Houston toad population supplementation in Texas, USA

Summary

The Houston toad, the first US amphibian listed under the Endangered Species Act in 1970, has continued declining across its east-central Texas range from habitat loss and prolonged drought, with field studies estimating juvenile survivorship as low as 0.03% to 1.5% and only one robust remaining subpopulation. Texas State University and the Houston Zoo began a renewed head-starting program in 2007, building on a largely unsuccessful 1980s effort that translocated nearly 500,000 captive-propagated individuals to a wildlife refuge, this time using genetic markers developed from recent dissertation research to track cohort survival despite the difficulty of physically tagging tiny released larvae. Collected egg strands are reared through metamorphosis at the zoo's amphibian quarantine facility, screened for parasites, disease and chytrid fungus, and released near dusk into the forest surrounding their source pond; releases grew from 500 toads in 2007, with 33.5% surviving to release, to 4,194 in 2009 and 14,728 in 2010, with captive survivorship improving to 50-55%. Genetic tracking and mark-recapture have detected head-started individuals months to years post-release at meaningfully higher frequencies than expected from natural survivorship, roughly 8% among near-adults versus about 0.1% among wild metamorphs. However, the team concludes the current small-scale annual effort, about six egg strands per year, meaningfully reduces mortality but cannot alone enable population recovery, and that far larger-scale intervention or captive propagation will be needed. The project rates itself Partially Successful, citing genuine juvenile survivorship gains and strong private-landowner engagement as the clearest wins so far.