“All right, ladies, what do you know about animals active in the night?” I ask this question to begin a class taught after sunset. The class, Nocturnal Nations, is designed to empower students to begin overcoming fears of the night. Generally one to three students know the terms nocturnal and diurnal. When I ask leading questions toward crepuscular, however, I inevitably receive confused stares from everyone. By the end of class, my students are able to review adaptations in nocturnal animals and how these differ for diurnal animals, but the concept of crepuscular animals remains elusive for the students. (Although all there are non-mammal crepuscular animals, I will focus on mammals in this post.) By contrasting urban crepuscular mammals against mountain crepuscular mammals, students will better understand crepuscular animals.
Animals are active at particular times during the day; each species has a daily pattern of periods of activity, or circadian rhythm. For instance, humans find pleasure in being active during the day – ask students to wake up before dawn and they’ll complain! Crepuscular describes generally nocturnal animals with peak activity around dusk and dawn (Rich & Longcore, 2013, p. 20). One reason this category is harder to understand is that nocturnal and diurnal are often simplistically presented as binary opposites rather than ends of a spectrum of possible activity cycles. Crepuscular animals open to students the possibility that animals can be active at other times of the day, such as common muskrats, nocturnal though active on overcast days (“List of Mammals in California,” 2012). Because the three categories are different activity patterns over the course of a day, we teach all three as vocabulary.
Another reason the concept of crepuscular animals eludes students is simply that their experience with such animals is limited. There are crepuscular mammals in southern California, but the majority of crepuscular mammals live either in the Arctic or southern India and China (Bennie et al., 2014, p. 13728). With notable exceptions, crepuscular animals do not frequent urban areas – while undeveloped areas of southern California host about 33 species, fewer than ten species of crepuscular mammals are relatively common in the region’s urban areas (Albano et al., 2012). For example, grey foxes, coyotes, and raccoons’ wide diet as opportunistic feeders (California Wildlife Center, 2011) allow these three species to adapt to urban areas. In contrast, High Trails’ mountains support mule deer, coyotes, grey foxes, two species of vole, 5 species of rabbit, mountain lion, bobcat, lynx, and 19 species of bat (“List of Mammals in California,” 2012). Most of these species use their circadian rhythm to survive the daily temperature swings and to access food populations.
In class, I describe crepuscular in terms of the coyotes we inevitably hear during class. Many students arrive with first-hand experience with coyotes’ feeding habits; now they hear vocalizations of a coyote pack reverberate around our mountains. The example of coyotes gives students knowledge against their fears of the unknown night and creates a bridge into other crepuscular animals. Nocturnal Nations’ class time ends with each student challenging herself to walk a short distance alone without a flashlight in the national forest; afterwards, the students excitedly tell me of their new awareness of the nocturnal world around them.
Albano, G., Bitcon, T., Condamoor, M., Lao, S., Lopez, G., Sokolovsky, R., & Vicencio, A. (2012, June). Large Mammal Movement in the Eastern Santa Monica Mountains. UCLA Institute of the Environment and Sustainability, Los Angeles, CA. Retrieved from http://www.environment.ucla.edu/perch/resources/files/urbanwildlifemovement2012.pdf
Bennie, J. J., Duffy, J. P., Inger, R., & Gaston, K. J. (2014). Biogeography of time partitioning in mammals. Proceedings of the National Academy of the Sciences of the United States of America, 111(38), 13727–13732.
California Wildlife Center. (2011). Large Predator Facts. Retrieved October 31, 2014, from http://cawildlife.org/index.php/faqs/animal-profiles/96-animal-info/animal-wiki/198-large-predator-facts
List of Mammals in California. (2012, October 9). [Table]. Retrieved October 31, 2014, from http://www.mammalsociety.org/mammals-california
Rich, C., & Longcore, T. (2013). Ecological Consequences of Artificial Night Lighting. Island Press.
The coyote picture is courtesy of Eva, a coworker of mine. All the other pictures are mine.