The Coyotes Arrived. Now, They’re Changing Angel Island.
Just over a mile of water lies between Angel Island and the mainland town of Tiburon. During high winds and currents, kayakers tend to steer clear of this channel known as Raccoon Strait, which carries some of San Francisco Bay’s strongest and deepest waters. Nonetheless, some swimmers choose to fight the tides, including Olympians competing in the Tiburon Nautical Mile Swim, and a few furry, four-legged canines with a steadfast determination to reach an island buffet. For as long as California State Parks (CSP) staff can remember, they have never encountered coyotes on Angel Island. Then in 2017, a disbelieving ranger spotted a coyote, and then another one and another one. As the new top predator spreads across the 1.2 square mile island, the cascade of their effects on the local ecology is turning researchers’ heads. Scientists from the California Department of Fish and Wildlife (CDFW) collected data on the island this October, hoping to learn about the coyotes’ watery crossings and impact on the island deer population. “We do know coyotes have been expanding south into Marin County and to San Francisco. They’re already taking exploratory things like going across the Golden Gate Bridge,” says Brett Furnas, a CDFW quantitative ecologist. “So it’s not a stretch that they would, maybe by accident, get swept across to Angel Island, or intentionally do that.” Coyote swimming towards Tiburon from Angel Island this April, its head just barely visible (Left, Photo by Casey Dexter-Lee); Coyote getting its legs wet on the shores of Angel Island looking towards Tiburon (Right, Photo by California State Parks/Bill Miller) The idea of coyotes on Angel Island has been floated before. In 1915, the US Army introduced about 20 Columbian black-tailed deer (Odocoileus hemionus) to Angel Island for hunting, but stopped in the 1950s when the island became a state park. Over the next 50 years, the deer population exploded to as high as 300. It was the state’s highest documented density of deer—a record likely still standing in California. “The deer were starving and skinny, and there was a concern for the impacts on the island’s cultural plants and vegetation,” says Bill Miller, a CSP environmental scientist. Native plants on the island that deer are known to feed on include sagebrush, chamise, and purple needlegrass. “There were all sorts of suggestions thrown out,” says Miller. “We could relocate some. We could introduce coyotes onto the island. We could maybe introduce contraceptives.” Angel Island fawns lounging in 2010 (Matt Baume via Flickr, CC by-SA 2.0); An Angel Island doe dashing across the street (Torroid via Flickr, CC BY-SA 2.0) Relocating coyotes to Angel Island was proposed in 1981 by Dale McCullough, a wildlife biologist and former professor at UC Berkeley. He advocated for bringing over a small pack of six coyotes to prey on the sick deer and fawns damaging the island’s trees and shrubs. Native to California and most of the US, coyotes (Canis latrans) can survive almost everywhere, from dry deserts to foggy coasts. In the past fifty years, their numbers and range have expanded into sprawling cities and suburbs, where they feed on cats, small dogs, rats, trash, and fruit. McCullough’s coyote proposal, however, fell flat. Originally in favor of the plan, the California Department of Fish and Game succumbed to the backlash from the public and animal rights groups, and withdrew the proposal to naturally control the deer population with predators. “In the end, state parks went with a culling program, and over the years, it would cull deer every few years,” says Miller. “But then at some point, the culling stopped and the numbers of deer on the island apparently stabilized… Shortly after, the coyotes showed up.” Coyote perched on a rocky outcrop, and a nonchalant pair on the street looping around Angel Island (California State Parks/Michael Dolan) Parks employee Mikayla Smith first saw a coyote on the lawn of the Parks staff residences in 2017. But she was met with disbelief when Parks staff told her coyotes didn’t exist on the island. Her sighting was dismissed until another Parks employee, Andrew Luskus, caught a glimpse of one. When Luskus turned the corner on his bike along the four-mile fire trail that circles the island, he made split-second eye contact with a coyote, before it scampered into the bushes. “Are you sure it wasn’t a dog?” fellow Parks employees asked. He had seen many coyotes during his time as a Parks ranger in Death Valley—he was sure. Within a year after Luskus’ sighting, Parks staff began hearing them. Ferry workers were seeing them. “I’ve seen coyotes swim across Raccoon Strait,” wrote Ashley Kristensen, the operations manager who has worked at the Angel Island-Tiburon Ferry for 15 years. Aaron Swerkes, a fifth-year ferry captain who has sailed in the Bay for the past thirty years, has seen coyotes in the strait just a couple times since his first sighting about a decade ago. The first litter of pups appeared in 2019. And with it, a trophic cascade—a domino effect that begins when top predators impact the behavior or abundance of their prey, trickling down to the rest of the food chain. Coyote pups in a redwood grove near