ARCTIC TERN MIGRATION

The question of ontogeny discusses how the trait is formed, and how the development is controlled by certain mechanisms.

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Some questions that we would like to ask include:

Would an arctic tern migrate without a social or parental influence? How does group decision affect a tern’s decision to migrate seasonally? If a tern switches flocks during the migration, will it follow the migration pattern of the other flock? 

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    One study done by Moller and Mardal investigated the question of whether the change in the timing of the annual migration cycle was a consequence of arctic terns adapting to climate change. They wanted to find out if the time when terns began their migration was a learned behavior, and if they could alter their cycle and breeding times based on the climate. This was seen as an important question, because delaying the start of migration could affect the timing of the rest of the cycle.

    Using pre-collected data of breeding dates of the past 70 years, and records of the mean temperature and total precipitation for April-May in Denmark and in the Souther Ocean, they discovered that over time, the mean breeding date has advanced by almost three weeks. They also used information on the amount of fertilizer in agriculture and the amount of shrimp, which have been seen to influence the breeding of terns. 

    They found that terns were able to adapt to the gradually changing climactic conditions and resource availability each year by learning from year to year, and adjusting their travel date correspondingly. This correlation between the arrival/breeding dates and the climate suggest that the time that terns begin to migrate is developed through learning. 

 

Source:

Mollder, Flensted-Jensen, Mardal. Adjustment of the annual cycle to climatic change in a long-lived migratory bird species. Current Zoology, 55(2): 92-101, 2009. 

 

 

    A study done by Wiltschko et al on how birds navigate when far from home suggests that birds rely on compass mechanisms. They are able to rely on the intensity of the magnetic field of the earth, as well as the sun. Although this study did not focus specifically on terns, it allows one to see the types of inherited methods of navigation that many birds use. Because terns have such a long migration, knowing that their sense of direction is genetic and passed down through generations allows one to gain insight into the ontogeny of migration. 

    Wiltchisko et al manipulated the magnetic field around the cage with Helmholtz coils to determine the effects on the birds. Following the shift in the magnetic fields, the birds showed an inclination to fly “north”, which was really southeast. They are also able to use the sun as a compass, depending on which region they are flying through. As a tern migrates from the northern to the southern hemisphere, being aware of the different angles of the sun is extremely important. 

 

Roswitha Wiltschko, Wolfgang Wiltschko, Avian Navigation. The American Ornithologists’ Union, 126(4): 717-743.