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Thesis Abstract – Higgins (2010)


An Assessment of the Potential Success of Translocation as a Conservation Strategy for Western Toads (Anaxyrus boreas) at the Robert J. Bernard Biological Field Station

Author and college:

Maya Higgins, Scripps College


April 23, 2010


Bachelor of Arts in Organismal Biology and Ecology


Marion Preest, Joint Science Department of Claremont McKenna, Pitzer, and Scripps Colleges


In response to imminent habitat destruction at the Robert I Bernard Biological Field Station (BFS), translocation was assessed as a conservation strategy for a population of Western toads (Anaxyrus boreas). Currently, the BFS is home to a relatively unstudied population of Western toads, which rely on the existence of a seasonal breeding pond in open land owned by Harvey Mudd College on the west side of the field station. Unfortunately, there are plans to develop this plot of land within the next few years and so the breeding pond will be destroyed. In an effort to protect the Western toads, which are listed as Near Threatened by the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species, a new breeding pond was developed within the protected portion of the field. station. Then, the potential of the new pond to be used as a habitat for Western toads was assessed. Pond temperatures, light intensities, algae growth, and suspended material were measured in both the original and the new ponds from January to April, 2010, and were found to be suitable in both locations for the development of Western toad tadpoles. When eggs were laid in the original breeding pond, egg and then later tadpole development were monitored in the field. Additionally, nearly 400 tadpoles were captured and raised in the laboratory in water from both the new and old ponds (as well as dechloraminated tap water) in order to determine how and to what degree the different pond water types affected the development and survival of the tadpoles. In the laboratory, tadpole survival and the percent of tadpoles to achieve frill metamorphosis was higher in water from the new pond than water from the original breeding pond, suggesting that there is nothing apparent about the water chemistry in the new pond that would limit tadpole development. Lastly, a mini-translocation of 400 young tadpoles was completed as a trial for a full-scale relocation attempt in the future. These tadpoles developed normally in the new pond when compared to tadpoles from the original pond and also had a high survival rate (at least 75%) to full metamorphosis. Translocation success cannot be determined without long term monitoring and unfortunately, although the aquatic habitat of the new pond seems suitable for relocation, the terrestrial habitat as well as the predator density surrounding the new pond may limit its success in the future. However, due to the lack of time before the original breeding pond is destroyed, fullscale translocation of eggs and tadpoles during the next breeding season is recommended.

Thesis availability:

Scholarship@Claremont – http://scholarship.claremont.edu/scripps_theses/137/

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