Glossary of "Life (9th ed.)" by Sadava et al. (2011)
- The life stage during which some particular type of learning must take place, or during which it occurs much more easily than at other times. Typical of song learning among birds.
- Sadava, D., Hillis, D. M., Heller, H. C. & Berenbaum, M. R. 2011. Life: The Science of Biology, 9th ed. -xliv + 1266 pp. Sinauer Associates, Inc., Sunderland.