Protecting Global Wanderers: The Role of the Convention on the Conservation of Migratory Species in Safeguarding Wildlife Habitats

Migratory species, often referred to as global wanderers, traverse vast distances across national boundaries, facing numerous threats to their survival, including habitat loss, climate change, and human-induced obstacles. These species, ranging from birds and marine mammals to terrestrial animals, rely on interconnected ecosystems for breeding, feeding, and resting. The conservation of their habitats is paramount to their survival, yet the transboundary nature of their journeys poses significant challenges to individual nations. Recognizing this, the international community has developed frameworks to protect these species and their habitats, with the Convention on the Conservation of Migratory Species of Wild Animals (CMS), also known as the Bonn Convention, serving as a cornerstone of global conservation efforts.

Adopted on 23 June 1979 in Bonn, Germany, and entering into force in 1983, the CMS provides a legal and cooperative framework for the conservation of migratory species and their habitats on a global scale. Administered under the United Nations Environment Programme (UNEP), the CMS facilitates collaboration among its 133 member states (as of recent data) to address the complex challenges faced by migratory species. This article explores the critical role of the CMS in safeguarding wildlife habitats, delving into its provisions, legal mechanisms for treaty adoption, and the implications for national and international conservation efforts. Additionally, it examines the legal frameworks surrounding treaty adoption, the monist versus dualist approaches to international law, and the relationship between the CMS and the Vienna Convention on the Law of Treaties (VCLT) of 1969.

The CMS is unique as the only global treaty specifically dedicated to the conservation of migratory species across terrestrial, aquatic, and avian environments. Its primary objective, as outlined in the preamble of the convention text, is to ensure the survival of migratory species by promoting international cooperation in the conservation of their habitats and addressing threats throughout their migratory ranges (CMS Convention Text, n.d.). The convention categorizes species into two appendices: Appendix I lists species that are endangered and require strict protection, while Appendix II includes species with an unfavorable conservation status that would benefit from international agreements for their conservation and management.

Key provisions of the CMS include obligations for Range States—countries through which migratory species travel, breed, or rest—to protect habitats, mitigate obstacles to migration, and collaborate on conservation measures. For species listed in Appendix I, Article III mandates Range States to prohibit the taking of these species, conserve and restore their habitats, prevent and minimize impediments to migration, and control factors endangering their populations (CMS Convention Text, n.d.). For Appendix II species, Article IV encourages Range States to conclude agreements for the conservation and management of these species, often through regional or bilateral instruments (CMS Convention Text, n.d.). These provisions underscore the CMS’s role as a facilitator of coordinated action to protect critical habitats across borders.

Beyond its legal obligations, the CMS fosters the development of daughter agreements and memoranda of understanding (MoUs) tailored to specific species or regions. Examples include the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) and the Agreement on the Conservation of Albatrosses and Petrels (ACAP). These instruments provide actionable frameworks for habitat protection, research, and monitoring, ensuring that the broader goals of the CMS are implemented at a practical level.

Habitat conservation is at the heart of the CMS’s mission, as migratory species depend on a network of ecosystems for their survival. The loss or degradation of these habitats—due to deforestation, urbanization, pollution, or climate change—can disrupt migration patterns and threaten population viability. The CMS addresses these challenges by mandating the protection and restoration of habitats under Article III(4)(a) for Appendix I species, which requires Range States to endeavor to “conserve and, where feasible and appropriate, restore those habitats of the species which are of importance in removing the species from danger of extinction” (CMS Convention Text, n.d.).

Additionally, the CMS emphasizes the importance of mitigating human-induced threats to habitats. Article III(4)(b) calls for Range States to “prevent, remove, compensate for or minimize, as appropriate, the adverse effects of activities or obstacles that seriously impede or prevent the migration of the species” (CMS Convention Text, n.d.). This provision is particularly relevant in addressing issues such as infrastructure development (e.g., wind turbines, roads, and dams) that can fragment migratory corridors or create fatal barriers for species like birds and bats.

