Vectors

Vectors

Image from the Arctic Tern Migration Project (follow link for higher resolution image)

 

The map of the Arctic Tern migration (shown above) illustrates a migration route that is far from the shortest possible path.  Why would a animal choose this route?  It is clearly not random, as many animals take this route year after year.

Direction - why is the straight path not necessarily the “best”

  1. Brain storm session - Why would the birds travel that far?
  1. Looking for food?
  2. Lost?......
  1. Lets look at a map of prevailing winds from Prevailing Winds Wikipedia page
  1. Does this map help to explain the migration path?
  1. Wind directly impacts birds’ ability to cover distances. Like an escalator allows people at a shopping mall to go up and down while spending less energy, a favorable wind reduces the energy required for a bird to travel. The inverse is also true, where a head wind increases the energy need by a bird to travel. See image below.

  1. Vector addition - Wind speed is not necessarily in the same direction as the bird flight.

  1. The Arctic Tern travels south at an average rate of 330 kilometers per day, while it travels north at an average rate of 520 kilometers per day.  If we are to assume that the birds are in the air the whole time and that the different in speed is due to more favorable winds during the northward route, how much faster are the winds (in the direction of travel) during the northward migration? (Give answers in meters per second)
  1. Answer: Distance per day = average speed(m/s) x 3600(s/hour) x 24(hour/day) and speed = bird speed + wind speed vn is and vs is therefore the difference in wind speed is

    vn -vs = 6m/s - 3.8m/s = 2.2 m/s

Note:  The migration of the Arctic Tern poses some questions.

  1. Why is it that the Arctic Tern travels at a much faster rate during its northern migration then when it is going south?
  2. Wind speed likely plays a role, but what other things might slow down a bird or make it go faster?
  3. Availability of food in the Atlantic hot spot where they spend 25+ days on their way south is a factor, but what about things like competition among other Arctic Terns?
  4. What other questions can be posed by the information on the Arctic Tern Project website?