Mike Habberfield's 2011 field season report

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

2011 Field season review

More than five months have passed since my last posting suggested that the Heiberg amphibians were taking a liking to the newly constructed pools. Much has happened since then, both in terms of the ecological development of the pools and in our efforts to monitor them. I will attempt now to share the most significant happenings.

Egg mass surveys
In the previous blog post, I noted that colonization of newly constructed pools appeared to be successful, but wondered if that would come at the expense of reproductive investment in pre-existing pools. This did not turn out to be the case: wood frog and spotted salamader egg mass counts in pre-existing pools were comparable or in many cases greater in 2011 than in 2009 or 2010.

In the Microarray, 87 wood frog egg masses were deposited in 15 of 32 (47%) pools, and 100 spotted salamander egg masses were deposited in 12 pools (38%). Although most pools contained water in the early spring, both species demonstrated remarkable avoidance of pools that dried rapidly and offered no chance for successful larval development.

In the Hexagon Array, 158 wood frog egg masses were deposited in 29 of 39 (74%) pools, and 135 spotted salamander egg masses were deposited in 22 pools (56%). As described in the previous post, frogs colonized new pools more readily than salamanders. Interestingly, niether species avoided pools with green frog tadpoles that had successfully overwintered. More on this later...

Leaf litter decomposition experiment
In mid-May, I tied to a stake at the deepest point of each pool three onion bags, each containing a known mass (approximately 3 g) of red maple leaves collected during autumn of 2010. These were retrieved in late July, and I am in the process of taking final weights to determine decomposition rates for each pool.

Macroinvertebrate sampling
I conducted two rounds of aquatic macroinvertebrate sampling with nocturnal light traps developed by Professor Bruce Smith, the first in mid-May and the second in late June/early July. All Hexagon Array pools contained water and were trapped during both survey periods, but only 18 and 10 Microarry pools were inundated and trapped for the first and second surveys, respectively. Samples have been preserved and are waiting for the snow to fly and the pools to freeze before they will get the attention they deserve.



SUNY Buffalo PhD student Mike Habberfield deploys an aquatic light trap.

 Amphibian larval sampling
I had planned to conduct two rounds of sampling wood frog and spotted salamander larvae so as to measure population trends and individual growth rates. However, during the first survey period during the last week of May and the first week of June, salamanders had only begun emerging from eggs. During the second survey period (mid- to late June), salamanders had hatched, but wood frog tadpoles were dangerously close to being fully developed. Thus, a third round was conducted in mid-July so that two surveys were conducted between the period when the last embryo has hatched and the first individual has metamorphosed for each species.

Aside from additional work imposed by the different developmental schedules of wood frogs and spotted salamanders, by and large, the pipe sampling technique worked very well. We generally worked out a routine in which helpers would do the pipe sampling and bring me their quarry in numbered bins. I identified the animals, weighed amphibian larvae, and preserved a sample (n<30) of tadpoles for developmental staging in the lab since it was impractical to reliably stage tadpoles in the field.



SUNY ESF PhD student Jim Arrigoni plunges a pipe sampler into the water column to trap and sample amphibian larvae.

 


Field technician Tess Youker delivers pipe samples to Jim Arrigoni, who is hiding from the rain and wind in the F150 mobile lab.



Larval wood frogs and spotted salamanders captured with pipe sampler.

 Although I have only begun to assimilate this summer's data, a few interesting patterns were obvious on the ground. First, and no big surprise here, temperature had a huge influence on developmental rates. The pools in the field part of the Microarray drove our sampling schedule - the animals in these unshaded pools were the first to hatch and metamorphose. Second, density of wood frog tadpoles appeared to exert a strong inverse effect on developmental rates. Two adjacent pools that appeared identical in most respects had very different wood frog developmental rates when one had had substantially more egg masses deposited in it. (The lesson: more might not be better from a recruitment or fitness perspective). Third, wood frog tadpoles generally coexisted well with overwintered green frog tadpoles in the pools where the two species were sympatric. I noticed that the green frog tadpoles generally occupied the benthos in the shallow zone, whereas wood frog tadpoles tended to be more pelagic (we stratified pipe sampling accordingly). However, in two pools, green frog tadpoles consumed all of the wood frog embryos. Why this happened in only two pools (out of 10 in which they two species coexisted) is an open question. Finally, in two pools in the Hexagon Array, wood frog tadpole die-offs in late June suggested Ranavirus infections. This has subsequently been confirmed with PCR analysis by field technician Tess Youker with the help of Brooke Reeve, a recent MS graduate of SUNY ESF.

Hydrological monitoring
With help from spring semester interns Nathan Heath, Becca Landis and Tom Maigret, we created and installed guages to measure water levels in each pool. Water levels have been recorded at least every 10 days since installation following ice out.


