Mike is a PhD candidate in the Department of Geography at SUNY at Buffalo. He recently passed along the following synopsis of his 2011 field work:
In an effort to more thoroughly understand the spatial patterns of wood frog colonization of the hexagon pools, a mark-recapture study of both adults and metamorphs was undertaken. Beginning with the onset of breeding in April, adults were captured at the hexagon pools, as well as the ‘sugar shack’ pond, and marked using visible implant alpha (VIA) tags. These are small plastic tags that are injected subcutaneously so that the unique alphanumeric codes on them can be read through the frog’s skin. Sampling was done rather opportunistically, mostly by nocturnal dipnetting, with a small portion of captures coming from minnow traps. This opportunistic sampling was due to uncertainty about how wood frogs might colonize the hexagon landscape in the first year, and thus where to target, as well as the inability to get drift fences/pitfall traps in place ahead of time for structured sampling.
We were able to tag ~300 adult wood frogs in April 2011. Unfortunately, only 20% of those were from the hexagon pools, with the remainder being caught in the sugar shack pond. That pond has an enormous breeding population, as attested by the fact that two nights of sampling there (4 nights apart) yielded over 200 individuals with no recaptures. While the aim of the study is to focus on movement patterns within the hexagon region, a couple of factors motivated sampling in the sugar shack pond as well. First, the large population ensured a good sample of tagged individuals early on in the first field season when it was still uncertain how frogs would respond to the new hexagon pools. Second, it would be informative to see if any adults tagged in the sugar shack pond turn up as colonizers in the hexagons next year. This may be unlikely because the pond is over 600 meters away from the nearest hexagon pool, which is likely approaching the limit of adult dispersal distances, but even a small amount of evidence of this would be revealing. I am hopeful that a larger sample size in the hexagons can be achieved in spring 2012 with more dedicated effort there aided by pitfall trap arrays now in place at all of the 39 hexagon pools.
Indeed, the pitfall traps seemed to help quite a bit in capturing wood frog metamorphs in June/July. Sampling the hexagon pools over six nights with a total of 110 trap-nights produced VIA tagging of ~500 metamorphs. Again, the captures were spatially skewed, with 70% coming from hexagons 9 and 15 and 30% from six other hexagons. Hopefully this spatial pattern is not foreshadowing strong density-dependent mortality of these metamorphs, which has been documented before. Nevertheless, recaptures of these tagged metamorphs over the next two years should provide quality dispersal information. As metamorphs may often disperse over 1,000 meters, all hexagon pools are potential recapture locations.
Recapture data over the next two years will be limited by three primary factors: survival rates, capture probability, and tag loss/readability. Survival rates are out of my control, perhaps other than striving to sample spatially evenly to avoid effects of density-dependent mortality. Capture probability is a problem because my drift fences cover only ~20% of the pond perimeter. Additionally, tagged frogs may relocate to any number of the small natural vernal pools in the area, all of which are not able to be sampled. I am, however, hopeful that the traps now in place will increase my capture rates in the hexagon pools, but I am looking for advice on how to maximize capture probability this spring! I do not expect tag loss and readability to be too significant. VIA has been proven to be a successful technique for wood frogs and tag loss rates are quite low. So far I have recorded a handful of recaptures (all at their original pools) up to a week later, so I am at least confident that my tagging method is working. I have also double-tagged a sub-sample of the adults which should allow me to estimate tag loss by seeing how many double-tagged recaptures have just one tag remaining. Readability is a factor if the tag migrates underneath darker pigmented skin or flips upside down, which I have seen on occasion.
I’d like to thank ESF, especially Jim and Dr. Gibbs, for allowing me to join in on the Heiberg research and for the help they’ve given me. Also, thanks to Jim’s undergrad field assistants, Tom Maigret and Becca Landis, who helped me with lots of tagging. I’ll be looking for more help this spring and summer if anyone wants to get their hands dirty tagging wood frogs!
-Mike Habberfield, SUNY at Buffalo
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