D’Arros Island Sees Dramatic Growth in Shearwater Population

Significant Growth in Shearwater Population on D’Arros Island

Following the eradication of rats on D’Arros Island in Seychelles back in 2003, the island’s Wedge-tailed Shearwater population has experienced substantial growth. This remarkable ecological recovery was documented by researchers observing a dramatic increase in the number of breeding pairs over the years.

In 2016, researchers estimated around 2,768 breeding pairs of Wedge-tailed Shearwaters on the island. By 2021, although the number slightly decreased to 2,406 pairs, both figures represent an almost tenfold increase from the mere 254 pairs recorded in 2009. This significant rise suggests that the absence of rats has positively impacted the bird population, allowing them to thrive.

Area Expansion and Increased Nest Density

The study published in Marine Ornithology reveals more than just a numerical increase. The territory occupied by these seabirds had expanded from 3.40 hectares in 2016 to 3.85 hectares by 2021. Furthermore, the nesting patterns exhibited higher density, reinforcing the idea of a growing population. For instance, nesting densities per hectare varied, reaching as high as 2,391 nests in some areas by 2021.

What is particularly noteworthy is the discovery of new nesting areas that were previously unidentified. This expansion could be a direct effect of the eradication of rats, which previously posed a significant threat to the birds.

Innovative Methods in Population Estimation

To estimate these figures, researchers employed a mix of direct counts and area-based estimates. The latter was necessary in densely populated zones, where walking could disturb the closely spaced burrows. For accurate assessments, they utilized tools like burrow-scopes to examine deeper burrows, and also conducted call playbacks to verify burrow occupancy.

Despite variations in the methodologies compared to earlier surveys in 2009, the researchers are confident that the observed increase is genuine, reflecting the positive environmental changes following the rat removal.

Determining Key Breeding Periods

In addition to population counts, researchers also pinpointed November as the peak incubation time for these birds. Analysis of burrow occupancy showed a higher number of active incubations during November compared to October and December. This insight is expected to aid future studies in accurately comparing population changes over time.

The success story of D’Arros Island serves as a model for similar conservation efforts worldwide. The Wedge-tailed Shearwater population’s rebound underscores the critical impact that invasive species management can have on native wildlife, offering hope for ecosystems undergoing similar struggles.

Photo by Ignacio Amenábar on Unsplash