Because of seasonal changes in food sources and weather conditions in the northern hemisphere, many raptors make long-distance movements back and forth between breeding and wintering areas each year (Kerlinger 1989). The migration routes, magnitude, and timing may vary according to species. Such phenomena have encouraged the establishment of migration watchsites in many countries (Zalles and Bildstein 2000), particularly at places where birds congregate and can be seen easily. In the past, many migratory raptor watchsites were established as a result of concerns over human persecution of these birds (Bildstein 2006). Over the years, the fluctuations of raptors observed through long-term migration counts have helped researchers assess the status of species' populations, as well as understand the impacts of human activities (such as the use of agricultural chemicals) on migratory raptors (Bednarz et al. 1990), even when the number of migratory birds was small (Bildstein 1998). At present, there are nearly 400 migration watchsites in over 89 countries on six continents, with the highest densities found in Europe and North America, where monitoring can be dated back to the first half of the 20^th century (Zalles and Bildstein 2000, Bildstein 2006).

There are 66 complete and partial migratory raptors on continental Asia (Zalles and Bildstein 2000, Yamazaki et al. 2012). At wintering or stopover sites, migratory raptors can be seen, often in large numbers, throughout many parts of Southeast Asia including Thailand, Vietnam, Malaysia, Indonesia, and the Philippines depending on their migration routes (Higuchi et al. 2005, Shiu et al. 2006, Yamaguchi et al. 2008, Germi et al. 2009). Over the last decade, there has been an increase in the number of migratory raptor watchsites (e.g., DeCandido et al. 2004a, 2008, DeCandido and Nualsri 2009) in Southeast Asia from which raptor count data are collected primarily by volunteers. Because of the counts and the increased local awareness, many watchsite locations have since become protected. Moreover, the establishment of the Asian Raptor Research and Conservation Network (ARRCN) exemplified joint efforts in studying and conserving the migratory and resident raptors in the region.

As part of the East Asian–Australasian flyway, Malaysia serves as both a wintering and stopover site for many migratory birds, including raptors. Tanjung Tuan is the most prominent watchsite in the country for counting migratory raptors that are heading northeast from Sumatra, Indonesia, in spring during their return migration. Like many other watchsites in different parts of the world (Bildstein 2006), Tanjung Tuan is a peninsula, which shortens overwater crossing for the migrating birds. Although the movement of migrants through Tanjung Tuan has been recognized since the 1950s, only a few published works with detailed accounts of the migration, most involving shorter observation periods, are available (DeCandido and Allen 2000, DeCandido et al. 2004b, 2006), whereas other data are in the form of observation reports (e.g., White 1961, Medway and Nisbet 1965, Wells 1990). We describe the magnitude and migration timing of migratory raptors as well as their flight behavior based on the annual standardized counts made at Tanjung Tuan in 2009 and 2010. Our study highlights the importance of maintaining migration counts and protecting these migration locations in Southeast Asia.

Methods

Study Site.

Designated as an Important Bird Area (IBA), Tanjung Tuan (2°24.4′N, 101°55.3′E; Fig. 1) is a promontory of 95-m elevation that stretches out 1.2 km into the Straits of Malacca (Yeap et al. 2007). The rocky promontory is surrounded by the Tanjung Tuan Forest Reserve, a Virgin Jungle Reserve of 75.9 ha located in Melaka state on the southwestern coast of Peninsular Malaysia. The area has undulating terrain dominated by trees from the Myrtaceae family (Mat-Salleh et al. 2003) and receives an annual rainfall of 3230 mm with a mean temperature of 32°C.

Figure 1. 

Location of Tanjung Tuan, Peninsular Malaysia (Google Earth,  www.earth.google.com).

