The 24 hours of summertime sunlight in Barrow, Alaska is enough to throw any person’s daily schedule into a tailspin. Trying to get a good night’s sleep in broad daylight is tricky enough, and keeping track of whether it’s day or night can be mind bending. But the Lapland Longspur (Calcarius lapponicus) doesn’t seem bothered by the fact the sun doesn’t set in Barrow during the summer. These tiny songbirds manage to keep their internal clock ticking perfectly.
Noah Ashley, a postdoctorate fellow at the University of Alaska Anchorage, has spent the last two summer field seasons in Barrow trying to determine exactly how the Lapland Longspur manages to regulate its behaviors and which external environmental cues they use to reset their circadian rhythms.
Circadian rhythms play a key role in how humans and animals time their behaviors—helping to regulate important daily functions like sleeping and eating. Normally, these rhythms are synchronized everyday by the light-dark patterns of the day and night. During the long periods of daylight or darkness in the Arctic, caribou and other birds like the Rock Ptarmigan will completely abandon their circadian rhythms. But the Lapland Longspur does just the opposite.
“When they’re in Alaska during the breeding season, these birds will actually exhibit a very distinct rhythm that other animals will abandon,” Ashley explained. “They will be active throughout the entire day. And then around subjective ‘midnight’ they’ll basically hunker down in the tundra and become quiescent until about 4:30 a.m. These birds are synchronizing their rhythms with some unknown environmental signal that other animals are not cueing in on.”
The Lapland Longspur’s very punctual behavior patterns piqued Ashley’s curiosity. He speculated that subtle changes in light intensity or slight variations to the color of the sunlight as the day progressed might actually be regulating the birds’ behavior. With funding from the National Science Foundation he put together a team and set out to unravel these little birds’ timely mystery.
Working on a Bird’s Schedule
The Lapland Longspur is the Arctic’s most abundant songbird. Every year, flocks of these birds set out from southern Canada and the northern United States to their Arctic breeding grounds where they will attract a mate and raise their young. They arrive in Barrow every year like clockwork around May 26 and stay until early September. The breeding season is short, leaving Ashley and his team little time to study the birds.
(Listen to the vocalizations of a male Lapland Longspur: LALO1)
Observing the behavioral rhythms of the birds is a 24-hour process. “In order to study circadian rhythms, you have to be a morning person, a late-night person and everything in between,” Ashley joked. Over the past two field seasons Ashley has trained four Alaskan native high school students and three University of Alaska undergraduate students to help with his fieldwork.
The team takes shifts observing the birds’ behaviors throughout the day and night, recording songs, and noting the location and number of nests tucked in the tundra grass.
They also capture the birds using baited walk-in traps called potter traps. Once the birds are captured, the researchers take detailed measurements, draw blood samples to quantify levels of melatonin (a hormone closely associated with circadian rhythm in animals), and band the birds for record keeping purposes before letting them go.
“The students really enjoyed catching birds, learning how to handle them, take measurements, weigh them, and let them go. It’s always nice to watch them fly off” Ashley said. “However, the one tradeoff of the internship was that students had to work weird hours,” he laughed.
In 2009 the team caught roughly 230 birds and in 2010 they caught about 130. Some of the birds were held in captivity for further study at the Barrow Science Center and then transferred to the University of Alaska Anchorage.
From the Field to the Lab
In the fall of 2009, Ashley closely observed forty-eight Lapland Longspurs in a lab setting where he could carefully regulate environmental conditions. During his tests, the birds were exposed to different light spectra and intensities, but he could not get them to sync their behaviors to these different treatments.
“This was a negative result. The birds actually weren’t able to cue into these small changes. So I went back to the drawing board and was thinking ‘hey, what other environmental factors could birds be responding to?’” Ashley said. He formulated several new ideas on what might control the birds’ daily rhythms that he hopes to test in the future.
One hypothesis is that the birds needed to be in breeding condition to synchronize their rhythms to small environmental changes. In the captive experiment, birds tested were in non-breeding condition and sex steroids, such as androgens and estrogens, are known to be very low during this time. Like most songbirds, Lapland Longspurs undergo dramatic changes in reproductive behavior and physiology during the breeding season and testosterone levels in males are elevated. Ashley speculates that longspurs might need to be in breeding condition to entrain to these small changes in light intensity or color. In conjunction with Brady Salli and Dr. Loren Buck at the Univ. of Alaska, he will test this idea in the fall by treating birds with sex steroids to examine if their sensitivity to light changes.
Diet may be another factor affecting the birds’ rhythmicity. During the breeding months on the tundra, the birds switch to a diet largely composed of mosquito larvae and crane flies. Ashley thinks it’s possible that the birds are cueing into the active periods of the insects, rather than changes in light. He also plans to determine if changes in ultraviolet light influence circadian rhythms.
Ashley hopes that learning more about the factors that control the Lapland Longspur’s very well tuned internal clock will shed light on how humans and other animals adapt to light and darkness conditions in Arctic latitudes. “I’ve always been interested in songbirds and I like being out late in the summer because the tundra mellows out and becomes really quiet and peaceful. This made me wonder what the birds were up to and I wanted to learn more.” Ashley said.—Alicia Clarke