Calculating the Mean
Average Rubythroat First Arrival Dates

1 - 2 periods


Your enthusiastic students are probably wondering, "When will our hummingbirds return?" For many years, Journey North has collected first arrival data from observers across North America. Your young scientists can use these historic records — and their math skills — to figure out the mean (average) arrival dates over a span of years. This can help them make predictions about when they'll see these tiny pollinators this year.

Laying the Groundwork
Ask students, When do you think we'll see the first hummingbirds this year? As students suggest dates ask, What's your reasoning? What factors do you think might influence when they show up? How could we make a prediction that's based on real data? If it doesn't come up, let students know that Journey North has records of when hummingbirds were first sighted in different locations for the past 8 years.


  1. Before digging into Journey North's archived records of first hummingbird sightings, you may want to have students practice calculating mean (average) arrival dates in one location by using data from Lanny Chambers, a Journey North observer in St. Louis, MO.

    Hand out the Calculating the Mean student worksheet. If your students have the math skills to complete the exercise, you can simply give them the list of "dates of first sighting" from Lanny's data (see Calculating the Mean: Sample). If they need more support, hand out the Calculating the Mean: Sample and work through it together.

  2. Invite students to look at sample data from your state or town. Have they collected hummingbird arrival data from year to year or do they know someone who has? If not, pull up Journey North's Archives of sightings. They can use the dropdown boxes in the lefthand column to view first sightings of rufous and ruby-throated hummingbirds each month from 1997 to the present. As students work in small groups to review the data for their state, ask the following questions, as appropriate:
Predicting When Hummingbirds Will Return
  • What can you tell from a first glance at the data? (For instance, "Hummers were reported arriving in the north from March-May," "The last three years, they first showed up in our state in April," "Their arrival dates change from year to year," and so on.) What questions do you have? How might we find answers?

  • How can the data help us predict when they might arrive this year? Let students pursue some of their ideas or suggest using the Calculating the Mean student worksheet.

  • What factors might influence when hummingbirds arrive in our area? If students suggest weather as a factor, challenge them to compare weather maps from this year or previous years with the hummers' patterns of arrival. This Graphic Weather Archive features average temperatures, precipitation, temperature departure from normal, and other data each month from 1999-2005.

  • Do you think the hummers will be early or late this year? Explain your thinking. (Consider having students predict first arrival dates individually or as a class. This just might motivate your eagle-eyed observers to pay close attention in the schoolyard and neighborhood!)

  Making Connections — Journaling and Discussion Questions

  • What factors do you think affected when the hummers arrived this year?
  • Which of these do you think influenced hummingbirds directly (e.g., storms) and which influence them indirectly (e.g., temperatures might affect availability of nectar and insect food sources).
  • List all the factors that might cause the data from observers to be different from year to year. (Review the lesson, You're the Scientist: Verifying Data Collected by Peers.)
  • What general conclusions can you draw about hummingbirds' arrival in their breeding grounds?
  • Why do you think scientists value the practice of long-term record keeping? What types of things can they learn from doing this?