Plasma melatonin in the Adelie penguin (Pygoscelis adeliae) under continuous daylight in Antarctica
Article first published online: 30 JAN 2007
Journal of Pineal Research
Volume 10, Issue 1, pages 2–8, January 1991
How to Cite
Cockrem, J.F. (1991), Plasma melatonin in the Adelie penguin (Pygoscelis adeliae) under continuous daylight in Antarctica. Journal of Pineal Research, 10: 2–8. doi: 10.1111/j.1600-079X.1991.tb00002.x
- Issue published online: 30 JAN 2007
- Article first published online: 30 JAN 2007
- Received May 21, 1990; accepted September 28, 1990
- Key words: melatonin — penguin — continuous light — Antarctica — light intensity
Cockrem JF, Plasma melatonin in the Adelie penguin (Pygoscelis adeliae) under continuous daylight in Antarctica. J. Pineal Res. 199 1 10:2-8.
Circadian rhythms of melatonin secretion in birds are influenced by daylength and light intensity. Daily patterns of melatonin secretion were examined in Adelie penguins (Pygoscelis adeliae) under natural continuous daylight at Cape Bird, Antarctica (77$S). Although daylight is continuous during the Antarctic summer there was a marked daily cycle of light intensity. However, there was no relationship between mean plasma melatonin levels and time of day in groups of 2–10 penguins sampled at 2–3 h intervals in November, December, or January. Mean melatonin levels over 24 h in groups of birds from which single samples were collected, or in groups of birds sampled repeatedly through cannulae, were low (12.4 ± 1.2 pg/ml-28.8 ± 4.4 pg/ml for 4 sampling periods; n = 22-163). Levels in individual birds were, however, quite variable and ranged from 5.0–68.1 pg/ml. Some birds had periods of increased melatonin levels that tended to occur during the time of day when light intensity was least. One bird had a clear low amplitude melatonin rhythm with a peak during the time of least light intensity. These results, the first for any bird under a natural photoperiod, indicate that melatonin secretion is inhibited by natural continuous daylight, but that it is not abolished.