A flash of fur. A hint of whisker. That is usually what I see of the two desert shrews (Notiosorex crawfordi) that are participating in a prey capture and handling study that I am conducting with my faculty sponsor, Dr. Cecil Schwalbe. At about 4.5 grams, these shrews are small and fast. And, unfortunately, they are also quite shy. This makes videotaping them quite a challenge!
What is a shrew anyhow? Shrews belong to the order Insectivora and as such, their diet is composed almost entirely of invertebrates (although they eat rodents, amphibians and reptiles as well). They are known for being fierce predators, with some species needing to consume more than their own body weight in food every day. Some shrews have even been observed attacking prey larger than themselves.
The desert shrew seems to need about 70% of its body weight in food daily to maintain its weight. Adapted to arid environments, the desert shrew obtains all of its water from the food that it eats. It can also enter torpor, a state of lowered metabolism, in order to conserve resources and to deal with high desert temperatures.
But why study desert shrews? Very little is known about the behavior of this species. Dr. Schwalbe had the opportunity to observe them while he was a graduate student. His officemate at that time, Stan Lindstedt, did his doctoral research on the physiology of N. crawfordi in Dr. William Calder's lab here at the UA. Based on some of those early observations, this study is designed as a preliminary attempt to assess prey preference and prey capture techniques; i.e., do shrews employ different methods to kill potentially dangerous food items than those used on harmless prey?
Some of our preliminary data show that they do. N. crawfordi will dispatch harmless prey such as crickets with a bite to the head or neck. Often the shrew will simply immobilize the insect and then cache it in a corner of its terrarium to be eaten later. However, when presented with a more formidable insect, such as a field grasshopper, the shrew attacks in order to disable the dangerous parts before killing it with a bite to the head. Grass-hopper jumping legs are bitten at the joint next to the body which often severs the leg completely. Scorpions are attacked from the rear, where the shrew bites the telson before going for the head.
Much to my surprise, one shrew attacked a bark scorpion, biting the tail but then attacking the head before disabling the stinger. On video, it appears that the shrew was stung several times, yet it shows no adverse reaction to the poison. Perhaps shrews possess a natural defense against such venom? Or perhaps their fur provides enough protection that the stinger cannot penetrate the skin? I don't know which it is yet, but it is fun to ponder the possibilities.
The larger goal of this study was to try to assess whether some of these behaviors are instinctual or if they are learned. However, with only two shrews (neither of which are naive), this goal is not yet feasible. But, the study has introduced me to the field of animal behavior and has shown me how enjoyable it can be to sit back and watch life around you.
Bridget Watts, UBRPer in Dr. Schwalbe's lab, Wildlife and Fisheries Science