the southern tip of the island on June 21, 2024 (Omar Babovic)Perhaps the most famous example of a trophic cascade is the reintroduction of gray wolves to Yellowstone National Park, after they were shot, trapped, and poisoned into extinction in the 1930s. Without their top predator, elk were unafraid in the open and as a result overgrazed on young brush and trees, leaving scientists concerned about erosion and plant die-off. From 1995 to 1996, the National Parks Service released thirty-one gray wolves to prey on the elk. In just five years, willow and aspen stands recovered along riverbanks. Beavers and other wildlife began to thrive, and even the course of the river itself changed as a result. At Angel Island, a similar cascade has begun. Now a menu item, deer timidly skirt among shrubs and bushes. “Around the time the last ferry left, the deer would come and hang out on the lawn in the visitors center,” says Casey Dexter-Lee, the State Parks Interpreter II who has lived on the island for 14 years. “Now, they aren’t in this open space as much and are a bit more cautious.” While bucks remain gallivanting the streets, armed with their antlers, fawn and doe are rarer sights. Since the litter’s arrival, Parks staff have not witnessed any deer grow into adulthood, according to Dexter-Lee, though it is possible that they were raised on remote, hidden parts of the island. “I do know that coyotes are eating deer and fawn,” says Miller. “Staff have told me that, and when we were out there last week, I found a deer hoof in coyote scat.” Angel Island Parks Interpreter II Casey Dexter-Lee looking at some coyote scat on the road, and also, a buck (Jillian Magtoto) Raccoons, too, are no longer a common sight. They used to steal and beg from people, who were concerned about seeing them in the daytime, since it is usually a sign of sickness or rabies, says Dexter-Lee, Now, they’re no longer a problem. Dexter-Lee also wouldn’t mind if the coyotes kept the Norwegian rats under control, which arrived on 19th and 20th-century ships, and have since disrupted the growth of native plants and the wildlife that relies on them. Still, scientists and staff worry that one endemic species could suffer from predation: the Angel Island mole. It’s slightly larger than other East Bay moles with a broader nose, bigger feet, heavier front claws, and slightly darker coloring. “The Angel Island mole is a subspecies of mole that is only found on this island,” says Miller. “But I don’t know what their numbers are or if coyotes are eating them or not.” Raccoon in the brush of Angel Island in 2018 (l Rocky Ordoñez via iNaturalist, CC0); The pictured broad-footed mole (Scapanus latimanus) is found primarily in California and Baja California with at least 12 subspecies, including S.I. insularis on Angel Island. (Bob Dodge via iNaturalist, CC-BY-NC 4.0) As for change in island plant life, so far there isn’t any, says Dexter-Lee. But we can make some predictions. “With less grazing pressure we may see more diversity, an increase in non-resistant browse, and a denser forest with smaller and more abundant stems,” says Miller. For Angel Island, he adds, less deer may mean more oak trees. In a seemingly endless cornucopia of food options, the coyotes appear to live in an island paradise. They regularly munch the fallen fruit beneath the Catalina cherry and Canary Island date palm trees, enriching their varied omnivorous diet. Unrestricted by their crepuscular clock, they encounter visitors and staff at all hours of the day. Trails and roads are overrun by their scat. They loiter among picnic tables where visitors might leave behind crumbs. Since the first litter in 2019, Parks staff have observed small coyotes and pups every year. But the extent of their growth has limits. “There’s only so much food and space to support coyotes on an island,” says Furnas, who leads the CDFW’s investigation of coyote and deer populations on Angel Island. A coyote pounces and triumphantly snacks on an underground critter near the docks and Visitor’s Center picnic tables on Angel Island (Video by Jillian Magtoto)Since September, the CDFW has been collecting coyote scat and installing wildlife cameras to determine their genetics, diets, and movements. The island’s isolation presents a unique opportunity to learn how coyotes control deer populations in a closed environment, says Furnas. He suspects the coyotes are doing so by feeding on fawns, whose first year of survival is often the most critical limitation for population growth. Whether the coyotes seek food and partners beyond the island, however, remains unknown. “As long as there is enough food for them, do they stay on Angel Island, or do they go back to the mainland?” Furnas asks. “On islands, you can have genetic inbreeding… So for a healthy population, you’re going to want to have genetic mixing as well.” The CDFW hopes to provide deer and coyote population estimates within a year. Whether it plans to answer other questions of reproduction rates, genetic diversity, and interspecies dynamics depends on if the study continues in the future. But for now, if you find yourself gazing across Raccoon Strait from the island, mainland, or ferry, keep your eyes peeled for a coyote’s head bobbing in the water.
