Page 11 - Black Range Naturalist, April 2020
P. 11

 heteromyid rodents forage, they use the forelimbs to push seeds into the external cheek pouches. When seeds are abundant, the heteromyid rodents look like they have mumps, with the cheek pouches stuffed full of
and Ord’s Kangaroo Rat (approximately 30 grams each or eleven or twelve ounces). Before the cattle industry reduced the perennial grasslands to patches, there was little overlap between Merriam’s Kangaroo Rats and Ord’s Kangaroo Rats. Merriam’s seemed to prefer the open shrub- dominated areas while Ord’s preferred grassy habitats. In an experiment where we killed shrubs with a herbicide, there was a rapid expansion of grasses, especially the grama grasses, bush muhly, and tobosa grass. Initially the Ord’s Kangaroo Rats were most abundant, but during a series of drought years, Merriam’s Kangaroo Rats became dominant. Our initial assessment that the Ord’s Kangaroo Rats benefitted from the increase in grass cover was not substantiated by the results of the more than 10-year study of the treated area in comparison to untreated shrubland.
seeds. Cheek pouches allow the rodents to take advantage of large seed rains plus minimize the time spent out of the burrow where they are subject to a whole list of predators including owls, snakes, coyotes, and badgers. Heteromyids store some seeds in their burrow system but also “scatter hoard” - that is, they bury the contents of the cheek pouches in excavated caches near the main burrow system. Since the rodents do not always remember where caches are located, they serve to generate species of plants that are preferred seeds. The most desirable seeds are of the annual grama grasses that complete their life cycle in six weeks and therefore are
called six-week gramas. When the annual gramas are in fruit and seeds are falling from the plants, heteromyids forage almost exclusively on the six-week grama seeds.
When we were
funded by the
International
Biological
Programme, I
had two graduate
students who were
deep into their
research. As a consequence, I hired an undergraduate student to assist with trapping, and one who was a good entomologist. Since we were working on a watershed dominated by creosotebush, I gave the students a choice of the sloping bajada (piedmont) or the trap grids at the base of the watershed: a dry lake. Needless to say, I opted for the bajada while most students chose the dry lake. The students quickly learned about cold air drainage. Cold air is denser than warm and quickly settles on the dry lake. After conferring with the other students, we settled on a compromise: dry lake one night and bajada the next night.



One of the undergrads, who later worked for the Texas game department, had lost his leg in a motorcycle
accident. Once when setting traps on the dry lake, he stepped into a crack in the clay and twisted his foot pointing to the rear. He continued to set traps with one foot forward and the other to the back. The other students thought this was great because it offered a bit of humor for them.
Kangaroo rats vary greatly in size and type of burrow system that they utilize. There are two species of kangaroo rats that are nearly the same size: Merriam’s Kangaroo Rat 1
When cleaning and baiting traps, we occasionally noted locations of pack-rat middens and made certain that we would capture the resident. As I tried to extricate a rat from the trap, it bit my index finger to the fascia and tendons. That caused me to
dance around
trying to staunch the blood, and I
am confident that the students working the dry lake heard me and I heard lots of laughter. The next night the students insured that I would cover the bajada. When they baited the traps, they placed a rock weighing approximately 200 grams in the trap near the midden. When I picked up the trap and felt the weight, I was convinced that the resident was a very large pack rat. I started yelling (XX##%%&&@) I heard gales of laughter from the students, who had really convinced the professor that there was a large vicious rat in the trap.
One visual that I will never forget was a Merriam’s kangaroo rat that I released from the trap. The kangaroo rat took three hops to get under a creosotebush and into the jaws of a Western Diamondback Rattlesnake. The snake struck the rodent, who took 3-4 hops before dropping and
quivering. The rattlesnake used it’s Jacobson’s organ in its mouth to locate the prey. The snake slowly made its way to the carcass, and swallowed the rat head first.
Merriam’s and Ord’s Kangaroo Rats maintain fairly stable populations, with recruitment dependent upon the production of annual grasses. The two species were
 A banner-tail kangaroo rat – body mass 48 ounces. Note the white terminus of the tail which gives the rodent the common name of banner-tail (photo by Dr. David Lightfoot).
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