Surface and substrate temperature monitoring apparatus (left) and water level gauge (right).

 Here is a hydrograph example from Microarray Pool 1:

This pattern was typical in many of the pools in the Hexagon Array: water levels lowered during summer, but like last summer, very few of the Hexagon Array pools dried completely. On the other hand, many of the pools in the Microarray dried prematurely. This situation will give perspective on the consequences of failure to replicate vernal pool hydrology on both ends of the hydroperiod gradient.

Temperature monitoring
Thermochron iButtons were deployed at the water surface and at the substrate in all pools in mid-November 2010, and recovered and replaced in late July 2011. Unfortunately, a large number of the units were corrupted, and I am uncertain whether this was due to exposure to harsh winter conditions or because I only double-coated units with Plasti-Dip, as opposed to triple-coating units that were deployed during the spring-to-autumn period of 2010, when zero failures occurred. Data from Hexagon 20 Pool E are shown below. Note the thermal inversions apparent in late November and mid-April.

Other happenings
With the support of an Edna Bailey Sussman Foundation internship, I sampled larval amphibians and macroinvertebrates in nine pools in southern NY on the property of Jim Curatolo of the Upper Susquehanna Coalition. Three pools were of natural origin, two were built in 2006, and four in 2008. The intent of this side-project was to assess development of invertebrate communities and production of amphibians at greater time scale than is permitted in the Heiberg pools, which were all constructed during 2010.

Shortcomings
Despite the successes described above, I was unable to deploy tiles for sampling periphyton. Although this certainly would have yielded interesting data in and of itself as well as in comparison to other biological data, it simply was not possible to undertake this component of the study along with the damands of other components.

Thanks!
I was fortunate this summer to have the help of three diligent, humorous and hardy people. Tess Youker of ESF was out at Heiberg more than anyone, and allowed me to frantically worry about many fewer things. As part-time interns, Shelby Persons of SUNY Cortland and Ryan Doherty of ESF did not feed quite as many mosquitos and deer flies as Tess, but their contributions of labor and cheer nonetheless are greatly appreciated.


Field technician Tess Youker steps carefully through the forest at night, intern Shelby Persons delivers more samples of larval amphibians, and intern Ryan Doherty admires his afternoon's work of waterproofing Thermochron iButtons

 -Jim Arrigoni, SUNY-ESF

Easter egg hunt

When I was a child, it was an annual family tradition to participate in an Easter egg hunt in my aunt and uncle's back yard, where dyed eggs were stashed among the landscaping. It's been more than 20 years since my sisters and cousins and I competed for chocolate prizes, and I have rarely rekindled those fond memories, until today when ESF con bio undergrad Tom Maigret and I undertook egg mass surveys among the newly constructed Heiberg pools. I am amazed and ecstatic at what we found.

Before I report our numbers, let me confess that I have maintained a worry about the vulnerability of my dissertation research to the cooperation of animals that we know exist in decent numbers across the landscape, but may be fickle by taking a year off from reproductive activities if the weather is uncooperative (which there were suggestions might be the case with this late and, at times, dry spring), or by entirely ignoring the newly constructed pools, instead preferring their pre-existing oviposition sites. My worry is gone.

Recall that within the pre-existing ponds within the 24-hexagon landscape, 60 wood frog egg masses were observed in both 2009 and 2010. In contrast, 4 spotted salamander egg masses were observed in 2009, and 165 masses in 2010. I have not yet surveyed these pre-existing habitats, but among the 39 constructed pools we counted 131 wood frog and 34 spotted salamander egg masses! There are masses in all hexagons except for the single pool in Hexagon 14, and nine pools lacked egg masses of either species. Wood frog egg masses were observed in 29 pools, and ten pools contained spotted salamander egg masses. Only a single pool contained just spotted salamander egg masses.  As Jim Curatolo told me in a conversation last week, in his experience, wood frogs colonize new pools more quickly than spotted salamanders. This may be due to one or a number of factors, such as their relatively greater vagility, or perhaps their social advantage of vocal communication. A single male wood frog that finds a new pool and commences calling to draw in females may also attract other males in the vicinity. Silent salamanders have no comparable ability to exhibit mob mentality. Also, it is possible that philopatry is more pronounced in spotted salamanders relative to wood frogs. Finally, population trend differences in the two species may see the wood frog population surging, while spotted salamander population is static or declining, or less spotteds are emerging to breed this year after their banner year in 2010.

