Effects of light attraction and flight-calling on mortality of nocturnally migrating songbirds
LE3 .A278 2021
Bachelor of Science
Migration is observed in many species of the animal kingdom, including birds. Of increasing risk to nocturnally migrating birds is mortality associated with attraction to artificial light. During migratory flights, some birds produce species-specific vocalisations known as flight calls, which are believed to facilitate group cohesion and collective decision-making. Artificial light has the ability to disrupt compass systems used by migrants, disorienting them. Studies have suggested that flight-calling may contribute to mass collision events by amplifying disorienting effects of light at night. Migrants increase flight-calling in response to light, possibly attracting more conspecifics that are then at greater risk of light-related mortality. Light may also negatively affect decision-making capacity, leading to poorer decisions during migration. To examine this, I used data from the Breeding Bird Survey (BBS) to determine if flight-calling species have experienced greater population declines between 1966 and 2017 than non-flight-calling species. Analysis supported this hypothesis with 74% of flight-calling species continent-wide showing declines. There was a greater proportion of negative trends in the western BBS region (71%) versus the two other regions. However, further research is required to determine if these effects are attributable to increased anthropogenic light, or other mortality sources which have increased in tandem, such as habitat loss and habitat degradation.
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