Participants:
Kathy Jouvenat, Christa Lundberg, Michael Novemsky, Mike McCay(resource), George Wang(resource)

Site:  La Selva
Keywords:  Agalychnis saltator, parachuting, horizontal displacement, mass, average velocity, displacement.
 

Summary:
To determine how mass affects velocity and how length affects horizontal displacement in flight for A. saltator frogs, we measured flight displacement, angle from horizontal, and time of flight for 18 frogs jumped from approx 5m high. We found that more massive frogs flew slightly faster and no relation between length and horizontal displacement.

Introduction:
Agalychnis saltator and Agalychnis callidryas are two species of frogs known for their parachuting abilities. A recent study (Roberts, 1994) showed that A. saltator participate in explosive breeding, and use their parachuting abilities to quickly get down to the swamp from the lianas above. The explosive breeding occurs only after a period of heavy rain. Amplexing pairs then use lemuriform (hand-over-hand) locomotion to crawl up the liana, where they lay their eggs in moss over the water.

The ability of A. saltator to parachute down to the swamp allows them to gather very quickly for breeding. As they parachute, they perform a controlled leap, with legs spread wide from the body, toe pads and webbing wide apart. The landing pad is a broad-leafed plant. The parachuting behavior is seen only in mating, not in predator avoidance.

We investigated two things: frog mass vs. speed , and frog length vs. horizontal distance of jump. We would presume that bigger frogs would travel further at a higher average velocity, which might give the bigger frogs the advantage in the mating world of frogs.

Methods:
Seven A. callidryus, and eleven A. saltator had previously been collected in the Research Swamp by Mike McCay and George Wang, both from the University of California, Berkeley. Mike and George had also devised the method by which we would test each frog for 5 jumps. We used the second floor balcony of the Old Classroom to achieve a vertical height of 5m for the frogs to jump. The railing served as the launching pad. George duct-taped a tarp to the building and extended it over a concrete ditch to the grass in order to cushion the landing surface for the frogs. Mike taped the end of a measuring tape to the launching pad so that we could measure the distance and angle of the jump. George had rigged up an old fishing reel and zip-loc bag to be the frog elevator, returning the same frog to the launch pad for 4 more jumps. Mike and Michael both timed each jump with digital watches. Mike also set up 2 camcorders to record the jumps for when he analyzes jumps later in his research.

George and Christa removed a frog from the container, measured it from snout to vent in mm, and massed it in g. They also determined species and sex, which were recorded. The insecticide DEET was not allowed on anyone touching the frogs, due to the porous nature of their skin. Christa or George set the frog on the launching pad. Christa yelled "Frog on the pad!" to alert those of us below that a jump was imminent.

Mike and Michael observed by sight for the beginning of the jump to start their timer. Christa used her finger to tap the frog on the posterior end in order to encourage jumping. Often, the frog jumped. Just as often, the frog crawled around the rail, and Christa had to wrestle it back into launch position. If a frog refused to jump it was returned to the container, and Christa or George selected another frog. Mike and Michael visually spotted where the frog landed and the time of the jump. Mike captured the frog and placed it in the frog elevator to return to the launching pad. Michael determined the distance and angle of the jump using the tape measure and compass declinometer. Kathy recorded the time, distance, angle, and other observations, such as direction of jump from center.

Results:
We found a slight correlation between frog mass and velocity as shown in Fig. 2.
We found no significant correlation between frog length and horizontal distance traveled as shown in Fig. 3.

Discussion:
As expected, more massive frogs fly slightly faster, probably due to lower cross sectional area/weight ratio. This is less obvious. Times, and therefore speeds, were not precisely measured for this study. This relation can be more accurately determined using video of the trials.
Length of frog had no significant effect on horizontal distance traveled. A. callidryas frogs would not jump during our experiment, so we did not use them.

Acknowledgements:
A huge thanks go to Mike McCay and George Wang for allowing us to join right in on their ongoing research.

Literature Cited:
Roberts, W.E. 1994. Explosive Breeding Aggregations and Parachuting in a Neotropical Frog, Agalychnis saltator (Hylidae). Journal of Herpetology Vol.28 No.2 pp.193-199.
 
 

Appendix 1: The Essential Question -- Classroom Extensions:
        A. Inquiry: Simulation Suggestions
            1.  Students construct paper "frogcopters" to test variables and how they affect hang time
                a. variable suggestions - length, width, mass
                b. constants - height
            2.  Students construct model frogs
                a. use saran wrap between frog toes to simulate webbing
                b. use heavier paper or poster board to simulate frog body
                c. catapult frog models off launching pad with finger flick or slide frog models off 45 degree slope
                d. vary amount of webbing and frog body size to see how glide is affected
        3.  Students learn about Bernoulli's Principle with parachuting frogs as one example
        B.  Inquiry simulation generates questions for research projects on environmental science
             1.Examples of questions on frogs and their habitat
                a. what type of habitat do A. saltator and A. callidryus require? (similarities, differences)
                b. what environments do the frogs require in order to reproduce?
             2. Examples of questions on frogs and the tropical rain forest biome
                a. why is primary growth forest essential to the frogs' survival?
                b. how does the behavior of the frogs change from the dry season to the rainy season?