This begs the question: from where did all these wood frogs come?! Is there indeed a population surge occurring? Or is there a carrying capacity for egg masses according to the size and number of available aquatic habitats? While bigger ponds do have a tendency to have more egg masses, it is unknown how this effect occurs: do density effects in the aquatic habitat actually dictate the number of females that return upon maturing, or do adults exercise choice in avoiding aquatic habitats with many masses when there are other options available that will be less crowded for their offspring? In cases where options do not exist, it is hard to imagine animals foregoing breeding if only crowded conditions are available, either waiting for better, less crowded conditions the next year, or even better, for USC to augment the amount of habitat available!

It will be very interesting to see what is the pattern in the pre-existing pools, which I hope I can survey on Monday....

Jim Arrigoni, SUNY-ESF

At long last...

Temperatures in the 80s on Monday finally vanquished this seemingly never-ending winter, liberating almost all of the pools of ice. And despite the failure of forecasted thunderstorms to materilize, the amphibians responded throughout Heiberg Forest. After visiting each of the pools on Tuesday 12 April, I'm very pleased to report that wood frogs were observed lurking in the majority of Hexagon pools, and they have deposited egg masses in seven of them. No spotted salamander egg masses have yet been observed, but I think they are forthcoming; nocturnal visits revealed their presence in two of the Hexagon pools, as well as a few pools with spermatophores.

In the Microarray, wood frogs and spermatophores were observed in a few pools in both the field and forest, and a single wood frog egg mass in Pool #17 in the field. But Pool #30 seems to be the place to be: five wood frog and four spotted salamnder egg masses. This pool also was popular with breeding toads shortly after it was constructed last spring. It is large (5 m diameter), shallow (25 cm deep), and did NOT receive an organic topsoil layer. I wonder whether these factors actually matter, or whether Pool #30 is simply the fashionable place to be? Given that calling is still ongoing amidst drenching rains last night and today, and oviposition in pre-existing pools as of yesterday was far less than observed last year, my hunch is that there are many more egg masses to be distributed. Stay tuned....

-Jim Arrigoni, SUNY-ESF

Microarray Pool 30 on 12 April 2011

I repeat, it's still winter at Heiberg

I visited all 71 pools on Saturday the 9th, and observed quite a bit of variation in terms of hospitability for amorous amphibians. Some pools were entirely encased in ice and snow:

Whereas others looked absolutely inviting:

The majority of pools were largely covered with ice, but with a small areas of open water. Aside from last year's green frog tadpoles observed in a handful of pools, there was no sign of breeding activity in any of the pools: no egg masses, no spermatophores. This was also the case in a few of the pre-existing pools in the hexagon landscape that have historically been popular oviposition sites, so apparently the breeding season has yet to get underway anywhere at Heiberg. In contrast, large numbers of spotted and Jefferson salamanders and wood frogs were observed on the night of 4 March at the amphibian hotspot Labrador Hollow, which is about 3 km to the northeast, but ~150 m lower in elevation. Stay tuned, spring has to be nearing....

Jim Arrigoni, SUNY-ESF

It's still winter at Heiberg

The last day of March marked the first anniversary of groundbreaking of the 71 pools constructed in 2010. This year, winter lingers.

-Jim Arrigoni, SUNY-ESF

Pitfall trapping underway

With the help of 16 SUNY-ESF undergraduate volunteers, 18 drift fence/pitfall trap arrays were installed at Heiberg over the Labor Day weekend. Each array consists of a 5-meter section of polyethylene tarp (the fence) and six 5-gallon buckets (the pitfalls) buried in the ground adjacent to the fence.

Half of the pitfall trap arrays are located in close proximity to the 39 pools that consititute the Hexagon Array, and half are distributed elsewhere throughout the forest, several hundred meters from recently constructed pools. The latter group will serve as controls with which to compare the amphibian population impacted by pool construction. Traps were opened on 9 September and undergraduate interns have been diligently checking them since, recording species ID and length of each animal. So far we have encountered robust numbers of seven species: American toads, green frogs, pickerel frogs, wood frogs, red-backed salamanders, red efts of eastern newts, and spotted salamanders.

We intend to repeat the effort next year and in 2012. Since the hexagon pools were constructed in early June, no wood frog or spotted salamander breeding occured in them. Green frogs have bred in approximately a quarter of these pools, but their tadpoles require a year to develop before metamorphosing, so we will not expect to see recruited froglets until next year. One single pool did have a late pair of American toads breed soon after it was created, and these have completed larval development. With the exception of this single clutch of toads, this year's trapping should represent Time Zero -- essentially a perspective of the landscape before being impacted by amphibian production associated with the pools. If the pools are functioning as breeding habitats for vernal pool-associated species, we expect to see a relative increase in metamorph wood frogs and spotted salamanders next autumn, and as we catch up with demographic lag times, increases in relative abundance of adults of these two species.

More images of the trap construction process can be viewed by clicking here.

-Jim Arrigoni, SUNY-ESF