Unraveling the Mystery of Monarch Migration

monarch butterflies

Monarch butterflies fly between 50 and 100 miles each day during their migration. (Photo credit: Didier Dorval / Radius Images)

The monarch butterfly is the only butterfly species that makes an annual round-trip migration. Scientists have wondered for quite some time what triggers the monarch’s migration behavior. New research may finally provide an answer to that question.

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A Whale of a Tale

Humpback whales migrate seasonally from their feeding grounds to their breeding grounds. (Photo credit: NOAA)

People typically use Flickr to upload photos to share images of people, places, and events with their friends and family. A recent upload led to an amazing scientific discovery–a photo of a humpback whales fluke, or tail, taken during a whale sightseeing cruise 10 years earlier placed a humpback whale 9,800 km (6,000 miles) from where it had first been sighted by research scientists–a figure 3,200 km (2,000 miles) beyond the average whales yearly migration.

Marian C. Neves, a whale researcher associated with Brazil’s Instituto Baleia Jubarte, first spotted this particular humpback whale on August 7, 1999 off the coast of Brazil. At that time, scientists took skin samples from the whale and genetic analyses of the samples indicated that the whale, identified as whale 1363, was a female. On September 21, 2001, Freddy Johansen, a tourist from Norway, photographed the fluke of the same whale during a whale sightseeing cruise off the east coast of Madagascar. He didn’t upload the images from his trip until 2009, when he decided to back up photographs from his trip and share them with friends.

Gale McCullough, a research associate with Allied Whale, the College of the Atlantic’s marine mammal research group, works as a liaison with Flickr and searches the site for humpback whale images. She was the first to discover Johansen’s whale fluke photograph and identify it as a possible match to whale 1363. Each humpback whale fluke has a distinct pattern of speckles, and can be used to identify individual humpback whales, in the same way that fingerprints can be used to identify individual humans.

The uniqueness of whale fluke patterns was first discovered by College of the Atlantic researchers in the 1970s and quickly revolutionized the way scientists tracked and identified individual whales. For over 30 years, scientists have placed the data they have gathered (including identifying traits such as tail shape and color and underside patterns) on individual humpback whales into the Antarctic Humpback Whale Catalogue. Scientists across the world use this catalogue to study humpback whales and gather data on population sizes, migration patterns, sexual maturity, and behavior patterns.

Each humpback whale can be identified by its fluke, or tail, which has a unique shape and color pattern. (Photo credit: J. Waite, OAR/National Undersea Research Program (NURP); National Marine Mammal Lab/NOAA)

Each humpback whale can be identified by its fluke, or tail, which has a unique shape and color pattern. (Photo credit: J. Waite, OAR/National Undersea Research Program (NURP); National Marine Mammal Lab/NOAA)

Most humpback whales migrate twice-yearly. They spend their summers in temperate or polar waters where they feed on krill and then spend their winters in tropical waters where they mate and the females give birth to their calves. The whales follow the same route, which averages around 6,400 km (4,000 miles), year after year. What makes the distance traveled by whale 1363 extra unusual was that she was identified at two different breeding grounds.

Peter T. Stevick, lead author on a paper published about the humpback whale in the journal Biology Letters, offers two possible explanations for its wayward journey. One possible explanation is that the whale was exploring new habitat. A second explanation is that the whale simply got lost. For example, it might have gotten off course while tracking prey or looking for new feeding sites.

According to the Biology Letters article, the shortest possible distance between Brazil and Madagascar (with a route taking the whale from the South Atlantic Ocean to Africa and around to Madagascar in the Indian Ocean) is 9,800 km, which is 4,000 km longer than any previously-recorded movement between breeding grounds for a humpback whale. This distance is twice the species typical seasonal migratory distance and is the longest documented movement by a mammal.

Movement of an individual between breeding areas separated by approximately 90 longitudinal degrees, a continent, an ocean basin and nearly 10,000 km illustrates the ability of humpback whales to range across large portions of the globe, the authors explain in the article. Whatever factors resulted in this rare event, such extensive movement by an individual of a species that is typically philopatric [that is, returns to its place of birth] shows the extent of behavioral flexibility in movement that may be demonstrated within a species.