The CMS also promotes the concept of ecological connectivity, recognizing that habitats are not isolated but form part of broader networks essential for migratory species. Through initiatives like the CMS COP (Conference of the Parties) resolutions, guidelines on ecological connectivity have been developed to encourage states to integrate habitat protection into national policies and land-use planning. For instance, Resolution 12.26 adopted at COP12 emphasizes the need for cross-sectoral cooperation to maintain and restore connectivity in landscapes and seascapes (UNEP, 2024).

Case studies further illustrate the CMS’s impact on habitat conservation. The protection of critical stopover sites for migratory birds under AEWA has led to the designation of wetland areas as internationally important under the Ramsar Convention, ensuring their safeguarding through collaborative management plans. Similarly, the CMS-led Central Asian Flyway initiative has facilitated cooperation among Range States to protect habitats for migratory birds traversing vast distances across Asia. These examples highlight how the CMS not only sets legal standards but also catalyzes on-the-ground action to protect wildlife habitats.

The CMS operates as an international treaty, and its adoption by states is governed by principles of international law, particularly those related to treaty-making capacity and consent. The convention text itself does not specify detailed procedural requirements for how states may enter into the treaty, as these are matters typically governed by a state’s domestic legal framework and international norms. However, Article XI of the CMS outlines the process for becoming a Party, stating that the convention is “open for signature by all States” and that it enters into force for a state upon ratification, acceptance, approval, or accession, following the deposit of the respective instrument with the Depositary (the Government of the Federal Republic of Germany) (CMS Convention Text, n.d.). This provision aligns with customary international law, which recognizes the sovereign right of states to enter into treaties as outlined in the Vienna Convention on the Law of Treaties (VCLT) of 1969.

Under Article XI(2), a state may sign the CMS and subsequently ratify it, or it may accede to the convention if it did not sign during the initial period. This flexibility allows states to join the CMS at different stages, ensuring broad participation. Moreover, Article XI(5) specifies that the convention enters into force for a state on the first day of the third month following the deposit of its instrument of ratification or accession, providing a clear timeline for legal commitment (CMS Convention Text, n.d.). These provisions ensure that states can engage with the CMS in accordance with their constitutional and legal processes for treaty adoption.

The CMS also encourages regional economic integration organizations to become Parties under Article XI(3), extending the scope of membership to entities such as the European Union. This provision reflects the convention’s commitment to inclusive cooperation, recognizing that regional bodies can play a significant role in coordinating habitat conservation efforts across multiple states.

The incorporation of international treaties such as the CMS into national law depends on a state’s approach to the relationship between international and domestic legal systems, which can be broadly categorized as monist or dualist. In a monist system, international law is automatically part of domestic law upon ratification of a treaty, without the need for additional legislation. In contrast, a dualist system views international and domestic law as separate, requiring specific domestic legislation to transform treaty obligations into enforceable national law.

For the purposes of this discussion, let us consider a hypothetical country, referred to as “State X,” to explore how the CMS might be adopted and implemented. If State X follows a monist approach, the CMS would become directly applicable in its legal system upon ratification under Article XI of the convention. This would mean that provisions such as those in Article III for habitat protection could be invoked directly in domestic courts, assuming the treaty is self-executing or contains directly applicable norms. However, many CMS provisions are framed as obligations of result rather than self-executing rules, often requiring states to adopt further measures for implementation, which could limit direct application even in a monist system.

Conversely, if State X adheres to a dualist approach, ratification of the CMS under Article XI would not automatically incorporate its provisions into national law. Instead, State X would need to enact specific legislation or amend existing laws to reflect obligations such as habitat conservation (Article III) and the development of regional agreements (Article IV). This process ensures that international commitments are aligned with domestic legal frameworks, but it may delay implementation due to legislative processes. In practice, many states, regardless of their monist or dualist orientation, often need to adopt implementing legislation or policies to give effect to CMS obligations, as the convention’s provisions are generally not detailed enough to be directly enforceable without adaptation to local contexts.

