Kevin Verdel
ST. EUSTATIUS–Caribbean Netherlands Science Institute’s (CNSI’s) Science Café featured Master-degree student from Utrecht University Kevin Verdel, who gave a presentation about the impact of rodent control on the nesting success of red-billed tropicbirds.
Verdel spent eight months on Statia assisting CNSI with the biodiversity component of an ongoing rodent-control project, funded by the Ministry of Economic Affairs.
Pilot/Signal Hill was chosen for rodenticide treatment due to its importance as a nesting site for tropicbirds. Before treatment started, the site was assessed for rodent density using tracking tunnels.
Baited ink cards were placed in tunnels to identify the prints of animal visitors lured to the card. Data from the tracking tunnels revealed a significant population of black rats in the area.
Once treatment began, however, rodent density dropped to zero and has remained so thanks to ongoing checks and replenishment of the bait stations.
CNSI researchers hoped that a reduction in the rat population would lead to an increase in tropicbird nesting success. Unfortunately, the results from the 2017-2018 breeding season revealed a slight decline in reproductive success, the cause of which is not yet known but may in part be linked to an increase in land crabs, since rats also prey on young land crabs.
Crabs, which are not susceptible to most anticoagulant rodenticides, readily consume bait and can interfere with bait stations.
Rodenticide can persist in crab tissue for at least 56 days and present a secondary exposure pathway for other animals, including humans.
CNSI will test “essence” compounds such as cinnamon, nutmeg, orange, or lemon as crab deterrents when implementing treatment in the future.
Other – yet undetermined – factors that may have affected tropicbird productivity away from the nesting site could be related to foraging, sea surface temperature, and/or weather anomalies, such as El Niño/La Niña and hurricanes.
The results of this study are in line with previous years, whereby tropicbird nests were more likely to fail during the incubation stage compared with the chick stage. This was confirmed through camera trap images, which documented a rat and a land crab feeding on unattended eggs. The study will continue until September 2019.
CNSI and Verdel are grateful to NuStar Energy NV for allowing access to the site, and to Bell Laboratories, Inc. for its generous donation of “Ambush” bait stations and “Final All-weather Blox.”
Source: The Daily Herald https://www.thedailyherald.sx/islands/78591-rodent-control-fails-to-impact-nesting-success-of-tropicbirds
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