Deer and raccoons that once fearlessly roamed the island, have become prey. The post The Coyotes Arrived. Now, They’re Changing Angel Island. appeared first on Bay Nature.
Just over a mile of water lies between Angel Island and the mainland town of Tiburon. During high winds and currents, kayakers tend to steer clear of this channel known as Raccoon Strait, which carries some of San Francisco Bay’s strongest and deepest waters. Nonetheless, some swimmers choose to fight the tides, including Olympians competing in the Tiburon Nautical Mile Swim, and a few furry, four-legged canines with a steadfast determination to reach an island buffet.
For as long as California State Parks (CSP) staff can remember, they have never encountered coyotes on Angel Island. Then in 2017, a disbelieving ranger spotted a coyote, and then another one and another one. As the new top predator spreads across the 1.2 square mile island, the cascade of their effects on the local ecology is turning researchers’ heads. Scientists from the California Department of Fish and Wildlife (CDFW) collected data on the island this October, hoping to learn about the coyotes’ watery crossings and impact on the island deer population.
“We do know coyotes have been expanding south into Marin County and to San Francisco. They’re already taking exploratory things like going across the Golden Gate Bridge,” says Brett Furnas, a CDFW quantitative ecologist. “So it’s not a stretch that they would, maybe by accident, get swept across to Angel Island, or intentionally do that.”
Coyote swimming towards Tiburon from Angel Island this April, its head just barely visible (Left, Photo by Casey Dexter-Lee); Coyote getting its legs wet on the shores of Angel Island looking towards Tiburon (Right, Photo by California State Parks/Bill Miller)
The idea of coyotes on Angel Island has been floated before.
In 1915, the US Army introduced about 20 Columbian black-tailed deer (Odocoileus hemionus) to Angel Island for hunting, but stopped in the 1950s when the island became a state park. Over the next 50 years, the deer population exploded to as high as 300. It was the state’s highest documented density of deer—a record likely still standing in California.
“The deer were starving and skinny, and there was a concern for the impacts on the island’s cultural plants and vegetation,” says Bill Miller, a CSP environmental scientist. Native plants on the island that deer are known to feed on include sagebrush, chamise, and purple needlegrass. “There were all sorts of suggestions thrown out,” says Miller. “We could relocate some. We could introduce coyotes onto the island. We could maybe introduce contraceptives.”
Angel Island fawns lounging in 2010 (Matt Baume via Flickr, CC by-SA 2.0); An Angel Island doe dashing across the street (Torroid via Flickr, CC BY-SA 2.0)
Relocating coyotes to Angel Island was proposed in 1981 by Dale McCullough, a wildlife biologist and former professor at UC Berkeley. He advocated for bringing over a small pack of six coyotes to prey on the sick deer and fawns damaging the island’s trees and shrubs.
Native to California and most of the US, coyotes (Canis latrans) can survive almost everywhere, from dry deserts to foggy coasts. In the past fifty years, their numbers and range have expanded into sprawling cities and suburbs, where they feed on cats, small dogs, rats, trash, and fruit.
McCullough’s coyote proposal, however, fell flat. Originally in favor of the plan, the California Department of Fish and Game succumbed to the backlash from the public and animal rights groups, and withdrew the proposal to naturally control the deer population with predators.
“In the end, state parks went with a culling program, and over the years, it would cull deer every few years,” says Miller. “But then at some point, the culling stopped and the numbers of deer on the island apparently stabilized… Shortly after, the coyotes showed up.”
Coyote perched on a rocky outcrop, and a nonchalant pair on the street looping around Angel Island (California State Parks/Michael Dolan)
Parks employee Mikayla Smith first saw a coyote on the lawn of the Parks staff residences in 2017. But she was met with disbelief when Parks staff told her coyotes didn’t exist on the island. Her sighting was dismissed until another Parks employee, Andrew Luskus, caught a glimpse of one. When Luskus turned the corner on his bike along the four-mile fire trail that circles the island, he made split-second eye contact with a coyote, before it scampered into the bushes. “Are you sure it wasn’t a dog?” fellow Parks employees asked. He had seen many coyotes during his time as a Parks ranger in Death Valley—he was sure.
