Cows and Calves and Ice, Oh My!
Looking for Correlations

Biologist Wayne Perryman is the government's leading authority on gray whale calf production. When Mr. Perryman saw interesting fluctuations in numbers of calves born each year since he started counting in 1994, he knew it was a result of some factor. What might cause it? He noted other significant events during this period, including these:

  • High numbers of whales died in strandings in 1999 and 2000, and many whales were thin and undernourished.
  • Calf births hit an alarming low during his study years.
  • Scientists did not see a large number of dead calves in the lagoons or along the beaches, as they would if the babies were being born and then died for some other reason.
  • Especially in 1999 and 2000, some whales appeared skinnier than normal.
  • The Bering and Chukchi seas saw abnormally heavy seasonal ice in the early years of the study, while in more recent years ice melt has been later.
Number of Northbound Newborns
(as of end-of-season counts):



















Scientists look for correlations between variables. Mr. Perryman wondered: Do gray whales have access to their food over the same amount of time every year? (Or, How long was their feeding ground ice-free?) He wrote a scientific paper that looked at how skinny whales may be linked to low calf production and ice conditions from 1997 to 2002. Mr. Perryman concedes that many pieces need to be studied before the puzzle is solved. This is your chance to think like a scientist as you look at a bit of Mr. Perryman's research.

Try This! Journaling or Discussion Questions
  • What two variables are the scientists investigating, as shown on this graph?
  • Do you ever see a year with a long feeding season and a low of number of calves? Do you see a short feeding season followed by a high number of calves? What hypothesis might you pose?
  • Does this graph seem to show any correlations? Explain your thinking.
  • Where might a dot on the graph show up if these variables were NOT correlated? Can you suggest (1) a number of calves and (2) a length of feeding season that would NOT fit the pattern that Wayne Perryman has found so far?

For More:

See Photogrammetry: A Way to Study Whales. Examine photos that help Wayne Perryman learn more about the condition of gray whales.

National Science Education Standards

  • Use data to conduct a reasonable explanation.
  • Think critically and logically to make relationship between evidence and explanations.
  • Science investigations involve asking and answering a question and comparing that to what scientists already know about the world.
  • Scientists develop explanations using observations (evidence) and what they already know about the world.