Bald Eagles

Last weekend, I had a thrill.  I saw a Bald Eagle flying over my neighborhood near Boulder, and then later in the day, I saw a Bald Eagle about 40 miles away, out by the Denver airport.  What a joy to see!  They are such beautiful and striking birds, with their stunning white head and tail.  I’ve always felt happy when I see them – not only because they are our national bird in the United States – but also because it reminds me that when we use science to understand what is happening in our environment, and make wise decisions based on this understanding, good things can happen.

I remember, when I was in my teens, the unanticipated impact of the widespread use of the pesticide DDT on the calcium metabolism of birds resulted in birds unable to lay healthy eggs, or birds going sterile.  Eggs couldn’t hold the weight of a full grown bird, to incubate them.  This, plus widespread habitat loss and hunting resulting in a dramatic drop in the number of Bald Eagles.  From an early 18th century population estimated between 300,000 and 500,000 birds, only about 400 mating pairs remained in the lower 48 states by the 1950s.

In 1962, biologist Rachel Carson documented the impact of DDT and other pesticides, and – among other things – their impact on bird populations.  As a result of research on this issue, and the work of federal science agencies and environmental groups, Bald Eagles were put on the Endangered Species List in the US in 1967, and in 1972 the use of DDT was banned in the US.  With these regulations in place, the population of Bald Eagles rebounded quickly, with an estimated total population of 100,000 birds in 1980.  Bald Eagles were removed from the Endangered Species List in 1995, and were removed from the US List of Endangered and Threatened Wildlife in 2007.  Bald Eagle sitings are now relatively common in the lower 48 states.

To me, this is one of the classic examples of how we can use our scientific knowledge, and our understanding of how the Earth system works, to solve problems in society.  Another example is the observed decline in atmospheric chlorofluorocarbon (CFC) levels (~10% since the peak in 1994), as a result of intense research and scientific consensus on the critical role of these compounds in the formation of the Ozone Hole, leading to international agreement to the Montreal Protocol in 1989.  Unfortunately, due to the long residence time of CFCs in the atmosphere and their strong catalytic action (each chlorine atom from CFCs can lead to the break up of tens of thousands of ozone molecules before it is removed from the atmosphere), it will still be decades before the Ozone Hole in the Antarctic is reduced significantly, and ozone levels recover elsewhere.  But we are clearly on the right track, and we are on this track because we agreed on societal action, through policy, based on scientific research and an understanding of the Earth system.

As we approach Earth Day in April, these and other examples of how we can come together and successfully address problems in our environment based on science may be useful to Earth science educators.

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