Madden, J. R., Kunc, H. P., English, S., Manser, M. B., & Clutton-Brock, T. H. (2009). Calling in the gap: Competition or cooperation in littermates' begging behaviour? The Royal Society.

Madden, Joah R., Hansjoerg P. Kunc, Sinead English, Marta B. Manser, و Tim H. Clutton-Brock. Calling in the Gap: Competition or Cooperation in Littermates' Begging Behaviour? The Royal Society, 2009.

Madden, Joah R., et al. Calling in the Gap: Competition or Cooperation in Littermates' Begging Behaviour? The Royal Society, 2009.