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Scientists Begin to Unravel Mystery of Marine Animals’ Migration

Hatchling loggerhead turtles, such as this one, imprint on the magnetic field of their birthplace. (Photo credit: Ken Lohmann, University of North Carolina at Chapel Hill)

Scientists at the University of North Carolina-Chapel Hill are working to unravel the mystery of how (and why) some marine animals return to where they were born to reproduce. For example, some salmon migrate over 1000 miles from the ocean upriver to their spawning grounds. Young loggerhead turtles from the North Atlantic migrate over 9000 miles before returning to the North American coast to reproduce.

Dr. Kenneth Lohmann, a professor of biology in the College of Arts and Sciences, and his team of researchers theorize that marine animals imprint on the magnetic field of the home area where they are born, and use differences in Earth’s magnetic field to return to their birthplace when it comes time to reproduce. Earth’s magnetic field differs across the globe, meaning that different areas of Earth have a different magnetic “fingerprint.” In addition, different regions of the ocean have slightly different magnetic fields, which allows migrating marine animals to home in on their place of birth.

Scientists think that learning more about how and when marine animals imprint on Earth’s magnetic field will help in future conservation projects. For example, scientists might be able to use knowledge of magnetic fields to direct sea turtles to protected areas, or re-establish salmon populations in rivers.

The full results of the scientists’ research are reported in latest edition of Proceedings of the National Academy of Sciences. Lohmann co-authored the paper along with UNC researchers Dr. Catherine Lohmann, a biology lecturer, and Nathan Putman, a graduate student in the biology department. The study was funded by the National Science Foundation.

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Bird Species Takes “Non-Stop Flight” to a Whole New Level

During their south-bound migration, bar-tailed godwits travel non-stop from their breeding grounds in Alaska to their winter grounds in New Zealand. (Illustration credit: USGS)

During their south-bound migration, bar-tailed godwits travel non-stop from their breeding grounds in Alaska to their winter grounds in New Zealand. (Illustration credit: USGS)

Bar-tailed godwits, a type of shorebird, have knocked the eastern curlew off its pedestal and taken over the title as non-stop migration champions. A team of researchers, led by Robert Gill, Jr., at the USGS Alaska Science Center based in Anchorage recently tracked a group of migrating bar-tailed godwits using satellite technology. A female bird referred to as E7 left the Alaskan breeding grounds and flew nonstop directly to its wintering grounds in New Zealand–a trip of over 11,680 kilometers. The flight took eight days, with no stops for food, water, or rest. E7’s flight is the longest direct flight ever recorded for a bird.

The researchers also tracked the flights of eight other females and two males. Seven of the females flew an average of 10,153 km over a period of (at most) 9.4 days. The two males’ flights were of a slightly shorter length, and took place over a period of (at most) 6.6 days.

The researchers monitored the birds’ flight using satellite transmissions. Female birds were implanted with a tiny satellite tracker. Males, which are smaller in size than females, were banded with lightweight external satellite trackers on their legs. Both males and females were also marked with a numbered leg band so that researchers could easily identify individuals in the field. The scientists followed the birds’ migration path in the air by monitoring the latitude and longitude coordinates the birds passed as they flew across the Pacific Ocean.

The southern migration of the bar-tailed godwit from Alaska to New Zealand is the longest known non-stop migration of any bird. On their north-bound return trip back to Alaska, the birds break their migration into two flights. First, they fly from New Zealand to the Yellow Sea in eastern Asia. After resting there, the birds continue their flight on to Alaska.

This female bar-tailed godwit was implanted with a satellite transmitter and given a leg band marked "E1" so that researchers could track its whereabouts in the air and in the field. (Photo credit: Jan van de Kam, NL/USGS)

This female bar-tailed godwit was implanted with a satellite transmitter and given a leg band marked “E1” so that researchers could track its whereabouts in the air and in the field. (Photo credit: Jan van de Kam, NL/USGS)

In studying the bar-tailed godwits’ southern-bound migration, the scientists also discovered that the birds time their migration with favorable tail winds that aid in their flight south. This discovery indicates the importance of weather patterns to the birds’ annual migration. Scientists worry that global climate change could disrupt this connection significantly.

While this study has answered some of the researchers’ questions about the migration of bar-tailed godwits with regard to distance and amount of time it takes, a number of mysteries remain. For example, the scientists wonder how the birds navigate, how they assess weather conditions, and at what altitude they fly. Further research will be necessary to answer these questions.

The full results of the scientists’ research are reported in the October 21st online edition of the Proceedings of the Royal Society B.

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