The Rachado Lighthouse, built in 1890, stands at the tip of the promontory overlooking the Straits of Malacca. The peninsula provides the shortest distance (ca. 38 km) for migrating raptors moving across the Strait between Sumatra (Rupat Island) and Peninsular Malaysia (Zalles and Bildstein 2000). In addition to other non-raptor migrants (DeCandido et al. 2004b), at least nine migratory raptor species are recorded at Tanjung Tuan each year (Yeap et al. 2007) including three complete migrants, i.e., Oriental Honey-buzzard (Pernis ptilorhyncus), Chinese Goshawk (Accipiter soloensis) and Grey-faced Buzzard (Butastur indicus).

In March 2000, the Malaysian Nature Society (MNS) organized the first Raptor Watch Week at Tanjung Tuan in response to a potential development threat to its forest habitat. Subsequently, Raptor Watch Week became an annual event to promote public awareness about the importance of the area as a stopover point for migrants. Since then, raptor counts have also been initiated by the MNS, with the main counters being volunteer birdwatchers. Over the years, the protocols of the migration count have been improved and standardized, and this has provided more information on the magnitude, timing, and seasonality of raptor migration at the site.

Results

The numbers of migratory raptors recorded during the two nearly full-season counts at Tanjung Tuan were 37 615 birds (11 312 individuals/100 hr; Table 1) in 2009 and 72 277 birds (15 526 birds/100 hr) in 2010. Eleven species were recorded in 2009 and 10 species in 2010. The Oriental Honey-buzzard accounted for a substantial proportion of the total count for the two years, 85.9 ± 2.9% (mean ±SD; 30 000–60 000 individuals per season), followed by Black Baza (Aviceda leuphotes; 8.7 ± 3.8%), Chinese Goshawk (3.0 ± 2.0%), Japanese Sparrowhawk (Accipiter gularis; 0.7 ± 0.8%) and Grey-faced Buzzard (0.1 ± 0.1%). Other migrants appeared to be low in numbers, i.e., Peregrine Falcon (Falco peregrinus), Osprey (Pandion haliaetus), Booted Eagle (Hieraaetus pennatus), Black Kite (Milvus migrans), Eastern Marsh-Harrier (Circus spilonotus) and Pied Harrier (Circus melanoleucos).

Table 1. 

Raptor counts and passage rates by species at Tanjung Tuan, Peninsular Malaysia (2009–2010).

When data for all species were pooled, bulk (central 80%) passage dates covered a period of 29–38 d commencing on the last week of February with an average median passage date in the middle of March (Table 2). The bulk passage of Oriental Honey-buzzard occurred between 22 February (the earliest) and 1 April (the latest, i.e., ranging between 30–39 d with the median passage falling on 15 March and 14 March, respectively) for the two years. Similarly, the Grey-faced Buzzard arrived about the same period, although the passage period was shorter: 17–20 d. The bulk passage of Black Baza, Chinese Goshawk, and Japanese Sparrowhawk occurred in the middle of March and the passage periods of these birds took from 10 to 16 d.

Table 2. 

Central 80% passage periods and median passage dates for migratory raptors counted at Tanjung Tuan, Peninsular Malaysia (2009–2010).

For Oriental Honey-buzzard, daily migration started at 0900–1000 H and the migration activity increased considerably and reached a peak at 1200–1300 H before it gradually decreased and ended at 1700 H (Fig. 2). The birds often arrived low (about 30 m aboveground) in large flocks (328.7 ± 13.6 birds per flock). Both Black Baza and Chinese Goshawk tended to show a low activity during the early hours of the day and numbers peaked later at 1400–1600 H. For other raptors that passed through Tanjung Tuan, numbers were too low to indicate any obvious activity pattern across the day.

Figure 2. 

Daily temperature (°C) and activity patterns of three major migratory raptors (in their respective proportions and means ± SE) recorded at Tanjung Tuan, Peninsular Malaysia (2009–2010). The proportions of migrants were calculated based on the hourly number of birds recorded for a particular species relative to the total number of individuals recorded for that species during the entire migration count.

