A study on sleeping finches found that their sleep is quite complex. The slumbering finches experienced slow wave sleep (SWS), rapid eye movement sleep (REM), intermediate sleep (IS), and K-complex sleep, which aids memory consolidation in human beings. REM episodes were brief early in the night but became longer as REM density increased and intervals between REM sleep decreased. Unihemispheric sleep (sleep with one eye open) was less common, of a shorter duration, and almost exclusively restricted to the light phase of sleep: think napping over deep sleep (“I’m not sleeping, I’m just resting my eyes!”).
Why is complex sleep important? Bird brains don’t look a whole lot like our brains. Given the lack of structures like a neocortex, human researchers have tended to assume that birds aren’t capable of complex neurological activity, including dreaming. But studies like this show that birds are much more complicated and intelligent than we think. The ethology of crows (and some other birds) has proven that birds have a sense of past and future, which allows them to plan, change and weigh consequences, and refrain from unproductive actions. Some of this stored information is replayed while sleeping, which may help birds develop memories, practice daily activities, or process events. So what were the zebra finches dreaming about? The same study found that the sleeping finches replayed, rehearsed, and perhaps improvised songs in their sleep. In short, songbirds – at least these songbirds – dreamed of singing.
Do eagles experience complex sleep? We don't know, although the authors of the zebra finch study state that there could exist a greater complexity to sleep structure across bird species than has commonly been recognized. Eagles experience many of the behaviors we see in birds like crows, which are renowned for their intelligence: language, delinquency, insight, emotion, frolic, passion, wrath, risk taking and awareness. Eagles organize in social multi-age groups away from their territories, follow consistent migration paths between winter and summer grounds, select and retain mates, build large, complex nests, incubate and brood young in challenging conditions, teach their young, learn from life events, and recognize and remember things on their territories. They clearly have intellect, even if it isn’t organized much like our intellect, and they most likely experience complex sleep. Perhaps our question should be not "Do eagles dream?" but rather, "What do eagles dream about?".
We reached out to Marge Gibson from the Raptor Education Group, who responded that her birds (a macaw, doves, and a turkey) dream and vocalize while dreaming. Several forums on pet birds, especially Psittaciformes, discuss dreaming in birds, although I wasn't able to find many videos of the behavior.
Things that helped me learn about sleep in birds:
- Mammalian-like features of sleep in zebra finches: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440357/
- Plumes in the sleeping avian brain: https://www.mpg.de/7984169/avian-sleep-brain-activity
- A phylogenetic analysis of the correlates of sleep in birds (regrettably, no Accipitridae were included): http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2869.2006.00559.x/full
- Brain basis of self: self-organization and lessons from dreaming (a tough but interesting read): http://journal.frontiersin.org/article/10.3389/fpsyg.2013.00408/full
- Zebra finches learn songs from their fathers: http://www.upi.com/Science_News/2015/11/30/Study-Zebra-finches-learn-songs-from-their-fathers/4211448915702/
- Animals have complex dreams, MIT researcher proves: http://news.mit.edu/2001/dreaming
- The role of slow wave sleep in memory processing (I need to go back and read this again): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2824214/
- What do animals dream about? http://www.bbc.com/future/story/20140425-what-do-animals-dream-about
- What do birds dream about? http://articles.chicagotribune.com/1998-12-17/news/9812180355_1_birds-dreaming-ra
- Thanks to John Howe, Sherri Elliott, and Robin Brumm for noting the behavior, finding the video, and contributing to the blog, and to Sherri for reaching out to Marge Gibson.
- Lucid Dreaming Sleep Track (8 Hour Sleep Cycle Track) with Binaural beats and Isochronic Tones: https://youtu.be/mDX8QrcDI_o
This blog addressed primarily avian dreaming, but avian sleep is an interesting topic and we'll return to it in another blog!