Final Summary: Drawing Conclusions

It is hard to believe the summer is already over – it seems like just yesterday I was tagging my first toad! Field work has its challenges (mosquitos, bad weather, MUD) but overall I have found the experience to by highly rewarding. I have enjoyed getting to be outside all day studying species that fascinate me, and I am proud of the massive data set we have amassed over the past three months. And now, finally, the time has come to draw conclusions from all of this summer’s hard work!

One of the objectives I had this summer was to assess harmonic direction finding’s viability as a tagging method. We used this method on two species of toads, tree frogs, and aquatic frogs this summer with varying success. The biggest challenge was not, as I suspected early on, detecting frogs beneath log cover, but actually loss of transponders due to water. We rarely were able to follow aquatic frogs for more than a few days because they could swim out of their transponder harnesses fairly easily. Those that we did follow for long periods generally remained in terrestrial environments. So for this reason, I would not recommend harmonic direction finding for use on aquatic species.

However, both toads and tree frogs seemed to respond well to this method. Though Cope’s gray tree frogs lost their transponders frequently, we have been able to consistently follow green tree frogs for very long periods. The biggest challenge when dealing with tree frogs is usually just accessing their locations, as they usually are in extremely swampy areas. Additionally, some tree frogs that were followed for extended periods would begin to get abrasions from their transponder and need to have it removed, so monitoring the overall condition of individuals has proven to be very important. Toads also responded extremely well, as they rarely lost their transponders and we have not yet documented any cases of abrasions. Furthermore, logs and even burrows did not prove to be a major hindrance to detecting species, as we were able to find buried and well-hidden toads, though this did sometimes require extensive searching of the landscape. For these reasons, I believe harmonic direction finding is a viable method for use on certain terrestrial anuran species, particularly tough-skinned species such as toads.

The primary objective of this study has always been to quantify movement and microhabitat however, and I am pleased to present the results of this summer! I have only analyzed data for three species: American Toads, Fowler’s Toads, and Green Tree Frogs, as these are the species for which I had the highest sample size.

Average Daily Movement

American Toad: 5.3 m     Fowler’s Toad: 6.3 m     Green Tree Frog: 3.6 m

humidity and movement chart

 

american toad

fowlers

gntf

Average daily movement proved to be fairly similar between the toad species, despite the fact that one was in the breeding season and the other was not. This may indicate that Fowler’s Toads, which breed in the summer, are not tied to breeding ponds as would typically be expected. Green Tree Frogs, however, moved much less than either toad species, likely as a result of their strong fidelity to ponds during the breeding season. As a continuation of this research, I will continue to monitor all species throughout the fall to see if there is a change in distances moved between the breeding and non-breeding seasons.

I ran a Pearson Correlation to see if temperature, humidity, or soil moisture had an impact on distances moved for each species. While most of these results were not statistically significant, humidity was strongly correlated with average daily movement in american toads (p-value = 0.002). Though there was a great degree of individual variation between toads, individuals consistently moved longer distances when it was more humid out. This solidifies the idea that moisture is extremely important to anurans, particularly terrestrial species like toads that are more at risk of desiccation because they reside farther from water sources. The wider range of movement distances between individuals also demonstrates that toads are highly variable, and each toad likely adapts its own specific survival strategies depending on its environment.

Another interesting finding was that while American Toads are almost always associated with leaf litter, the closely related Fowler’s toads seems to utilize a wider range of microhabitats. However, again, individual preferences are not something that can be ignored here. While this data is an aggregate, it is worth noting that individual toads usually stuck with one type of microhabitat. In other words, one toad might always be found in vegetation, but another toad of the same species in the same area might always be found in leaf litter. In short, toads are developing unique strategies to survive. This may be due to differences in foraging ability, camouflage capability, or specific physical characteristics. In any case, it demonstrates how flexible toad species are and hints at why they have had such a large range.

Green Tree Frogs seemed to be highly arboreal, and were rarely found on the ground, as was expected. The fact that they were usually found in the middle or end of tree branches may indicate that they prefer these areas for camouflage purposes, as these areas are generally more leafy and green than the tree trunk.

Overall, this data provides a better picture of where and how far these species are moving during the warm months of the year, and, for some of them, during their breeding season. I plan to continue to follow these species through the fall to look for any changes in movement or microhabitat as the breeding season comes to a close. One green tree frog may have already begun migrating, as he was found 30m from the water’s edge a few days ago! I will also analyze the vegetation, canopy, and understory data that we collected this summer and see how preferences may differ between species.

This has been a whirlwind of a summer, and I am so excited to come out of it with significant results! This is the first step in better understanding how and why anurans move through landscapes, and can’t wait to continue my work through the fall!

-Courtney

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