Impact of Migratory Birds on Resident Terrestrial Birds in Southeast Asia: A Detailed Examination

 

Image Source birdinformer

*Heri Tarmizi

The interaction between migratory and resident birds in Southeast Asia presents both challenges and opportunities for conservation. 

Introduction

The Southeast Asian region is a biodiversity hotspot, home to a vast array of both migratory and resident bird species. These birds play crucial roles in maintaining ecosystem balance, but increased environmental stressors—such as habitat destruction, climate change, and human encroachment—have significantly altered the dynamics between migratory and resident bird populations. Specifically, the interaction between these two groups affects feeding patterns, prey availability, resting spaces, and overall biodiversity. This paper will explore the impacts of migratory birds on resident terrestrial birds in Southeast Asia, focusing on key aspects such as competition for food and habitat, changes in breeding cycles, and broader ecological implications.

Overview of Bird Migration in Southeast Asia

Southeast Asia lies on the East Asian-Australasian Flyway (EAAF), one of the world’s most crucial migratory routes for birds. This flyway connects the breeding grounds in Siberia and the Arctic with the wintering habitats in Southeast Asia, Australia, and New Zealand. It is home to some of the world's most diverse populations of migratory species, including shorebirds, songbirds, and raptors.

Every year, millions of migratory birds, such as the Yellow-breasted Bunting, Japanese Sparrowhawk, and several wader species, pass through Southeast Asia, utilizing its wetlands, forests, and coastal regions as stopover and wintering sites (Yong et al., 2015). These birds use these regions to rest and refuel before continuing their migration. However, these stopover areas are not isolated ecosystems but are also habitats for resident bird populations, leading to significant ecological interactions.

Competition for Resources: Feeding and Prey Dynamics

Migratory birds, with their high energy demands during long-distance flights, exert substantial pressure on food resources, directly competing with resident species. Studies in tropical Southeast Asian forests, such as those conducted in Malaysia, reveal that resident birds rely heavily on the same food sources, including insects, seeds, and small vertebrates, which are also the primary dietary staples of migratory birds during their stopovers (Yap et al., 2007).

In periods of migration, prey availability becomes a limiting factor, leading to competitive exclusion where the more aggressive or efficient feeders—often the migratory birds—gain an advantage over resident birds. The increase in bird density during migration can drastically deplete local food supplies, causing resident species to either shift their feeding times or locations, or in some cases, switch to alternative, less preferred prey. This phenomenon has been observed in Malaysia and Indonesia, where insectivorous resident birds often face reduced feeding success during the peak of the migratory season (Sodhi, 2002).

Further, in habitats like mangroves and coastal wetlands, where migratory shorebirds forage on benthic invertebrates, significant competition occurs for food resources such as crabs, worms, and small mollusks. This directly impacts local bird species like the Collared Kingfisher and several heron species, which also depend on these invertebrates for sustenance (Agoramoorthy & Pandiyan, 2016).

Impact on Habitat and Resting Sites

Migratory birds often use similar habitats as resident birds for resting and nesting, leading to direct competition for space. Forests, wetlands, and coastal areas, many of which are already degraded due to human activity, serve as critical rest areas for migratory species during their long flights. In places like the Mekong Delta, where wetland habitats are shrinking, migratory waterbirds increasingly crowd the remaining viable ecosystems, pushing resident birds further into suboptimal areas (Yong et al., 2021).

Inland forests, especially those that have been selectively logged, offer a unique case where competition for nesting sites becomes more pronounced. Studies in the tropical rainforests of Malaysia have shown that selective logging changes the structure of the forest canopy, making it harder for resident birds to find safe nesting spots. In these altered forests, both migratory and resident birds vie for the remaining available spaces, creating a scenario where nesting success rates for resident species can decrease (Yap et al., 2007).

Disruption of Breeding Cycles and Ecological Niches

The arrival of migratory birds can have a profound impact on the breeding cycles of resident birds, especially when the two groups share similar ecological niches. For instance, in the forests of Borneo and Sumatra, resident bird species such as the Crested Serpent Eagle and the Greater Racket-tailed Drongo experience disruptions in their breeding patterns due to increased competition for food and territory during the migratory season.

Research has shown that the breeding success of resident birds is often closely tied to the availability of food, which fluctuates due to competition with migratory species. When food resources are scarce, resident species are forced to delay breeding, resulting in a shorter breeding season and lower reproductive success (Yap et al., 2007).

Additionally, migratory birds may also affect the foraging behavior and habitat use of resident species, forcing them to shift their ecological niches. This shift can lead to long-term changes in the composition of bird communities in affected regions, with certain resident species declining in abundance due to increased competition and reduced access to essential resources.

Broader Ecological Implications

The ecological impacts of migratory birds on resident birds are not limited to direct competition for food and habitat. Migratory birds can also introduce new pathogens or parasites to resident bird populations, further complicating the survival of resident species. The spread of avian diseases, such as avian influenza, has been linked to migratory bird movements, posing significant risks to resident bird populations that may lack immunity to these diseases (Harrison et al., 2016).

Furthermore, the ecological roles played by migratory birds, such as seed dispersal and pest control, can sometimes overlap with those of resident birds. This overlap can either enhance or disrupt local ecosystems, depending on the balance between the two groups. For example, in agricultural areas, migratory birds may compete with resident species for insect prey, potentially reducing the effectiveness of resident birds as natural pest control agents. In contrast, the presence of migratory species can sometimes bolster local ecosystems by providing additional ecological services, such as the dispersal of seeds to new areas, which can benefit both resident birds and the broader ecosystem (Sodhi et al., 2010).

Conservation and Management Implications

Conserving both migratory and resident bird populations in Southeast Asia requires a multifaceted approach that addresses habitat loss, resource competition, and the impacts of human activity. Key to this is the protection of critical habitats, such as wetlands, forests, and coastal areas, which serve as vital stopover sites for migratory birds and breeding grounds for resident species.

Efforts to conserve migratory birds, such as the Ramsar Convention on Wetlands, have highlighted the importance of maintaining healthy ecosystems for the survival of both migratory and resident bird species. However, there is still much work to be done to ensure that conservation efforts are comprehensive and account for the complex interactions between these two groups. This includes the need for improved monitoring of bird populations, better enforcement of wildlife protection laws, and the development of sustainable land-use practices that reduce habitat degradation (Yong et al., 2021).

One innovative approach to conservation involves the use of citizen science, where birdwatchers and local communities play an active role in monitoring bird populations and reporting changes in species abundance and behavior. This approach has been particularly successful in Southeast Asia, where data on migratory bird movements is often scarce, and local knowledge is critical for identifying important stopover and breeding sites (Harris et al., 2013).

Conclusion

The interaction between migratory and resident birds in Southeast Asia presents both challenges and opportunities for conservation. While migratory birds bring valuable ecological services to the region, they also compete with resident species for critical resources, leading to potential conflicts. The key to maintaining healthy bird populations lies in preserving habitats, managing resources sustainably, and understanding the complex ecological dynamics at play. Through collaborative conservation efforts, it is possible to safeguard the future of both migratory and resident bird species in this diverse and ecologically important region.

References

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