To cite popbayes in publications use:

  Casajus Nicolas, Pradel Roger (2023). _popbayes: Bayesian model to
  estimate population trends from counts series_. R package version
  1.2.0, <https://frbcesab.github.io/popbayes/>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {popbayes: Bayesian model to estimate population trends from counts series},
    author = {{Casajus Nicolas} and {Pradel Roger}},
    year = {2023},
    note = {R package version 1.2.0},
    url = {https://frbcesab.github.io/popbayes/},
  }