To cite crawl in publications include both references:

Johnson, D. S., London, J. M., Lea, M.-A. and Durban, J. W. (2008) CONTINUOUS-TIME CORRELATED RANDOM WALK MODEL FOR ANIMAL TELEMETRY DATA. Ecology, 89: 1208-1215.<doi:10.1890/07-1032.1>

Devin S. Johnson and Josh M. London (2018). crawl: an R package for fitting continuous-cime correlated random walk models to animal movement data. Zenodo. https://doi.org/10.5281/zenodo.596464

Corresponding BibTeX entries:

  @Article{,
    title = {Continuous-time correlated random walk model for animal
      telemetry data},
    author = {Devin S. Johnson and Josh M. London and Mary-Anne Lea and
      John W. Durban},
    journal = {Ecology},
    year = {2008},
    volume = {89},
    number = {5},
    pages = {1208-1215},
    doi = {10.1890/07-1032.1},
    url = {https://doi.org/10.1890/07-1032.1},
  }

  @Misc{,
    title = {crawl: an R package for fitting continuous-cime correlated
      random walk models to animal movement data},
    author = {Devin S. Johnson and Josh M. London},
    year = {2018},
    doi = {10.5281/zenodo.596464},
    url = {https://doi.org/10.5281/zenodo.596464},
  }