A Little Bit More
The arrival of Robins is often considered the beginning of spring for many people but as the unit poster points out, some robins never left in the first place! Those robins (American Robin, if we use the full name) living in Canada and extreme northern U.S. do migrate south for the winter but in most of the U.S., at least some robins stay behind for the winter months.
There are two main problems facing the stay-behind robins in the north: cold temperatures and a reduced food supply. To cope with the cold, robins are able to reduce their energy needs by lowering their nighttime body temperatures from a normal 41°C (105°F) to 39°C (103°F). This may not seem like much but every little bit of energy conservation helps.
But they still need enough food to stoke their “furnace”. A bird’s secret to a normal daytime body temperature is to eat enough food to maintain its fat reserves. During especially low winter temperatures, it appears to be more important for a bird to have an adequate energy source, food or energy reserves from food, for providing heat than it is to have adequate insulation, good feather insulation, for preventing heat loss. In other words, the real threat to a bird in winter is not freezing – but starving!
During winter, robins feed mainly on wild fruits that are high in energy. It’s also interesting to note that they’re selective in which fruits they choose – those highest in caloric value are preferred. These fruits allow winter robins to maintain a high glucose level in their blood that is about double that of humans, and this is adequate to fuel their high metabolic rate.
Activities
Science & Geography – Winter Robins
Objectives: Better understanding of how range maps work in field guides
Materials: Access to web or field guide to North American birds
Field guides are extremely useful reference sources and are used by biologists and the public all the time. Since many birds migrate and are not found in the same location at all times of the year, a field guide on birds reflects this in their range maps. These maps show where the bird in question nests, where it winters, and where these two may overlap. We’ve just learned from the unit that the American Robin has two “strategies” during the winter and may or may not migrate, depending on its location and other factors. Let’s look at the range map for the American Robin and see what we can learn from this visual information.
If your students have read the unit poster and “A Little Bit More”, they’ll have no trouble answering these questions but I think it’s still worth having them do the activity to reinforce how range maps work.
Have your students either access this website or go to a field guide on birds in North America and look at the American Robin’s range map. An excellent field guide choice is “A Field Guide to the Birds East of the Rockies” or “Western Birds” both by Roger Tory Peterson and available at most bookstores or online at the Peterson Institute (www.rtpi.org)
Make sure students understand that the range map shows the nesting area (one color), the wintering area (one color) and the overlap (combination of the two colors). So, at a glance, they should be able to understand where robins nest, winter, or both. Looking at the range map, students should be able to answer the following:
- Does the American Robin nest in “your” state/province? Answer will depend on your personal location
- Does the American Robin winter in “your” state/province? Answer will depend on your personal location
- Are there areas in your state/province where the American Robins nest but do NOT winter? Answer will vary depending on where you live
- We can see from the range map that American Robins do spend the winter in some cold, northern areas of the continent. So why are there areas in North America where no American Robins spend the winter? Areas where the robins do NOT spend the winter are either too cold and/or there is not enough food during the winter months to support them.
Range map for American Robin
Key Concepts
Behavior and Regulation, Populations and Ecosystems
Questions
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