In this paper, the authors investigated various properties of the adhesive characteristics of the tongues of horned frogs when they strike prey. The authors had a striking pad connected to a cantilever to measure forces. They also used high speed cameras to capture the strike and record relevant data.
To get an idea of the experimental set up, you can check out this movie, kindly sent to me by Thomas Kleinteich. If video does not play in your browser, you may download it here.
The data files
I pulled data files from the Kleinteich and Gorb paper. You can download the data files here: https://s3.amazonaws.com/bebi103.caltech.edu/data/frog_strikes.zip.
There are four files, one for each of the four frogs, labeled with IDs I, II, III, and IV, that were studied. To see the format of the files, we can look at the content of the file for frog I. You can use
head -n 20 ../data/frog_strikes_I.csv
from the command line. Here is the content of the first data file.
# These data are from Kleinteich and Gorb, Sci. Rep., 4, 5225, 2014.
# Frog ID: I
# Age: adult
# Snout-vent-length (SVL): 63 mm
# Body weight: 63.1 g
# Species: Ceratophrys cranwelli crossed with Ceratophrys cornuta
date,trial number,impact force (mN),impact time (ms),impact force / body weight,adhesive force (mN),time frog pulls on target (ms),adhesive force / body weight,adhesive impulse (N-s),total contact area (mm2),contact area without mucus (mm2),contact area with mucus / contact area without mucus,contact pressure (Pa),adhesive strength (Pa)
2013_02_26,3,1205,46,1.95,-785,884,1.27,-0.290,387,70,0.82,3117,-2030
2013_02_26,4,2527,44,4.08,-983,248,1.59,-0.181,101,94,0.07,24923,-9695
2013_03_01,1,1745,34,2.82,-850,211,1.37,-0.157,83,79,0.05,21020,-10239
2013_03_01,2,1556,41,2.51,-455,1025,0.74,-0.170,330,158,0.52,4718,-1381
2013_03_01,3,493,36,0.80,-974,499,1.57,-0.423,245,216,0.12,2012,-3975
2013_03_01,4,2276,31,3.68,-592,969,0.96,-0.176,341,106,0.69,6676,-1737
2013_03_05,1,556,43,0.90,-512,835,0.83,-0.285,359,110,0.69,1550,-1427
2013_03_05,2,1928,46,3.11,-804,508,1.30,-0.285,246,178,0.28,7832,-3266
2013_03_05,3,2641,50,4.27,-690,491,1.12,-0.239,269,224,0.17,9824,-2568
2013_03_05,4,1897,41,3.06,-462,839,0.75,-0.328,266,176,0.34,7122,-1733
2013_03_12,1,1891,40,3.06,-766,1069,1.24,-0.380,408,33,0.92,4638,-1879
2013_03_12,2,1545,48,2.50,-715,649,1.15,-0.298,141,112,0.21,10947,-5064
2013_03_12,3,1307,29,2.11,-613,1845,0.99,-0.768,455,92,0.80,2874,-1348
2013_03_12,4,1692,31,2.73,-677,917,1.09,-0.457,186,129,0.31,9089,-3636
2013_03_12,5,1543,38,2.49,-528,750,0.85,-0.353,153,148,0.03,10095,-3453
2013_03_15,1,1282,31,2.07,-452,785,0.73,-0.253,290,105,0.64,4419,-1557
2013_03_15,2,775,34,1.25,-430,837,0.70,-0.276,257,124,0.52,3019,-1677
2013_03_15,3,2032,60,3.28,-652,486,1.05,-0.257,147,134,0.09,13784,-4425
2013_03_15,4,1240,34,2.00,-692,906,1.12,-0.317,364,260,0.28,3406,-1901
2013_03_15,5,473,40,0.76,-536,1218,0.87,-0.382,259,168,0.35,1830,-2073
The first lines all begin with #
signs, signifying that they are comments. They do give important information about the frog, though.
The first line after the comments are the headers, giving the column names for the data frame we will load.