Results of Pearson correlation analysis indicated that the number of Oriental Honey-buzzards was unrelated to temperature recorded on an hourly basis (r  =  0.001, P  =  0.997). In contrast, the height of flight for the birds was positively correlated with the hourly temperature (r  =  0.241, P  =  0.026). The average daily temperature at the watchsite was 32.1 ± 0.1°C. The number of Oriental Honey-buzzards counted per hour showed a trend toward a negative relationship with wind speed, although the relationship was not statistically significant (r  =  −0.101, P  =  0.063). On average, tailwinds from the southwest (3.36 km/hr ± 0.43) and west (4.60 km/hr ± 0.77) rose at 1200–1300 H, increased until 1400–1600 H, then decreased again at 1700 H (Fig. 3).

Figure 3. 

Number of hours during which different wind directions were encountered at Tanjung Tuan throughout the migration count.

The highest counts for Oriental Honey-buzzards for both years were made during southwest and western winds (Fig. 4). However, the result of a one-way ANOVA indicated no significant difference in the numbers of Oriental Honey-buzzards counted during different wind directions recorded at the watchsite (F_7,281  =  1.835, P  =  0.081). Similarly, daily rainfall was unrelated to the numbers of Oriental Honey-buzzards observed (r  =  −0.138, P  =  0.188).

Figure 4. 

Number of Oriental Honey-buzzards counted during different wind directions, measured from the migration watchsite at Tanjung Tuan, Peninsular Malaysia (2009–2010).

Discussion

The first two years of a nearly full-season count of migratory raptors confirmed that Tanjung Tuan is an important migration location for these birds. Both complete as well as partial migrants from the northern hemisphere passing through Peninsular Malaysia were seen at Tanjung Tuan, with their numbers and arrival times varying by species. Except for the relatively lower number of species, the bulk passage (ranging from 37 615 or 11 312 birds/100 hr in 2009 to 72 277 or 15 526 birds/100 hr in 2010) was comparable to the count conducted in southern Thailand, which is geographically a bottleneck for migrants (DeCandido and Nualsri 2009). In terms of species, the major passages were made up of Oriental Honey-buzzards (30–39 passage days) followed by Black Bazas and Chinese Goshawks (10–12 d). The major species recorded at Tanjung Tuan were similar to those recorded in autumn (DeCandido et al. 2004a) and in spring in southern Thailand (DeCandido and Nualsri 2009), but with different proportions of species, indicating that different raptors are using different migration routes, which are not yet completely understood.

The daily arrival of migrants tended to differ according to species with the number of Oriental Honey-buzzards peaking around midday (1200–1300 H), followed by Black Bazas and Chinese Goshawks peaking later in the day. The Oriental Honey-buzzards were observed in flocks forming a steady stream from the direction of Sumatra. The general flight pattern of the birds was a combination of flapping and soaring over the sea (Yamaguchi et al. 2012), but the flight pattern was mainly soaring as soon as they reached land. The latter flight behavior was presumably associated with slope soaring as the birds used the horizontal winds that hit and deflected over the promontory. Occasionally, the birds were also observed “kettling” or circling using thermals over the sea.

At Tanjung Tuan, the arrival of Oriental Honey-buzzards at lower heights and earlier in the day than the other migrants may be explained by this species' ability to use both soaring and flapping flight ability, thus rendering them not directly dependent on thermals during migration; in this, they are similar to their western Asia counterpart, the Western Honey-buzzard (Pernis apivorus; Bildstein 2006). However, it should be noted that the height of the flight for the birds was positively correlated with hourly temperature, suggesting the use of thermals generated during the day that lifted the birds higher, possibly aiding them during migration when crossing the Straits of Malacca. A negative trend between the numbers of the birds counted per hour and wind speed may imply that strong winds may disturb the thermals needed for migration. Indeed, many birds were seen panting while crossing the water. There were also cases of birds crashing into trees to perch and rest immediately upon arrival at the lighthouse and, in some cases, falling into the sea. These observations suggested that birds do rely on thermals, at least to a certain extent, to lift them higher while minimizing the use of flapping flight to move across open water. In addition, the ability of Oriental Honey-buzzards to cross over the East China Sea (650 km) during their southbound migration was demonstrated to be weather-assisted (Yamaguchi et al. 2012).

