To cite the 'circular' package in publications use:

C. Agostinelli and U. Lund (2017). R package 'circular': Circular Statistics (version 0.4-93). URL https://r-forge.r-project.org/projects/circular/

Corresponding BibTeX entry:

  @Manual{,
    title = {{R} package \texttt{circular}: Circular Statistics
      (version 0.4-93)},
    author = {C. Agostinelli and U. Lund},
    address = {CA: Department of Environmental Sciences, Informatics
      and Statistics, Ca' Foscari University, Venice, Italy. UL:
      Department of Statistics, California Polytechnic State
      University, San Luis Obispo, California, USA},
    year = {2017},
    url = {https://r-forge.r-project.org/projects/circular/},
  }