Viruses infect organisms in all domains of life and are abundant entities in ecosystems. In particular, single-stranded DNA viruses have been found in a wide variety of hosts and ecosystems. Using a metagenomic approach, novel circular viruses have been identified in multiple environmental samples. This thesis focuses on viruses and virus dynamics from avian sources. As part of this thesis, a novel phapecoctavirus was identified in a pigeon cloacal swab. The phapecoctavirus is most closely related to Klebsiella phage ZCKP1, identified from a freshwater sample. Beyond this, this thesis addresses circoviruses, which are of interest due to disease they cause to avian species. Evolution of circovirus recombination was studied in a closed system of uninfected and infected pigeons. 178 genomes of pigeon circovirus were sequenced, and patterns of recombination determined. Seven genotypes were present in the population and genotype 4 was shown to be present in a majority of samples after the experiment was finished. Circoviruses were also identified in waterfowl feces and the ten genomes recovered represent two new circovirus species. Overall, the research described in this thesis helped to gain a deeper understanding of the diversity and evolution of circular DNA viruses associated with avian species.