD FLOCKS 79

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