Testing Photogrammetry in Assessing Health of Houston Toads (Bufo [=Anaxyrus] houstonensis)

Abstract

The Houston toad (Bufo [=Anaxyrus] houstonensis) is an endangered amphibian species that occupies a small range in Texas, USA. Despite recent increases in juvenile detections, obtaining data is limited by a narrow temporal window of juvenile emergence. This necessitates the rapid collection of ecological data. Because of this, we seek to test the quality of image-based measurements as an alternative to assessing the body condition of Houston toads. We used caliper- and image-based measurements of wild-caught adult toads and captive-bred juveniles, while recording handling time for each method with the juveniles. We compared scaled mass indices (SMI) and residuals from ordinary least squares regressions (OLS) between methods and life stages. Handling time of juvenile toads was significantly lower (p < 0.0001) for the image-based trial than the caliper-based trial. While SMI values violated key assumptions for a valid Condition index (CI), OLS condition index values did not. OLS condition values from the image-based trial were also not statistically significantly different to those from the caliper-based trial. These observations suggest that our image-based measurement technique is a valuable alternative to gaining morphometric data, and that applying this data to an OLS residual index is a more appropriate approach to monitoring individual- and population-level health in Houston toads.

Keywords

Photogrammetry / Houston toads / Body condition / Endangered species / Conservation / Juveniles

Supplementary Materials

The following supporting information can be found at: https://www.sciepublish.com/article/pii/583, Figure S1:Plot representing correlation of scaled mass index (SMI) values and snout urostyle length (SUL) in juvenile Houston toads (Bufo [=Anaxyrus] houstonensis); Figure S2: Plot representing correlation of scaled mass index (SMI) values and snout urostyle length (SUL) in adult Houston toads (Bufo [=Anaxyrus] houstonensis ); Figure S3: Plot representing correlation of residual condition indices and snout urostyle length (SUL) in juvenile Houston toads (Bufo [=Anaxyrus] houstonensis); Figure S4: Plot representing correlation of residual condition indices and snout urostyle length (SUL) in adult Houston toads (Bufo [=Anaxyrus] houstonensis.

Acknowledgments

We thank the United States Fish and Wildlife Service, Texas Department of Transportation, Texas State University,Houston Zoo Inc., Fort Worth Zoo, and Dallas Zoo for their collaborative efforts in enabling recovery measures for Houston toads. We would also like to thank Ferris Zughaiyir, Jim Bell, and DJ Stout for their assistance with and facilitation of field work. Finally, we thank Saunders Drukker for analytical tips.

Author Contributions

Conceptualization, M.R.J.F., S.S., and J.M, Data Collection, S.S. and J.M., Data Analysis, S.S. and A.F., Data Curation, S.S. and J.M., Writing—Original Draft Preparation, A.F., Writing—Review & Editing, A.F., S.S., M.R.J.F., and J.M., Visualization, S.S., Supervision, M.R.J.F., Project Administration, M.R.J.F., Funding Acquisition, M.R.J.F. All authors have read and agreed to publish the manuscript.

Ethics Statement

Sample collection from toads was authorized under a USFWS permit (TE039544-0) and a TPWD scientific research permit (SPR-0102-191). Our experimental protocol was approved on 10 September 2024 by the Texas State University Institutional Animal Care and Use Committee (Approval number: 35141129; Protocol number: 9698). We adhered to the Animals in Research: Reporting On Wildlife (ARROW) guidelines by taking all measures to mitigate stress.

Informed Consent Statement

Not Applicable.

Data Availability Statement

R scripts used in analyses will be made available by the corresponding author upon reasonable request.

Funding

This research was funded by United States Fish and Wildlife Service as well as Texas Department of Transportation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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