Bald eagles of Lake Tahoe: A story of triumph
January 9, 2019
Soaring through the sky, a pair of bald eagles is searching for their next meal.
As snow covers the mountains around Lake Tahoe, the eagles are in pursuit of waterfowl that have migrated from the north to spend their winter in Tahoe's unfrozen waters. One of these eagles has a full white head and tail, but the other bald eagle is almost all brown and black.
This is because a bald eagle does not fully acquire its adult plumage until it reaches its fifth year. With a six to nearly eight-foot long wing span, strong talons and massive, sharp beak, a bald eagle spotted hunting from the sky puts most people in a state of awe.
Although many people have been able to catch sightings of America's symbol in the Tahoe region in recent years, it hasn't always been this way. Today, if you spent the day looking for bald eagles in the appropriate habitat around Lake Tahoe, there would be a very high chance you would spot one, or even a few different individuals.
Now, if you were to rewind to the 1980s, or especially a few decades prior, it would be a rare sighting to find an eagle in the sky.
Every year, the Tahoe Institute for Natural Science (TINS) leads a group of volunteers to count bald eagles during the second Friday in January, known as the Mid-Winter Bald Eagle Count, part of a national effort to census eagle populations across the country.
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In early 1980s, when the Tahoe count began, there may have been only one or two sightings of bald eagles per year. In 2017, TINS generated a tally of 27 total Bald Eagles, despite the challenging conditions of a three-hour count on a cold, post-storm morning.
Has Tahoe's wintering eagle population changed that dramatically? Yes.
When America adopted the bald eagle as the national symbol in 1782, the country may have had as many as 100,000 nesting eagles. Soon after, this species began to decline in population due to loss of habitat and outright persecution through poisoning and poaching. Many believed they were a threat to livestock as well as a competitor for game.
In 1940, noticing that the species was "threatened with extinction," Congress passed the Bald Eagle Protection Act, which prohibited killing, selling and possessing the species.
However, five years after eagles were formally protected, the insecticide DDT became available in the United States, and eagle populations plummeted even further. DDT is effective for a wide variety of insect pests, and its use spread quickly, subsequently poisoning the nation's waterways and contaminating every food web.
As a water-soluble organochlorine that persists up the food chain, DDT concentrations can become quite high in top predators. This became extremely problematic for bald eagles, peregrine falcons and other raptors, as one of the effects of DDT on birds is eggshell thinning.
In large birds such as bald eagles, the eggs require a relatively thick shell to support the weight of incubation, but with DDT poisoning, the shells were so thin that they often broke during incubation or otherwise failed to hatch.
By 1963, there were only 487 nesting pairs of bald eagles remaining in the U.S. DDT was banned from use in 1972, and shortly thereafter populations began to rise. In recent years, these protections have resulted in a dramatic rise in California and Nevada populations, one that is well demonstrated by the Tahoe count.
This story not only presents an impressive population rebound but underlines the importance of tracking population status and highlights the environmental consequences to our actions.
TINS has the privilege to be a part of bald eagle research and you could be too. Please join us for our 41st annual Mid- Winter Bald Eagle Count occurring on Jan. 11. Anyone and everyone is invited to help us count eagles. No experience is required, as we will pair you with someone who has done the count before.
In addition, the night before the count, we will host a potluck dinner for those who would like to learn more about bald eagles, their ecology and populations, and how to age individuals (tell them apart).
If you would like to register, email Sarah Hockensmith at firstname.lastname@example.org or give her a call at 775-298-0067. We certainly hope to see you there.
If you would like to learn more about Tahoe's natural history, come explore with the Tahoe Institute for Natural Science by joining us on one of our many free nature tours. All tours are free and open to nature enthusiasts of all experience levels. To learn more, visit us at http://www.tinsweb.org.