Raptor numbers in Tahoe increase during winter
Tahoe Institute for Natural Science
Snow accumulation, holiday traffic, and lift lines aren’t the only things that increase during a Tahoe winter… you may also notice a surge in Bald Eagle numbers as they migrate into the Tahoe Basin in pursuit of reliable prey.
But why? Although you can find a Bald Eagle in Tahoe at any point during the calendar year, whether it is stealing a fish from a rival Osprey in the summer, or guzzling down a Kokanee Salmon near the mouth of Taylor Creek in the fall, Bald Eagles and other raptors increase in numbers during the winter months for a variety of reasons.
Bald Eagles eat an array of fleshy things including fish, small mammals, roadkill, and in Lake Tahoe especially, waterfowl such as ducks, grebes, and coots. Because of Lake Tahoe’s size and depth, it doesn’t freeze. This allows an assortment of migrant waterfowl to congregate “safely” in open water where they can find food in the shallows throughout the winter. However, when prey congregate, their predators eventually find them, making Tahoe and the surrounding valleys exceptional locations to watch Bald Eagles in the December, January, and February months.
Other raptors visit Tahoe’s meadows and surrounding valleys, like Ferruginous Hawks from open country elsewhere in North America’s west and Rough-legged Hawks from the Arctic, in search of rodents found in the agricultural fields of Carson and Sierra valleys. Of course more typical Sierra raptors like Red-tailed Hawks, Northern Harriers, and Prairie Falcons join in as they hunt for voles and other rodents dispersed in the fields.
Later in the winter, the Bald Eagles that aren’t chowing down on the waterfowl at Lake Tahoe will concentrate with other raptors (and Golden Eagles) in these same surrounding valleys as they opportunistically feed on afterbirth and stillborns as a byproduct of winter calving season.
The prevalence of our triumphant eagle around Tahoe hasn’t always been the case. Shortly after the Bald Eagle became the U.S.’ national symbol in 1782, the glorious bird’s populations began to plummet. Poisoning and persecution (most raptors were shot on sight in earlier times) led to massive declines of our precious raptor, and eventually the widespread use of an insecticide called DDT in agriculture nearly finished them off, as the dangerous chemical contaminated nearly every food web in the Red, White, and Blue.
By the 1960s, there were only 487 nesting pairs of bald eagles remaining in the United States.
Fast forwarding to the good news, DDT in the U.S. was banned from use in 1972 and protective measures were put in place on Bald Eagles. Soon populations began to rise – including in Tahoe, thanks to data collected by government agencies and the Tahoe Institute for Natural Science (TINS).
Every year, the TINS leads a group of volunteers to count Bald Eagles during the second Friday in January, in an event known as the Mid-Winter Bald Eagle Count, part of a national effort to census eagle populations across the country. In the early 1980s, when the Tahoe count began, there may have been only one or two sightings of Bald Eagles per year.
In 2021, TINS generated a tally of 42 total Bald Eagles.
This dramatic increase in eagle numbers reflects a continent-wide trend, carefully documented at Tahoe thanks to careful, expert data analysis by TINS staff and the efforts of many hundreds of volunteers over the years. This story not only presents an impressive population rebound, but also highlights the environmental consequences to our actions and underlines the importance of tracking population status.
TINS has the privilege to be a part of Bald Eagle research and you could be too. Please join us for our 43rd annual Mid- Winter Bald Eagle Count occurring on Jan. 14. 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 virtual webinar about Bald Eagles, their ecology and populations, and how to age individuals (tell them apart). Did you know that Bald Eagles don’t acquire a fully white head and tail until they are at least five years old? Join the webinar to learn more about these impressive birds.
If you would like to learn more about Tahoe’s natural history, learn more about wintering raptors, join the Tahoe Institute for Natural Science on one of our many free nature tours, open to nature enthusiasts of all experience levels. To learn more, visit us at http://www.tinsweb.org.
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