Bald Eagles Thriving and Maintaining Island Balance for Island Foxes

Across the Channel Islands, 2019 has been the best year for bald eagle reproduction since recovery efforts began 35 years ago. This spring 24 bald eagle chicks successfully fledged from nests. (That means they survived to fly.)

According to a press release from Channel Islands National Park: "This year there were 19 breeding bald eagle pairs on the Channel Islands producing 24 chicks, including 10 on Santa Cruz Island, 9 on Santa Catalina Island, two each on Anacapa and San Clemente Islands, and one on Santa Rosa Island."

Orange wing-tags mark Catalina-hatched bald eagles

Bald eagles are a vital part of the Channel Island ecosystem. As fishing eagles, they prey primarily on fish and other birds, as well as consuming carrion. Bald eagles do not typically eat mammal prey and therefore are not usually a threat to island foxes.

On occasion island foxes climb up into bald eagle nests. For the most part the foxes act as a clean-up crew picking up tidbits of food left behind by eagle chicks. Eaglets are typically either protected by a parent when very young or too large for island foxes to prey upon.

blue wing-tags mark no. island eagles

Bald eagles therefore help transfer vital nutrients from the marine environment up onto the island. They help provide marine resources to island foxes, deer mice, and the island ecosystem. Nitrogen and calcium from fish are dropped on the land or eaten and deposited via scat. Marine resources can then help to fertilize island plants.  

Island foxes and bald eagles lived in balance on the Channel Islands for thousands of years. The oldest bald eagle fossils found in Southern California are 35,000 yrs old and from the La Brea Tar Pits. Bald eagles declined between 1945 and 1960 because of the insecticide DDT which had been introduced by people into the surrounding marine environment. DDT and bald eagle.

Bald eagles historically kept golden eagles from colonizing the Channel Islands and, in doing so, protected the island fox. Though they are both called "eagles," bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) are not closely related. They come from two distinct evolutionary branches of predatory birds that separated and became competitors more than 12 million years ago. (By comparison, humans and chimpanzees diverged from a common ancestor just 7 million years ago.)

Golden eagles are mammal predators; they specialize in hunting small mammals about the size of a football (rabbits, ground squirrels, deer fawns, marmot, etc.) . Golden eagles hunt island foxes. They also eat carrion. Because both species will eat something that is already dead, they are known to take food from each other. There have been accounts of a bald eagle taking a dead island fox body from a golden eagle.


These two large birds have evolved to specialize in different food, but they compete for territory and nesting sites. Around the world fishing eagles and mammal-eating eagles are in competition with each other. You might think of them like dogs and cats–they share an ancestor, both are predators, but they have different specializations. They put up with each other at times, they will steal food from each, and in a confined space, like the islands, they just don't get along.

Though both bald and golden eagles are similar in size, resident bald eagles on the islands are frequently in mated pairs. Golden eagles encountering the islands are typically migrating individuals. This two-on-one situation gives bald eagles the upper hand.

When the Channel Islands' bald eagle population is thriving, there is no room for golden eagles and the habitat is safer for island foxes. Check out live bald eagle nest cams on the islands: http://www.iws.org/livecams.html

More Connections Between Bald Eagles and Island Foxes

courtesy of P. Sharpe; bald eagle catching fish off the islands

The recovery of bald eagles on the California Channel Islands has played an important role in island fox recovery. Bald eagles prey on fish and marine birds. They are not mammal predators and do not actively hunt island foxes. Because bald eagles nest on the Channel Islands, they chase away migrating golden eagles and do not allow them to colonize the islands.

With 50-60 bald eagles now living across the eight Channel Islands, no island foxes are known to have been killed by golden eagles for several years. Bald eagles definitely make a difference in the ecosystem for island foxes. But what benefit do island foxes provide bald eagles?  

Across the Channel Islands bald eagles are hatching out their 2018 chicks. Channel Island National Park reported that there are 13 active bald eagle nests across the islands this year and at least 22 known eggs.  

courtesy P. Sharpe

Three eaglets hatched in the Sauces Canyon nest last week on Santa Cruz Island. You can watch them 24 hrs a day via a webcam https://explore.org/livecams/bald-eagles/channel-islands-national-park-sauces-bald-eagle

Tonight, close observers saw some unexpected visitors to the bald eagle nest. Along with fish, the parent bald eagles have brought scavenged seal placenta back to the nest to feed their chicks. But with the darkness, something else stole up into the nest to eat the placenta bits. Circled in green, do you see the surprise scavengers? island deer mice.

captured image from the webcam 3/20/18

Who would have thought that hungry deer mice would come up into the bald eagle nest to eat meaty placenta. The eagle does not have night vision, it is a daytime hunter. It could hear the munching mice and would occasionally drive them off. Island deer mice are known to eat songbird eggs, and possibly chicks, when given the opportunity, (like when island fox populations were very low). The eaglets are small and without their parent's protection, would they be prey for the gang of deer mice? At one point six deer mice were visible.

