Migratory species are animals that move cyclically and predictably across large distances, often crossing international boundaries, to find food, mates, and suitable habitats for different phases of their annual life cycle. This immense mobility is the fundamental reason why their conservation presents unique difficulties compared to sedentary species. Since these animals rely on a network of locations rather than a single, fixed habitat, protecting them requires coordinated effort across vast geographic scales and multiple political jurisdictions. The challenges are rooted in the complex interplay of international law, ecological necessity, and the cumulative impact of threats encountered along their journey.
The Challenge of Transboundary Governance
The long-distance travel of migratory species means they routinely cross the borders of multiple nations, states, or other political entities. No single government has the authority to protect the species across its entire range. Protection relies instead on a fragmented patchwork of national laws, varying enforcement capabilities, and sometimes conflicting national priorities.
International agreements, such as the Convention on the Conservation of Migratory Species of Wild Animals (CMS), exist to promote cooperation. However, their effectiveness depends on the willingness and capacity of member nations to implement necessary protections. For example, many countries along the East Asian-Australasian Flyway have not ratified the CMS, creating legal gaps where conservation efforts cannot be universally applied. The lack of a unified legal framework means a species protected in its breeding grounds may face no safeguards against habitat destruction or overexploitation in stopover locations.
Differing governance regimes mean that conservation standards are inconsistent across the species’ range. A country with robust environmental laws may share a migratory path with a nation where economic development takes precedence, resulting in the destruction of essential habitats. This geopolitical complexity requires sustained diplomatic efforts and shared resource allocation, which is often slow and difficult to maintain.
Protecting the Full Life Cycle Habitat
Migratory species require a sequence of distinct, connected habitats—including breeding sites, non-breeding areas, and multiple stopover points—to complete their full annual cycle. Protecting only the breeding or wintering grounds is insufficient because the successful journey depends on the health of every location along the migratory corridor. The failure to protect even one critical point can lead to the collapse of the entire population.
Intermediate stopover sites, often called bottleneck points, are where large numbers of animals congregate to rest and refuel before the next leg of their journey. If these sites are degraded or destroyed, migrants may lack the energy reserves needed to survive the rest of the migration, which often has a higher mortality rate than stable breeding or wintering periods. For example, the rapid loss of intertidal mudflats in the Yellow Sea has been a major factor in the steep decline of shorebirds along the East Asian-Australasian Flyway, as these are indispensable refueling stations.
Effective conservation must focus on maintaining habitat connectivity across continents and oceans, ensuring an unimpeded movement pathway. A global review found that only about 9% of migratory species had adequate habitat protection across their entire range, highlighting a systemic failure to manage these disparate locations as a single ecological unit. Furthermore, poor habitat quality during winter can negatively affect reproductive success in the following breeding season thousands of miles away.
Disparate and Compounding Threats
Migratory species face a unique challenge because threats are not uniform across their range but are geographically specific, accumulating along the entire migration route. A species may encounter habitat loss from agricultural expansion on its breeding grounds, face illegal hunting at a stopover site, and then suffer incidental capture from fishing gear (bycatch) in its wintering waters. The cumulative impact of these varied threats makes mitigation complex, as no single conservation action can address all dangers simultaneously.
The two greatest drivers of decline for migratory species are habitat loss and overexploitation, affecting three out of four and seven out of ten CMS-listed species, respectively. Habitat fragmentation from infrastructure like roads and dams acts as a physical barrier, blocking traditional migratory paths for land mammals and freshwater fish like the Russian sturgeon. Overexploitation includes unsustainable activities like overfishing, which has caused populations of migratory fish, such as sharks and rays, to decline by an average of 71% since 1970.
Climate change acts as an amplifier, complicating the threat landscape by altering the timing and location of necessary resources. Changing temperatures can cause a mismatch, where migrants arrive at a location when their food source is no longer available. For example, higher temperatures can skew the sex ratio of sea turtles or reduce the foraging time for African wild dogs, directly impacting population viability.
Scientific and Logistical Monitoring Gaps
The sheer scale of movement in migratory populations creates immense practical difficulties in tracking and studying them effectively. Scientists need data on migration routes, timing, and population size across vast, often remote, and sometimes politically sensitive regions. Gaining this information is costly and logistically demanding, leading to data gaps that hinder the design of effective protected areas.
Tracking devices like satellite telemetry are expensive, and their size and weight limit their use primarily to larger animals, leaving smaller species like many songbirds poorly understood. For these smaller birds, high-tech tools like weather radar and passive telemetry systems (e.g., Motus) are emerging solutions, but they require extensive, synchronized infrastructure across multiple countries. Accurately assessing population sizes is also challenging, as censuses must be coordinated across different jurisdictions that may have limited scientific capacity.
The result is a lack of conservation-relevant information, particularly regarding specific stopover sites and the precise mortality drivers along the route. Without synchronized data collection and information sharing across international borders, it is nearly impossible to quantify the impact of geographically variable threats or identify the most effective allocation of limited conservation resources. This knowledge gap means conservation efforts often lag behind the rapid pace of environmental change and habitat loss.