Arctic summers mean migrating animals, a bounty of breeding opportunities, and 24 hours of sunlight. Many plants and animals experience 24-hour cycles telling them when it’s time to rest and when it’s time to get up—called the circadian rhythm—that are often tied to light cues. So what happens when the sun never sets?
For four species of migrating birds that breed in the Arctic, new research shows that “anything goes,” said Bart Kempenaers, a behavioral ecologist with the Max Planck Institute for Ornithology near Munich. Lapland longspurs (Calcarius lapponicus) exhibit a 24-hour cycle, while semipalmated sandpipers (Calidris pusilla) and pectoral sandpipers (Calidris melanotos) are active around the clock. Red phalaropes (Phalaropus fulicarius) shift from a roughly 21-hour cycle to a 29-hour cycle. The type of cycle each displays depends on the species, an individual’s sex, and their social circumstances….
In contrast, the Lapland longspur—also a one-ounce (30-gram) bird, where both parents incubate the eggs—kept to a 24-hour activity cycle. Both the males and females rested between midnight and four in the morning.
But for pectoral sandpipers and red phalaropes, where just one parent incubates the egg, only the caregiver stayed on a 24-hour cycle. The promiscuous members of these two species—male pectoral sandpipers and female red phalaropes—were active around the clock.
There is a lot of pressure on male pectoral sandpipers to mate with as many females as they can, Kempenaers said. A study he published with colleagues last year in the journal Science found that the more active male pectoral sandpipers sired more offspring. Since female red phalaropes are the ones competing for mates, he explained, “you see this constant activity, or arrhythmic pattern, in the females.”
This one-sided, round-the-clock activity seems to be related to sexual selection, Kempenaers said, rather than to feeding—as speculated for Arctic residents like reindeer or ptarmigan.
(Read more at National Geographic)
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