Migratory Sleeplessness in the White-Crowned Sparrow (Zonotrichia leucophrys gambelii)

Abstract

Twice a year, normally diurnal songbirds engage in long-distance nocturnal migrations between their wintering and breeding grounds. If and how songbirds sleep during these periods of increased activity has remained a mystery. We used a combination of electrophysiological recording and neurobehavioral testing to characterize seasonal changes in sleep and cognition in captive white-crowned sparrows (Zonotrichia leucophrys gambelii) across nonmigratory and migratory seasons. Compared to sparrows in a nonmigratory state, migratory sparrows spent approximately two-thirds less time sleeping. Despite reducing sleep during migration, accuracy and responding on a repeated-acquisition task remained at a high level in sparrows in a migratory state. This resistance to sleep loss during the prolonged migratory season is in direct contrast to the decline in accuracy and responding observed following as little as one night of experimenter-induced sleep restriction in the same birds during the nonmigratory season. Our results suggest that despite being adversely affected by sleep loss during the nonmigratory season, songbirds exhibit an unprecedented capacity to reduce sleep during migration for long periods of time without associated deficits in cognitive function. Understanding the mechanisms that mediate migratory sleeplessness may provide insights into the etiology of changes in sleep and behavior in seasonal mood disorders, as well as into the functions of sleep itself.

Mammalian-like features of sleep structure in zebra finches

“…These features are similar to patterns of sleep staging in mammals (25,26). The total amount of REM sleep averaged 22.99 Ϯ 3.83% (mean Ϯ SEM) (Table S1) of the dark period, greater than reported in most avian sleep studies, including the few studies of oscines (13,14). The intermediate epochs were brief and numerous (Fig.…”

“…The observation of REM sleep is by itself an insufficient basis to equate avian and mammalian sleep patterns, except to distinguish them from reptilian sleep (27), where REM is poorly established (28), but other similarities of sleep architecture in birds and mammals have not been well established. Avian REM periods are reported to be extremely brief and infrequent in most species hence ''rudimentary'' (12) with the exception that oscine passerines have more REM (13,14,23,29). Mammalian sleep has a circadian distribution, is triphasic and is associated with precise electroencephalograhic and spectral patterns.…”

“…Of relevance to this report, direct reciprocal thalamocortical projections have been implicated in generation of sleep rhythms in mammals (6). These projections are not known in birds, but recent studies have identified descending recurrent projections of sensory pathways in birds that might serve similar functional roles, for example in the auditory system (10, 11).Both REM and NREM are known for birds, with sleep in most species being dominated by NREM with brief REM episodes (12), although passerine birds exhibit greater amounts of REM (13,14). Circadian patterns in REM and NREM are commonly known in birds (15), and there is also fragmentary evidence regarding other characteristics (16).…”

“…Both REM and NREM are known for birds, with sleep in most species being dominated by NREM with brief REM episodes (12), although passerine birds exhibit greater amounts of REM (13,14). Circadian patterns in REM and NREM are commonly known in birds (15), and there is also fragmentary evidence regarding other characteristics (16).…”

Most sleep does not serve a vital function. Evidence from Drosophila melanogaster

“…We know that some species -such as elephants (16) or giraffes (17) -have evolved to cope with limited amount of sleep and several genetic mutations conferring short sleeping phenotypes in flies, rodents, and humans have been characterised in the past two decades (reviewed in (18)); some animals are also able to forego sleep for days or weeks in particular ecological conditions (16,(19)(20)(21), but the identification of a constantly sleepless animal can be considered a holy grail of the field.…”