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Inactivity/sleep in two wild free-roaming African elephant matriarchs – Does large body size make elephants the shortest mammalian sleepers?

View Article: PubMed Central - PubMed

ABSTRACT

The current study provides details of sleep (or inactivity) in two wild, free-roaming African elephant matriarchs studied in their natural habitat with remote monitoring using an actiwatch subcutaneously implanted in the trunk, a standard elephant collar equipped with a GPS system and gyroscope, and a portable weather station. We found that these two elephants were polyphasic sleepers, had an average daily total sleep time of 2 h, mostly between 02:00 and 06:00, and displayed the shortest daily sleep time of any mammal recorded to date. Moreover, these two elephants exhibited both standing and recumbent sleep, but only exhibited recumbent sleep every third or fourth day, potentially limiting their ability to enter REM sleep on a daily basis. In addition, we observed on five occasions that the elephants went without sleep for up to 46 h and traversed around 30 km in 10 h, possibly due to disturbances such as potential predation or poaching events, or a bull elephant in musth. They exhibited no form of sleep rebound following a night without sleep. Environmental conditions, especially ambient air temperature and relative humidity, analysed as wet-bulb globe temperature, reliably predict sleep onset and offset times. The elephants selected novel sleep sites each night and the amount of activity between sleep periods did not affect the amount of sleep. A number of similarities and differences to studies of elephant sleep in captivity are noted, and specific factors shaping sleep architecture in elephants, on various temporal scales, are discussed.

No MeSH data available.


Sleep times and trunk activity.                        Scatterplots showing the lack of a relationship between total trunk                            activity between main sleep episodes and total sleep time                                (TST, hours, h) (A) or                            duration of the main sleep episode (hours, h)                                (B) for both Matriarch 1 (closed circles)                            and Matriarch 2 (open squares). While there is a trend for                            shorter sleep times with increased trunk activity, these trends are not                            statistically significant even when the days without sleep are removed                            from the analysis. These plots demonstrate that prior activity does not                            appear to affect sleep times.
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pone.0171903.g009: Sleep times and trunk activity. Scatterplots showing the lack of a relationship between total trunk activity between main sleep episodes and total sleep time (TST, hours, h) (A) or duration of the main sleep episode (hours, h) (B) for both Matriarch 1 (closed circles) and Matriarch 2 (open squares). While there is a trend for shorter sleep times with increased trunk activity, these trends are not statistically significant even when the days without sleep are removed from the analysis. These plots demonstrate that prior activity does not appear to affect sleep times.

Mentions: In order to assess whether the level of activity prior to sleep influenced the duration of sleep, we examined the distance travelled between main sleep episodes and the counts of trunks movements between main sleep episodes, with the subsequent length of the main sleep episode and the associated total daily sleep time. No correlation between the distance traversed between main sleep episodes and the total sleep time or the duration of the subsequent major sleep episode was observed (Fig 8). For Matriarch 1, the average distance traversed between major sleep episodes amounted to 16.1 km (s.d. = 13.2 km; range = 5.1–66.4 km) (Fig 9A), while for Matriarch 2 the average distance traversed was 17.3 km (s.d. = 9.9 km; range = 7.7–51.5 km) (Fig 8B). In both elephants a weak trend towards having a longer total sleep time or main sleep episode with a shorter distance traversed between main sleep episodes was apparent, but these trends were not statistically significant for either individual elephant or when the data from both elephants was combined. This lack of correlation was maintained when the days without sleep, leading to a greater distance and time between major sleep episodes, were excluded from the analysis.


Inactivity/sleep in two wild free-roaming African elephant matriarchs – Does large body size make elephants the shortest mammalian sleepers?
Sleep times and trunk activity.                        Scatterplots showing the lack of a relationship between total trunk                            activity between main sleep episodes and total sleep time                                (TST, hours, h) (A) or                            duration of the main sleep episode (hours, h)                                (B) for both Matriarch 1 (closed circles)                            and Matriarch 2 (open squares). While there is a trend for                            shorter sleep times with increased trunk activity, these trends are not                            statistically significant even when the days without sleep are removed                            from the analysis. These plots demonstrate that prior activity does not                            appear to affect sleep times.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382951&req=5

pone.0171903.g009: Sleep times and trunk activity. Scatterplots showing the lack of a relationship between total trunk activity between main sleep episodes and total sleep time (TST, hours, h) (A) or duration of the main sleep episode (hours, h) (B) for both Matriarch 1 (closed circles) and Matriarch 2 (open squares). While there is a trend for shorter sleep times with increased trunk activity, these trends are not statistically significant even when the days without sleep are removed from the analysis. These plots demonstrate that prior activity does not appear to affect sleep times.
Mentions: In order to assess whether the level of activity prior to sleep influenced the duration of sleep, we examined the distance travelled between main sleep episodes and the counts of trunks movements between main sleep episodes, with the subsequent length of the main sleep episode and the associated total daily sleep time. No correlation between the distance traversed between main sleep episodes and the total sleep time or the duration of the subsequent major sleep episode was observed (Fig 8). For Matriarch 1, the average distance traversed between major sleep episodes amounted to 16.1 km (s.d. = 13.2 km; range = 5.1–66.4 km) (Fig 9A), while for Matriarch 2 the average distance traversed was 17.3 km (s.d. = 9.9 km; range = 7.7–51.5 km) (Fig 8B). In both elephants a weak trend towards having a longer total sleep time or main sleep episode with a shorter distance traversed between main sleep episodes was apparent, but these trends were not statistically significant for either individual elephant or when the data from both elephants was combined. This lack of correlation was maintained when the days without sleep, leading to a greater distance and time between major sleep episodes, were excluded from the analysis.

View Article: PubMed Central - PubMed

ABSTRACT

The current study provides details of sleep (or inactivity) in two wild, free-roaming African elephant matriarchs studied in their natural habitat with remote monitoring using an actiwatch subcutaneously implanted in the trunk, a standard elephant collar equipped with a GPS system and gyroscope, and a portable weather station. We found that these two elephants were polyphasic sleepers, had an average daily total sleep time of 2 h, mostly between 02:00 and 06:00, and displayed the shortest daily sleep time of any mammal recorded to date. Moreover, these two elephants exhibited both standing and recumbent sleep, but only exhibited recumbent sleep every third or fourth day, potentially limiting their ability to enter REM sleep on a daily basis. In addition, we observed on five occasions that the elephants went without sleep for up to 46 h and traversed around 30 km in 10 h, possibly due to disturbances such as potential predation or poaching events, or a bull elephant in musth. They exhibited no form of sleep rebound following a night without sleep. Environmental conditions, especially ambient air temperature and relative humidity, analysed as wet-bulb globe temperature, reliably predict sleep onset and offset times. The elephants selected novel sleep sites each night and the amount of activity between sleep periods did not affect the amount of sleep. A number of similarities and differences to studies of elephant sleep in captivity are noted, and specific factors shaping sleep architecture in elephants, on various temporal scales, are discussed.

No MeSH data available.