The choice between monist and dualist approaches also affects how treaties are translated into national law. In a dualist state like State X, translation might involve comprehensive environmental legislation that incorporates CMS goals into national wildlife protection laws, land-use planning regulations, and enforcement mechanisms. Public consultation, parliamentary approval, and alignment with existing laws would be critical steps in this process. In a monist state, while direct applicability may exist in theory, practical implementation often still requires regulatory frameworks to operationalize broad obligations like habitat restoration or migration barrier mitigation as stipulated in Article III(4)(b) (CMS Convention Text, n.d.).

Given that the CMS does not mandate a specific approach to implementation, it accommodates both monist and dualist systems, allowing states flexibility in how they meet their obligations. This adaptability is crucial for encouraging participation from countries with diverse legal traditions, ensuring that the convention’s habitat protection goals can be pursued globally despite varying national contexts.

The Vienna Convention on the Law of Treaties (VCLT) of 1969 is a foundational instrument in international law that codifies customary rules governing the formation, interpretation, and termination of treaties. While the CMS was adopted in 1979, after the VCLT’s entry into force in 1980, there is no explicit indication in the convention text or related documentation that the CMS is formally a “party” to the VCLT, as the VCLT applies to states and international organizations as parties to treaties, not to treaties themselves. However, the CMS, like other international treaties, is subject to the principles and norms of the VCLT, as these reflect customary international law widely accepted by the international community (OAS, 2011).

The VCLT provides critical guidance on treaty-making processes relevant to the CMS. For instance, Article 11 of the VCLT states that the consent of a state to be bound by a treaty may be expressed through signature, ratification, acceptance, approval, or accession—mirroring the mechanisms outlined in Article XI of the CMS (OAS, 2011; CMS Convention Text, n.d.). Similarly, VCLT Article 24 on the entry into force of treaties aligns with CMS Article XI(5), which specifies the timeline for the convention’s effect upon a state’s ratification or accession. These parallels demonstrate that the CMS operates within the broader legal framework established by the VCLT, ensuring consistency in how states enter into and are bound by its obligations.

For other countries considering joining the CMS, the VCLT offers a standardized legal basis for treaty engagement. The VCLT’s rules on treaty interpretation (Articles 31-33) can assist states in understanding CMS provisions, such as the scope of habitat conservation obligations under Article III, ensuring that commitments are clear and actionable. Furthermore, the VCLT’s provisions on reservations (Articles 19-23) are relevant, as CMS Article XIV allows states to enter reservations regarding specific species listed in the appendices, provided these do not undermine the convention’s overall objectives (CMS Convention Text, n.d.). This flexibility, underpinned by VCLT principles, enables states to tailor their participation while adhering to international legal norms.

The relationship between the CMS and the VCLT also informs best practices for treaty-making. States are encouraged to follow transparent and constitutionally grounded processes for ratification or accession, as outlined in VCLT Article 46, which addresses the validity of a state’s consent to be bound by a treaty. This ensures that commitments to the CMS are legally sound and politically sustainable, reducing the risk of non-compliance due to domestic legal challenges. Additionally, the VCLT’s emphasis on good faith (Article 26) reinforces the need for states to genuinely implement CMS obligations, such as habitat protection, rather than treating participation as a symbolic gesture.

While the CMS provides a robust framework for safeguarding wildlife habitats, its implementation faces several challenges. One significant obstacle is the varying capacity of states to fulfill their obligations. Developing countries, for instance, may lack the financial and technical resources to monitor migratory species, designate protected areas, or enforce habitat conservation measures as required under Article III. The CMS addresses this through capacity-building initiatives and partnerships with organizations like UNEP, but funding gaps and technical disparities remain.

