Understanding ground-nesting habitat selection by waterbirds to prioritize invasive predator control on islands
The introduction of terrestrial carnivores to islands affects the conservation status of native prey, which are generally naïve to such predation pressure (David et al., 2017). For birds, the impact of predation is particularly strong during their reproduction, especially for ground-nesting birds (Amat & Masero, 2004). The cost of eradication programs in insular territories increases with the remoteness of the island (Martins et al., 2006), hence a more realistic management approach should prioritize conservation actions (Helmstedt et al., 2016). To achieve this, it is crucial to know where vulnerable birds nest, with detection probability being a key factor (Kery et al., 2009). On Navarino Island (2500 km2, 55°S) in southernmost Chile, where native terrestrial predators are lacking, the American mink (Neogale vison) has been present for over two decades now. Here, upland geese (Chloephaga picta) and flightless steamer ducks (Tachyeres pteneres) are two species vulnerable to mink nest predation (Schüttler et al., 2009). In a recent study, published in Basic and Applied Ecology (Gómez-Silva et al., 2024), we implemented a hierarchical occupancy model to reveal the preferred breeding habitats of these two ground-nesting waterbirds, aiming to prioritize areas for future mink control programs. We searched for nests from November 2021 to January 2022 along 80 transects (500 m each) on Navarino Island and 11 transects on ten nearby islets.
Valeria Gómez-Silva
Cape Horn University Center, University of Magallanes and Cape Horn International Center (CHIC), Puerto Williams, Chile
Foundation, Santa Cruz, Galapagos, Ecuador.
Simultaneously, we checked for mink presence on islets using ten camera traps (n = 385 trap nights). To provide predictive maps of nesting habitat preference, we classified a satellite image of the northern coast of Navarino Island using Google Earth Engine. Our results showed that islets are essential for breeding for both species (5.3 nests/km on islets vs. 0.8 nests/km on Navarino). The occupancy model supported this, particularly for flightless steamer ducks. Unfortunately, these islets were not predator-free, as all camera traps detected mink. This highlights that mink are able to swim in cold water up to 342.6 m from the coast of Navarino Island. We therefore suggest allocating resources for mink control during the breeding season on islets, as flightless steamer ducks seem to search for predator-free refugees. Additionally, our model indicated that upland geese preferred medium-dense shrubland, while flightless steamer ducks favored rocky coastlines. Nest detection was negatively affected by dense vegetation and, in the case of the upland geese, towards the end of the survey. Using these results, we generated a predictive map for the entire northern coast of Navarino Island, as a tool for conservation managers. Finally, our study contributes to the growing body of research indicating that studies monitoring nests should incorporate detection errors that may arise from the species’ characteristic nesting behavior.
References
Amat, J. A., & Masero, J. A. (2004). Predation risk on incubating adults constrains the choice of thermally favourable nest sites in a plover. Animal Behaviour, 67(2), 293–300. https://doi.org/10.1016/j.anbehav.2003.06.014
David, P., Thebault, E., Anneville, O., Duyck, P. F., Chapuis, E., & Loeuille, N. (2017). Impacts of invasive species on food webs: A review of empirical data. Advances in Ecological Research, 56, 1–60. https://doi.org/10.1016/bs.aecr.2016.10.001
Gómez-Silva, V., Crego, R. D., Jaksic, F. M., Flores-Brenner, G., & Schüttler, E. (2024). Understanding ground-nesting habitat selection by waterbirds to prioritize invasive predator control on islands. Basic and Applied Ecology, 78, 14–22. https://doi.org/10.1016/j.baae.2024.04.007
Helmstedt, K. J., Shaw, J. D., Bode, M., Terauds, A., Springer, K., Robinson, S. A., & Possingham, H. P. (2016). Prioritizing eradication actions on islands: It’s not all or nothing. Journal of Applied Ecology, 53(3), 733–741. https://doi.org/10.1111/1365- 2664.1259
Kéry, M., Dorazio, R. M., Soldaat, L., Van Strien, A., Zuiderwijk, A., & Royle, J. A. (2009). Trend estimation in populations with imperfect detection. Journal of Applied Ecology, 46(6), 1163–1172.
Martins, T. L. F., Brooke, M., de, L., Hilton, G. M., Farnsworth, S., Gould, J., & Pain, D. J. (2006). Costing eradications of alien mammals from islands. Animal Conservation, 9(4), 439–444.
Schüttler, E., Klenke, R., McGehee, S., Rozzi, R., & Jax, K. (2009). Vulnerability of ground-nesting waterbirds to predation by invasive American mink in the Cape Horn Biosphere Reserve, Chile. Biological Conservation, 142(7), 1450–1460.
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