Seasonal and Ontogenetic Changes in the Sex Ratio of a Population of Stinkpots (Kinosternidae: Sternotherus odoratus)




Swannack, Todd M.

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Current hypotheses suggest turtle populations with biased sex ratios are the result of sampling errors such as improper sex determination, trapping bias, and behavioral differences between the sexes. This study was undertaken to determine if the observed sex ratio of a population of stinkpots (Sternotherus odoratus) was an artifact of sampling biases. A total of 989 (637 males, 352 females) individual stinkpots were captured from 1996 through 2000 at Spring Lake, Hays County, Texas. The overall sex ratio based on all census techniques was significantly male biased (1.8:1; p < 0.001). The sex ratio changed across size classes from a male bias in the smaller classes to a balanced ratio in the largest size classes. Both hoop traps and dip nets used to sample the population produced male biased sex ratios (p < 0.001). Hoop traps were baited with a chicken neck or a mature female stinkpot bimonthly from May 1999 - May 2000 to determine if the biased sex ratio was due to mate searching behaviors by males. The sex ratio deviated from 1:1 during November (p < 0.05) when only 5 males were captured and January (p < 0.001) when an excess of males entered the trap baited with the female. The sex ratio for the entire year for each trap type did not deviate from 1:1. The experimental trapping reinforced the view that the sex ratio in this population is inherently biased and is not an artifact of sampling techniques.



Kinosternidae, stinkpots, turtles, sex ratio, sampling


Swannack, T. M. (2000). Seasonal and ontogenetic changes in the sex ratio of a population of stinkpots (kinosternidae: Sternotherus odoratus) (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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