Another challenge is the integration of CMS obligations into national policies amidst competing priorities. Habitat protection often conflicts with economic development goals, such as infrastructure projects or resource extraction. States must balance these interests, ensuring that commitments under Article III(4)(b) to mitigate impediments to migration are not sidelined by short-term economic gains. The CMS COP resolutions, such as those on sustainable development and ecological connectivity, offer guidance on achieving this balance, but implementation depends on political will and governance structures at the national level.

Despite these challenges, the CMS presents significant opportunities for advancing habitat conservation. The convention’s emphasis on international cooperation fosters knowledge sharing, joint research, and coordinated conservation strategies. Initiatives like the CMS Small Grants Programme support local projects aimed at protecting critical habitats, empowering communities to contribute to global conservation goals. Additionally, the CMS’s alignment with other multilateral environmental agreements, such as the Convention on Biological Diversity (CBD) and the Ramsar Convention, creates synergies that enhance habitat protection efforts across different frameworks.

The CMS has achieved notable successes in protecting migratory species and their habitats over the past four decades. The listing of critically endangered species in Appendix I has spurred targeted conservation actions, such as habitat restoration projects for the Siberian Crane and anti-poaching measures for the Saiga Antelope. The development of regional agreements under Article IV has also strengthened transboundary cooperation, as seen in the protection of marine turtle habitats under the Indian Ocean-South-East Asian Marine Turtle MoU.

However, the global decline of migratory species, as highlighted in the 2024 State of the World’s Migratory Species report, underscores the urgency of intensifying habitat protection efforts (UNEP, 2024). The report notes that habitat loss remains a leading threat, with over 70% of CMS-listed species affected by ecosystem degradation. This data emphasizes the need for states to prioritize CMS implementation, ensuring that legal commitments translate into tangible outcomes for wildlife habitats.

The CMS’s influence extends beyond its member states, as non-Parties often collaborate on specific initiatives or adopt similar conservation measures inspired by the convention. This ripple effect demonstrates the CMS’s role as a catalyst for global conservation norms, encouraging a collective responsibility to protect the interconnected ecosystems on which migratory species depend.

The Convention on the Conservation of Migratory Species of Wild Animals plays an indispensable role in safeguarding the habitats of global wanderers, addressing the complex challenges of conserving species that transcend national borders. Through its legal provisions, particularly under Articles III and IV, the CMS mandates habitat protection, mitigation of migration barriers, and international cooperation, providing a comprehensive framework for action. Its flexible approach to treaty adoption, as outlined in Article XI, accommodates diverse legal systems, whether monist or dualist, ensuring broad participation while allowing states to tailor implementation to national contexts.

The relationship between the CMS and the Vienna Convention on the Law of Treaties further strengthens its legal foundation, offering guidance on treaty-making and interpretation that informs how states engage with the convention. Despite challenges such as resource constraints and competing national priorities, the CMS presents significant opportunities for collaborative conservation, fostering initiatives that protect critical habitats and maintain ecological connectivity.

As the threats to migratory species intensify due to habitat loss and climate change, the CMS remains a vital tool for global conservation. By reinforcing commitments to habitat protection and encouraging adherence to international legal norms, the convention not only safeguards wildlife but also preserves the ecological balance of our planet for future generations. States must continue to strengthen their engagement with the CMS, ensuring that legal obligations translate into effective, on-the-ground action to protect the world’s migratory species and their habitats.

• CMS Convention Text. (n.d.). Convention on the Conservation of Migratory Species of Wild Animals. Retrieved from https://www.cms.int/en/convention-text
• OAS. (2011). Vienna Convention on the Law of Treaties 1969. Retrieved from https://www.oas.org/legal/english/docs/Vienna%20Convention%20Treaties.htm
• UNEP. (2024). Landmark UN Report: The World’s Migratory Species of Animals Are in Decline, and the Global Extinction Risk Is Increasing. Retrieved from https://www.unep.org/news-and-stories/press-release/landmark-un-report-worlds-migratory-species-animals-are-decline-and