Associations Between Land-Use and Land-Cover Change and Waterbird Community Structure in a Coastal Ramsar Wetland, Ghana
This study integrates Sentinel-2 remote sensing and waterbird census data to demonstrate that variations in land-use and land-cover composition at Ghana's Densu Delta Ramsar Site are positively associated with specific waterbird community structures, highlighting the value of combining satellite-derived environmental data with biodiversity monitoring for wetland management.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Wetlands are among the most productive places on Earth, acting as nature's sponges and filters. They clean water, control floods, and store carbon, but perhaps most visibly, they serve as vital rest stops and dining halls for birds that travel thousands of miles between their breeding grounds and winter homes. These birds, known as waterbirds, are sensitive to their surroundings; if the water gets too deep, the mud dries up, or the plants disappear, the birds simply move elsewhere. Because their presence and numbers change so quickly in response to the environment, scientists often look at them to understand the health of a wetland. However, watching a wetland change over time is difficult. The landscape shifts with the seasons, and human activity constantly reshapes the edges where land meets water. To see the full picture, researchers need a way to watch the land itself change while simultaneously counting the birds that rely on it.
In the coastal region of Ghana, near the capital city of Accra, lies the Densu Delta, a wetland designated as a site of international importance. This area is a mosaic of lagoons, mudflats, and marshes, but it is also surrounded by a rapidly growing city. As the city expands, the land changes, and scientists wanted to know how these changes affect the birds. A team of researchers set out to connect the dots between the shifting landscape and the waterbird community. They combined two different types of information: satellite images that showed how the land was being used, and annual counts of the birds that visit the site. By looking at the same place over a few years, they hoped to see if specific types of habitat changes were linked to changes in the number or types of birds present.
The researchers used satellite images from the European Space Agency to map the Densu Delta. They sorted the landscape into four main categories: open water, wetland vegetation like reeds and mangroves, areas used for farming or degraded land, and built-up areas like roads and buildings. They found that built-up land and bare soil already covered a large portion of the site, particularly in the western and central parts, while open water remained concentrated in the southern lagoons. The vegetation formed a thin, sometimes broken, belt around the edges of the water. To ensure their maps were accurate, they checked their work against known ground features, finding that their classification was highly reliable.
At the same time, the team examined records from the International Waterbird Census, which counts the birds at the site every January. Between 2020 and 2023, they identified 62 different species of waterbirds. The total number of birds fluctuated significantly from year to year. In 2021, the census recorded the highest number, with nearly 29,334 individuals, while 2020 and 2023 saw much lower counts, around 15,000 to 16,000. The variety of species also changed, peaking in 2021 with 50 species and dropping to 41 in 2023. Throughout these years, the most common birds were shorebirds—species that feed on the exposed mud and shallow water—followed by birds that eat fish and those that feed on open water.
When the researchers compared the land maps with the bird counts, they found some clear patterns. The number of wading birds, such as herons and egrets that hunt in shallow water among plants, was strongly linked to the amount of wetland vegetation. When there was more vegetation, there were more of these birds. Similarly, birds that eat fish and those that are true waterfowl showed a moderate connection to the amount of open water available. However, the relationship was not the same for all groups. The number of shorebirds did not seem to depend heavily on the amount of degraded or agricultural land, suggesting that other factors, like the tides or the availability of small creatures to eat, might be more important for them.
The study highlights that while the Densu Delta faces pressure from urban expansion and land conversion, it remains a critical hub for migratory birds. The findings suggest that keeping the vegetated parts of the wetland intact is likely the most important step for supporting the birds that rely on those specific habitats. The researchers noted that because they only had four years of data, these connections are best viewed as strong hints rather than absolute proof. Nevertheless, the work demonstrates that combining satellite views of the land with traditional bird counts offers a powerful way to monitor how coastal wetlands are faring. It provides a clearer picture of how the physical changes to a landscape ripple through the ecosystem to affect the wildlife that calls it home.
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