That would fit with the concept of selection for “honest signals”-that is, signals that convey information about an individual's underlying genetic, developmental, or epigenetic condition that cannot be cheated. The research team hypothesized that stress to the birds’ immune system during this early stage could put those key nuclei at risk, causing the birds to develop less complex songs. Then approximately 30 to 90 days after hatching, each bird practices, refines, and crystallizes the song he will sing for life.īoth the volume and connectivity of the brain cells responsible for song learning and production increase around this time in the young bird’s life. From roughly 15 days to 60 days after the birds hatch, they learn songs from older “tutor” males. In zebra finches, song development occurs in two overlapping stages. “A lot of the ways in which birds learn and process songs are similar to how humans learn and process and produce language.” “Song is a cool system in zebra finches, because it’s been used as a model system for understanding human language learning,” Merrill said. Scientists believe that songs with more elements, especially unique elements, and song phrases are more challenging to learn and produce, and that females prefer those songs. Each element can be unique, or a male can recycle an element and use it multiple times they also can combine elements into phrases. Each male typically produces one song that is composed of different elements. “Beak coloration may be more important as a signal to other males, as a sign of dominance and competitive ability.” Rather than appealing directly to female zebra finches, beak color may influence the hierarchy among males, and that hierarchy in turn may affect which males the females choose as mates.įemale zebra finches also assess song quality when choosing mates. Both reflect an individual in good condition,” Merrill said. “Beak coloration has been linked to attractiveness, but it’s not clear whether females actually prefer males with brighter red bills, or whether that co-varies with other characteristics, like song complexity. There’s sort of a cap on how ‘sexy’ or red his beak can be,” Merrill said. While beak color can fluctuate throughout a bird’s life based on diet and health, for a KLH-treated bird “the upper limit of his coloration seems to be set in that early-life period. The males treated with KLH (keyhole limpet hemocyanin, a molecule that stimulates an immune response) “had duller, less colorful beaks, and that impact lasted throughout their lives.” “That’s what we saw with beak coloration,” Merrill said. Previous studies found that challenges like infection or lack of nutritious food early in life could lead to poorer outcomes for adult birds, so the team expected that when they activated the young males’ immune systems by treating them with an antigen, those birds would sing less complex songs later in life. “That caught us totally off guard,” said Loren Merrill, a postdoctoral researcher at the Illinois Natural History Survey who was lead author on the study conducted with principal investigator Jennifer Grindstaff, an associate professor at Oklahoma State University. Stressed males wind up with duller, less colorful beaks but sing more complex songs. But rather than being uniformly negative, a recent study published in Functional Ecology found that the consequences of stress are mixed. A bout of early-life stress can have lifelong impacts on two key signals that help male zebra finches attract mates: beak color and song complexity.
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