Effects of Anthropogenic Noise on Songbird Social Networks

Anthropogenic noise, which is increasing globally, affects birds from gene expression up through alteration of community composition. as urbanization pushes further into undisturbed habitat, noise often disperses birds away from the point source. The impacts of this dispersal on surrounding quieter areas is not well understood. Therefore, in the first chapter, we sought to understand how noise-related dispersal affected the sociality of groups of songbirds as they moved away from the source of noise. as the displaced birds would likely be forced to occupy a smaller area that may already have resident individuals, we predicted that displaced birds would show a tighter clustered social network that may include new individuals, and that individuals within the flock would have more social connections overall. in the second chapter, we were interested in chronic, inescapable noise, the kind that birds living in urbanized areas might experience, and how that affects sociality. We predicted that birds would distribute themselves along a noise gradient and prefer the quieter areas and that the resulting density of birds would increase both flock clustering and individual sociality. We tested these ideas in two songbird systems, free-living red-backed fairy wrens (Malurus melanocephalus) to study dispersal and captive domesticated zebra finches (Taeniopygia guttata) to study chronic noise exposure. Contrary to our prediction, the free-living red-backed fairywrens became less social when dispersing from noise, as measured by node strength, during experimental noise treatments. Additionally, these birds tended to shift their space use away from the sound source. in our captive system, our hypothesis was supported that both flock cluster and individual sociality increased with noise treatments. However, the birds did not alter their distribution in accordance to the noise gradient, thus we propose support for the Increased Threat Hypothesis and suggest that increased vigilance was responsible for flock clustering and sociality. If social networks are altered consistently, there may be implications for future breeding success, detection of communication signals, and even for pathways of disease transmission among individuals