Effect of polar day on plasma profiles of melatonin, testosterone, and estradiol in high-arctic Lapland Longspurs

Michaela Hau, L. Michael Romero, Jeff D. Brawn, Thomas J. Van't Hof

Research output: Contribution to journalArticlepeer-review


In polar habitats, continuous daylight (polar day) can prevail for many weeks or months around the summer solstice. In the laboratory, continuous light conditions impair or disrupt circadian rhythms in many animals. To determine whether circadian rhythms are disrupted under natural polar day conditions in a species that is only a summer resident in polar regions we analyzed diet rhythms in plasma concentrations of metatonin, testosterone (T), and 17-β estradiol (E2) during the summer solstice in Arctic-breeding Lapland Longspurs (Calcarius lapponicus). We compared these profiles to those of conspecifics housed in outdoor aviaries at a mid-latitude site in Seattle, Washington, during spring, summer, fall, and winter. Under polar day conditions plasma melatonin concentrations of Lapland Longspurs were strongly suppressed, but still showed a significant diet rhythm. Likewise, plasma T in males, and E2 in females, showed significant diet changes in Arctic birds. Lapland Longspurs housed at mid-latitude in Seattle showed high-amplitude melatonin cycles at all times of the year, and the duration of the nightly melatonin secretion was positively correlated with the duration of the dark phase. We found no diel changes in plasma T in Seattle males in May, but Seattle females showed significant day/night differences in plasma E2 in May. The data suggest that even under polar day conditions diel rhythms can persist. The maintenance of hormone rhythms could provide a physiological basis to reports of rhythmic behavior in many birds during the Arctic summer.

Original languageEnglish (US)
Pages (from-to)101-112
Number of pages12
JournalGeneral and Comparative Endocrinology
Issue number1
StatePublished - 2002


  • Circadian system
  • Light suppression
  • Melatonin
  • Polar summer
  • Steroid hormone

ASJC Scopus subject areas

  • Animal Science and Zoology
  • Endocrinology

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