Two years ago we shared the worrying news that the Bridled Quail-dove population had suffered a significant decline on St. Eustatius (Statia) following hurricanes Irma and Maria in 2017. Almost four years on, has the situation improved? It is time for an update.
Bridled Quail-dove in the Quill National Park (photo by Hannah Madden)
The Bridled Quail-dove (Geotrygon mystacea) is a shy, ground-dwelling species that is endemic to the Caribbean. It spends its day foraging the forest understory for fruits, seeds and the occasional gecko. Quail-doves prefer undisturbed forests with a closed canopy, and are sensitive to changes in their natural habitat. Unfortunately, the impacts of human-induced climate change mean hurricanes are becoming more intense and are occurring more often, which could spell trouble for this vulnerable species.
I began surveying Bridled Quail-doves in the Quill National Park in 2016. The Quill is a dormant volcano that rises to 600 meters with a large, accessible crater. It is the only habitat on Statia where the species occurs. Pre-hurricane, quail-doves were relatively common and observant birders could almost certainly spot one or two while hiking along the trails. The species breeds in May, when its mournful and unmistakable ‘whooo’ can be heard echoing through the forest.
Overgrazed understory in the Quill National Park, St. Eustatius (photo by Hannah Madden)
Hannah Madden during fieldwork in May 2021. Some 100 meter transects took up to 20 minutes to complete due to the steep and challenging environment (photo by Oliver Jones)
In September 2017 the forest habitat of the Quill suffered extensive damage from hurricanes Irma and Maria. Trees were stripped of leaves and fruits, branches were broken, and some trees did not survive. The effects of the hurricanes are still evident in some parts of the forest. In addition, we have a goat problem in the park; a very serious goat problem that has been pervasive for decades. Non-native, free-ranging goats overgraze already degraded habitats, resulting in a limited food supply and reduced understory cover for the quail-dove (as well as other forest-dependent species). Feral chickens disturb ground cover and compete for the same food source. Nest predators (invasive black rats and feral cats, both of which are present in the Quill) prey on eggs and chicks. This leads to lower reproduction and/or survival for the Bridled Quail-dove. There is no evidence of immigration of adults from nearby islands, which means populations are physically and genetically isolated. Based on the above we became concerned for the welfare of the Bridled Quail-dove and, thanks to support from many generous donors, BirdsCaribbean was able to provide funds to conduct post-hurricane surveys.
I conducted surveys of the Bridled Quail-dove in the Quill National Park. This involved walking previously established transects within the dove’s range (~150 to 600 m). We surveyed during peak breeding season (May) to allow for audio as well as visual detections. Once I saw or heard a quail-dove, I measured the distance of the bird from the center of the transect. I also recorded elevation and canopy height to assess their influence on Bridled Quail-dove presence. Once surveys were complete, I pooled all data from 2016 – 2021 to obtain abundance and density estimates per year.
As shown in the graph below, effort has increased from 1,200 m of transects in 2016 to over 15,000 m in 2021. This means survey effort has increased 13-fold to detect around one third of the number of doves that were counted in 2016. As you can imagine, repeating so many surveys is physically demanding.
Number of detections (left axis; red line) and survey effort (right axis; blue line) between 2016 and 2021 (no surveys were conducted in 2020).
Unfortunately, abundance estimates of the Bridled Quail-dove on St. Eustatius have declined significantly since 2016, and the current estimate is just 123 individuals (min 72 – max 210). This is less than 50% of the 2019 estimate, and less than 5% of the 2016 estimate.
After assessing the influence of covariates on Bridled Quail-dove presence, I found that doves were more likely to be present at higher elevations in habitats with a higher canopy (such as inside the crater, along the rim, and on the upper outer slopes of the Quill). In contrast, I found a strong negative effect of year on dove presence. This means that in the years following hurricanes Irma and Maria, doves were less and less likely to be present in the survey area.
What now for the Bridled Quail-dove on Statia?
We are extremely concerned about the Bridled Quail-dove on St. Eustatius. The combination of habitat degradation and predation by invasive species is likely responsible for the continued decline of this species. Its long-term survival is now uncertain unless urgent conservation actions are implemented. Even if the dove does persist, such a small and isolated population faces additional risks such as inbreeding. Since hurricanes are likely to increase in frequency and intensity, this could be catastrophic for the Statia population, and others in the region. Recently the International Union for the Conservation of Nature proposed that the Bridled Quail-dove be reassessed based on our work on Statia. This means the classification could be changed from Least Concern to Near Threatened or Vulnerable, but data are still lacking from many islands. We encourage enthusiastic birders to conduct their own surveys so that local populations can be assessed.
Passive acoustic monitoring device (source: www.wwf.org.uk)
We will be working with local conservation NGO St. Eustatius National Parks (STENAPA) to create an Action Plan for the Bridled Quail-dove. To effectively protect the species locally, it is likely that multiple conservation actions will be required: goat and cat removal, rodent control, and feral chicken removal from the park. In order to achieve this we need the support of the local government and the community. Because of the tremendous effort now required to monitor Bridled Quail-doves on Statia, we also suggest trialing passive acoustic monitoring (PAM) devices during the breeding season. This involves the placement of recording units that can be placed in the field for up to a month to record and interpret calls. Using these devices will allow us to collect data in less accessible areas, as well as increasing the scale of our study. Hopefully by combining conservation efforts with field surveys and PAM we will have better news in the coming years.
Hannah Madden is a terrestrial ecologist with the Caribbean Netherlands Science Institute, based on St. Eustatius. She is also a member of the IUCN Pigeon and Dove Specialist Group.
Article published in BioNews 47