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Early Species Recognition in the Golden-Crowned Sparrow ( Zonotrichia atricapilla)
Learned behavior has long fascinated biologists due to its ability to decouple traits and genes, potentially either inhibiting or promoting the evolution of reproductive isolation between populations. In order to predict which outcome is most likely, it is necessary to understand the mechanisms by which behaviors are learned, including the filtering of inappropriate signals. In white-crowned sparrows (Zonotrichia leucophrys), the timeline and innate constraints on learning are well understood thanks to decades of research in the lab, allowing researchers to manipulate and measure behavior at the correct time to study the variable of interest. The closely-related golden-crowned sparrow (Z. atricapilla) can discriminate between white-crowned and golden-crowned sparrow song in the field while still in the nest, prior to the presumed onset of song learning. In this thesis, I investigated what mechanisms underlie this early recognition ability, and how they could prevent mistaken learning where the two species breed sympatrically. Specifically, I asked 1) Can you predict what characteristics are used for recognition, based on universal and distinctive in the species’ song? 2) Are other song elements used in nestling recognition? 3) Is nestling recognition affected by early acoustic experience? To address these questions, I conducted playback experiments to nestling golden-crowned sparrows (prior to the putative onset of learning) to test their ability to discriminate between conspecific and heterospecific (white-crowned sparrow) introductory whistles, and between local and foreign dialects of conspecific song. I found that nestlings were able to discriminate the two species based on introductory whistles alone; surprisingly, however, they did not discriminate between foreign conspecific and heterospecific songs. Next, I recorded the acoustic environment at each nest and tested whether amount of exposure to white-crowned sparrow song explained some of the variation in response to this species’ song by golden-crowned sparrow chicks. I found that exposure to heterospecific songs had no effect on response those stimuli in this population. Future genetic work in this species pair should determine whether their phenotypic and behavioral differences arose since very recent speciation, or if the two species are long-separated but experienced limited hybridization, and perhaps reinforcement against hybridization, upon secondary contact.
Hudson, Emily J, "Early Species Recognition in the Golden-Crowned Sparrow ( Zonotrichia atricapilla)" (2018). ETD collection for University of Nebraska - Lincoln. AAI13418941.