On the other hand, the peak arrival of Black Bazas was after midday (1400–1500 H), with birds soaring fairly high and moving in large and tight flocks of 250 birds or more. The later arrival of Black Bazas, which have broad and rounded wings, may be associated with their soaring behavior that requires the updraft generated by thermals. Unlike Black Bazas, the Chinese Goshawks' flight pattern involved mainly flapping flight at a higher elevation. They often moved in large and loosely-formed flocks of about 200 individuals and occasionally in smaller groups or as single individuals. Individuals were seen flocking following the gradual buildup of thermals and soaring well away from the lighthouse. Chinese Goshawk arrival peaked at 1500–1600 H and this interval coincided with the highest temperatures of the day on average, suggesting that these accipiters use thermals during their passage. Similar flight behavior was seen in Japanese Sparrowhawk, which occurred in lower numbers and mostly consisted of single individuals. Described as one of the most oceanic of all long-distance migratory raptors (Bildstein 2006), Grey-faced Buzzards recorded at Tanjung Tuan were much less common than the three species mentioned above (i.e., less than 0.2% of the totals counted for the two years). The Grey-faced Buzzards that passed through Tanjung Tuan flapped their wings constantly and flocking was rare.

Based on observations made at Tanjung Tuan, the frequencies of southwestern and westerly winds were relatively high during and after midday (Fig. 3) and this coincided with the peaks of the three major spring migrants. However, we failed to detect any significant difference in the numbers of Oriental Honey-buzzards relative to different wind directions, possibly due to the small sample size. Similar to the findings of DeCandido et al. (2006), we found the birds made landfall during light to moderate winds of less than 15 km/hr (Malaysian Nature Society unpubl. data). Nonetheless, at local scale, we believe that the combination of both thermals and tailwinds may facilitate movement across the Straits of Malacca.

Compared to their Nearctic and Palearctic counterparts, raptors of the East Asian–Australasian flyway are still poorly known (Kirby et al. 2008, DeCandido and Nualsri 2009), with only a few studies to date (Higuchi et al. 2005, Shiu et al. 2006, Yamaguchi et al. 2008, Germi et al. 2009, Yamaguchi et al. 2012). Surveys by raptor specialists have indicated that the current conservation status of as many as 17 (33% of the total of 51) migratory raptors in the region is considered unfavorable, and the status of many species remains uncertain (Goriup and Tucker 2007).

Fortunately, over the last decade, an increasing number of migration watchsites have been established in this region (such as Nijman 2001, Tordoff 2002, DeCandido et al. 2004a, Germi 2005, Germi et al. 2009, Sun et al. 2010) and migration counts were also made possible due to the joint efforts of birdwatchers and raptor biologists. We recommend the continuation of consistent monitoring of migratory raptors at Tanjung Tuan and the strengthening of collaborations with other raptor migration watchsites along the flyways through sharing of monitoring data. Continental analysis of migration data may help in the identification and protection of stopover and wintering sites for these birds. Long-term monitoring of migratory raptors at different watchsites along the migration routes will aid in detecting the fluctuations in the raptor populations (e.g., based on Raptor Population Index; Farmer and Hussell 2008), if any, and the associated threats to these birds.

Compared with long-established migration watchsites, including Hawk Mountain Sanctuary in Pennsylvania, U.S.A., with migration counts that date back to 1934, Tanjung Tuan is in its infancy in such monitoring work. Nonetheless, it is worth highlighting that the Chumphon Raptor Centre located in southern Thailand, a bottleneck for raptor migration (DeCandido et al. 2004a), has been bestowed the title “Hawk Mountain of Asia,” marking the first step toward the conservation of Asian migratory raptors and their stopover as well as wintering sites. The establishment of the Chumphon Raptor Centre came about from local government support for a local raptor enthusiast's idea of building the center and serves as a good role model for other developing countries such as Malaysia in achieving conservation goals by educating the public about migration and the need for long-term migration monitoring work.