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Giovanni Casotti
Professor
gcasotti@wcupa.edu
Department of Biology
West Chester University
Living on the Edge: A Day in the Life of a Hummingbird

This case study describes the daily osmotic struggle for survival faced by hummingbirds. The narrative is written from the viewpoint of a human observer who sees an Anna's hummingbird feeding on flowers outside of her window.  She notices that the birds mostly feed early in the morning and again in the evening at dusk; midday encounters are rare.  The case raises questions about floral nectar production, how this correlates to feeding bouts, and how this in turn correlates to the daily osmotic challenges faced by these nectarivorous birds and their allies (sunbirds). Students will learn about renal adaptations for survival and how they operate. Finally, since hummingbirds have a high metabolic rate and cannot feed overnight they undergo torpor during this time, an energy saving physiologic state.  Students read journal articles to answer case questions, which should lead them to a better understanding of the related physiological processes of osmoregulation, metabolic rate and torpor.


Lost? Ask a Turtle: Navigation and Migration in Loggerheads

This case study examines the events surrounding the hatching and migration of loggerhead sea turtles, specifically what mechanisms they use to head towards the ocean (once hatched) and where and how they migrate once in the ocean.  The story is written from the point of view of two hatchlings as they crack through their shells, dig out of the sand, and travel at night along the beach into the ocean.  Once they survive this peril, they make their way to the deep ocean and the North Atlantic current, migrating along it, until decades later the female makes her way back to the same beach to lay her eggs and begin the cycle anew.  The case details how loggerheads navigate these vast distances with seemingly no navigational cues.  The case also explores how other long-distance migratory species such as birds and seals migrate along similar vast distances. Originally written for a Masters-level class in biology called "Case Studies in Physiology," the case could easily be used or modified for senior or even undergraduate level biology-majors course.


The Deep: The Physiology of Decompression Sickness

This case study presents a fictional story in a realistic setting to teach aspects of human cardiovascular and respiratory physiology as they pertain to decompression sickness and its treatment options. Specifically, students learn about the partial pressures of gases in the circulatory system and how they change with depth and altitude. The case relates how Dan and Beth, a couple who operate a charter business for diving expeditions, take six tourists out to dive a shipwreck. When it comes time to ascend, one of the divers cannot be found and Dan must stay behind for the rescue. When he finds the missing diver, there is not enough air left in their tanks to rise slowly and safely decompress. They make it to the surface, but must be airlifted to the nearest decompression chamber for treatment. This case was developed for Masters-level students in biology, but could easily be adapted for an upper-level undergraduate physiology course.