Island foxes play an important role in controlling island deer mouse populations. 

Other bald eagle parents on the islands are sleeping soundly tonight, but the bald eagle with the messy nest is wide awake in the rain. It has two jobs tonight: keeping three eaglets warm and dry, and keeping the deer mice at bay. It will be a long night for this bald eagle, it needs an island fox.

Island foxes sometimes clean leftover food out of bald eagle nests. Island fox in a bald eagle nest.

New discovery of house mice attacking albatross chicks and nesting adults. 

Bald Eagle Recovery Spreads Across Channel Islands

Channel Islands National Park reported in July that 60 bald eagles are currently living across California's Channel Islands. In spring 2014 there were sixteen known breeding pairs and fourteen chicks successfully fledged or flew from the nest.

As bald eagles reestablish their population, they help protect island foxes by reducing the probability that golden eagles will colonize the islands. Bald eagles primarily prey on fish and seabirds, while the golden eagles prey specifically on mammals. In the late 1990s, golden eagles nearly caused the extinction of the island fox on three islands: San Miguel, Santa Rosa and Santa Cruz.

Milestone bald eagle birth in 2013.

A landmark this year was the return of bald eagles to San Clemente Island. It is believed this is the first time bald eagles have attempted to nest on this southern island in approximately 50 years. The U.S. Navy manages San Clemente Island and they have been successful in protecting island foxes and other island endemic species. The bald eagles are evidence of recovering habitat on the windswept island. 

The newly established pair was unsuccessful in nesting in 2014, but hopes are high that the pair will find success in the future.

According to the National Park Service the pair of bald eagles combine the successes found on the other Channel Islands. The female was hatched near Juneau, Alaska, in 2004. She was relocated as a juvenile to Santa Cruz Island as part of the efforts to reestablish bald eagles on the National Park islands.

The male eagle is a young adult, hatched in 2007. He began life in an incubator on Santa Catalina Island and was placed in a bald eagle nest on the island, where he was raised by foster eagle parents. 

With a number of active bald eagle nests on Santa Cruz and Santa Catalina Islands, the young pair looked south for territory of their own. Biologists hope that eventually all of the Channel Islands will have resident bald eagles. The recovery of the bald eagle and the island fox is dramatically interconnected. Success for the bald eagles supports island fox recovery and stability.


See Current Island Fox Recovery, island by island.

Bald Eagle Recovery on California Channel Islands

courtesy of Peter Sharp

The return of bald eagles to the California Channel Islands has been a slow but steady effort that has aided the Channel Island fox recovery on the northern islands. A robust bald eagle population keeps away golden eagles, island fox predators.  

Island fox recovery has been incredibly rapid. More typical of efforts to save endangered species, bald eagle conservation has spread across decades: 

• 1967 bald eagle listed as endangered species
• 1970s bald eagles become extinct on the Channel Islands
• 1980 - 1986: 33 young bald eagles are reintroduced to Catalina Islands 
• 1987: eggs laid by bald eagles on Catalina Island fail to survive because of continuing high levels of DDT in marine ecosystem
• 1989: bald eagle eggs taken from Catalina Island nests and incubated. Later hatchlings or foster chicks are returned to nests. 
• 2000 - 2002: juvenile bald eagles reintroduced to the northern Channel Islands 
• 2006 first chick hatched without human assistance on the Channel Islands in 50 years; female A-49
• 2007 bald eagle eggs hatch on Catalina Island without human assistance
• June 2007 bald eagle taken off of the Endangered Species List
• 2012 Female A-49 nests for the first time on Santa Cruz Island, but first chick does not survive
• 2013 MILESTONE EVENT - Female A-49 and mate become the parents of female chick A-89 the first second-generation bald eagle chick successfully fledged on the Channel Islands since the beginning of the recovery effort

According to the biologists managing the bald eagle recovery program, fifteen pairs of bald eagles attempted to nest on the Channel Islands last year. See a photo of A-89 and the full accounting of bald eagle nesting on the Channel Islands in 2013 at the Institute for Wildlife Studies.

As a large predatory bird, the bald eagle plays an important role on the California Channel Islands. For more about bald eagle recovery SEE Video: Return Flight: Restoring the Bald Eagle to the Channel Islands by the Filmmakers Collaborative