Doctor of Philosophy
Scott A MacDougall-Shackleton
David F Sherry
Effective navigation and orientation is essential for animals to survive. The study of migratory birds provides insights into these processes, particularly through mechanisms like the geomagnetic compass, which uses Earth's magnetic field for directional information. A brain region in songbirds relevant to this is cluster N, known for its potential role in processing geomagnetic information. Notably, cluster N appears exclusive to nocturnally migratory birds, being active solely at night, and lesion studies reveal that an intact cluster N is necessary for geomagnetic compass orientation. However, given the scarcity of empirical data concerning cluster N, substantial questions persist regarding its function. This thesis aimed to expand our understanding of cluster N. I addressed three key research questions in three experiments: 1. Is cluster N's activation flexible or circadian-controlled? (Chapter 2), 2. Is cluster N's activity linked to migratory flight? (Chapter 3), and 3. Do non-migratory birds possess cluster N, despite prior assumptions? (Chapter 4). Results in Chapter 2 demonstrated that cluster N is flexibly activated, with cluster N activity correlating with nocturnal migratory restlessness rather than circadian control. In Chapter 3, investigations on yellow-rumped warblers did not reveal associations between migratory flight in a wind tunnel and cluster N activity, nor associations between flight and activity in the hippocampus—a region crucial for spatial memory. In chapter 4, I found no differences in cluster N or hippocampus activity between zebra finches that were either trained to use magnetic cues to find food or those assigned to a control condition (i.e., no training). However, patterns of neural activation hinted at potential cluster N activity in these non-migratory birds. Collectively, this research enriches our grasp of cluster N's role in orientation behaviour and migration in birds, and expands the study of cluster N to a wider range of bird species than previously studied.
Summary for Lay Audience
How do birds know where to go? Every year, millions of birds prepare to embark on a great journey–migration. While some songbirds do not migrate, they still need to know how to get around to find food, mates, and shelter. One of the many ways that birds navigate is through their perception of Earth’s magnetic field. Invisible to human beings, birds sense this force, and can use it, almost like a compass. I study songbirds’ brains to understand how songbirds perceive magnetic fields. One brain region, called cluster N, is deemed important for some migratory songbirds to “see” the magnetic field at night. In my PhD work, I wanted to answer new questions about cluster N: When birds “want” to migrate, does cluster N “turn on”? Does cluster N “turn on” when birds fly? Can cluster N be found in non-migratory birds that also perceive electromagnetic fields? By attempting to answer these questions, we will further understand how songbirds navigate with their eyes for the invisible. In my studies of cluster N, I found that when birds are restless (or demonstrate motivation to migrate), we see a greater activity in cluster N compared to birds which are not restless. Concerning the activation of cluster N during flight in birds, I did not find that cluster N turns on only when birds are flying. In addition, based on preliminary evidence, I learned that cluster N is likely present in at least one non-migratory species (i.e., zebra finch) that may use magnetic information to orient outside of migration flights. These findings provide a deeper insight into the role of cluster N, an understudied brain area in birds, during migration.
Brodbeck, Madeleine IR, "Neural responses to magnetic orientation information in songbirds" (2023). Electronic Thesis and Dissertation Repository. 9773.
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