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Population Explosion!

Photo Courtesy of Ann Cook

Some ornithologists believe that red-winged blackbirds are the most abundant birds in North America. They spend the breeding season in marshes and wetlands with cattails--the more abundant the cattails, the more redwings can breed. And in the Dakotas, there are a LOT of cattails--about 750,000 acres of cattails in North Dakota alone. Most of these aren't native plants. They belong to a narrow-leafed variety that invaded the Dakotas in the 1940s, and their proliferation has contributed to the population explosion in redwings.

Just how many redwings are there? It's impossible to be precise, since there is no way someone can check every single place where they might be and count them all. Back in the winter of 1974-1975, scientists estimated that 190 million redwings were wintering in the U.S. Since then, redwings have declined in some areas where wetlands were filled, and increased in other areas where cattails have flourished in ponds. In North and South Dakota, the redwing population has increased about 33% from 1996 through 1999.

In any given year, about half of all redwings die. So how can their overall population increase so dramatically? Females usually start breeding their second year, and each female produces about 3-5 eggs, which they raise with the help of their mate. That keeps the males VERY busy, because each male who succeeds in obtaining a territory mates mates with 2-6 females, and sometimes even more! If a nest fails, females will often renest the same season. Overall, one study found that females produce a maximum of 24 surviving babies during their lives, and one male produced 176 fledglings on his territory. That's a lot of new red-winged blackbirds!

One thing that has helped them is the increase in cattails that are growing in Dakota wetlands. The cattails are actually not a native variety, and as their population has exploded, the redwings that nest in them have increased to fill the added habitat.

As beautiful and exciting as redwings are when they return to their marshes in spring, they cause problems for farmers, especially when their population gets very high. In 2001, the U.S. Department of Agriculture proposed a program to poison 6 million redwings. The U.S. Fish and Wildlife Service refused to grant the proposal, but farmers are having trouble trying to figure out how to deal with the overabundance of red-wings. To learn more, see our Red-wing Poisoning Lesson.


Try This! Journaling and Discussion Questions
  • In some areas people think deer or geese populations are too high. Can you think of any other animals that people consider overpopulated?
  • Chickadees and cardinals are two very common animals that people don't consider overpopulated. Can you think of any other abundant animals that are not considered too abundant?
  • What are some differences between the two lists of species? What makes us more comfortable with millions of chickadees than millions of redwings?
  • When scientists decide an animal population is too high, what should we do about it?

 
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