Within a year after Luskus’ sighting, Parks staff began hearing them. Ferry workers were seeing them. “I’ve seen coyotes swim across Raccoon Strait,” wrote Ashley Kristensen, the operations manager who has worked at the Angel Island-Tiburon Ferry for 15 years. Aaron Swerkes, a fifth-year ferry captain who has sailed in the Bay for the past thirty years, has seen coyotes in the strait just a couple times since his first sighting about a decade ago.
The first litter of pups appeared in 2019. And with it, a trophic cascade—a domino effect that begins when top predators impact the behavior or abundance of their prey, trickling down to the rest of the food chain.
Perhaps the most famous example of a trophic cascade is the reintroduction of gray wolves to Yellowstone National Park, after they were shot, trapped, and poisoned into extinction in the 1930s. Without their top predator, elk were unafraid in the open and as a result overgrazed on young brush and trees, leaving scientists concerned about erosion and plant die-off. From 1995 to 1996, the National Parks Service released thirty-one gray wolves to prey on the elk. In just five years, willow and aspen stands recovered along riverbanks. Beavers and other wildlife began to thrive, and even the course of the river itself changed as a result.
At Angel Island, a similar cascade has begun. Now a menu item, deer timidly skirt among shrubs and bushes. “Around the time the last ferry left, the deer would come and hang out on the lawn in the visitors center,” says Casey Dexter-Lee, the State Parks Interpreter II who has lived on the island for 14 years. “Now, they aren’t in this open space as much and are a bit more cautious.” While bucks remain gallivanting the streets, armed with their antlers, fawn and doe are rarer sights. Since the litter’s arrival, Parks staff have not witnessed any deer grow into adulthood, according to Dexter-Lee, though it is possible that they were raised on remote, hidden parts of the island. “I do know that coyotes are eating deer and fawn,” says Miller. “Staff have told me that, and when we were out there last week, I found a deer hoof in coyote scat.”
Angel Island Parks Interpreter II Casey Dexter-Lee looking at some coyote scat on the road, and also, a buck (Jillian Magtoto)
Raccoons, too, are no longer a common sight. They used to steal and beg from people, who were concerned about seeing them in the daytime, since it is usually a sign of sickness or rabies, says Dexter-Lee, Now, they’re no longer a problem. Dexter-Lee also wouldn’t mind if the coyotes kept the Norwegian rats under control, which arrived on 19th and 20th-century ships, and have since disrupted the growth of native plants and the wildlife that relies on them.
Still, scientists and staff worry that one endemic species could suffer from predation: the Angel Island mole. It’s slightly larger than other East Bay moles with a broader nose, bigger feet, heavier front claws, and slightly darker coloring. “The Angel Island mole is a subspecies of mole that is only found on this island,” says Miller. “But I don’t know what their numbers are or if coyotes are eating them or not.”
Raccoon in the brush of Angel Island in 2018 (l Rocky Ordoñez via iNaturalist, CC0); The pictured broad-footed mole (Scapanus latimanus) is found primarily in California and Baja California with at least 12 subspecies, including S.I. insularis on Angel Island. (Bob Dodge via iNaturalist, CC-BY-NC 4.0)
As for change in island plant life, so far there isn’t any, says Dexter-Lee. But we can make some predictions.
“With less grazing pressure we may see more diversity, an increase in non-resistant browse, and a denser forest with smaller and more abundant stems,” says Miller. For Angel Island, he adds, less deer may mean more oak trees.
In a seemingly endless cornucopia of food options, the coyotes appear to live in an island paradise. They regularly munch the fallen fruit beneath the Catalina cherry and Canary Island date palm trees, enriching their varied omnivorous diet. Unrestricted by their crepuscular clock, they encounter visitors and staff at all hours of the day. Trails and roads are overrun by their scat. They loiter among picnic tables where visitors might leave behind crumbs. Since the first litter in 2019, Parks staff have observed small coyotes and pups every year.
But the extent of their growth has limits. “There’s only so much food and space to support coyotes on an island,” says Furnas, who leads the CDFW’s investigation of coyote and deer populations on Angel Island.
Since September, the CDFW has been collecting coyote scat and installing wildlife cameras to determine their genetics, diets, and movements. The island’s isolation presents a unique opportunity to learn how coyotes control deer populations in a closed environment, says Furnas.
He suspects the coyotes are doing so by feeding on fawns, whose first year of survival is often the most critical limitation for population growth. Whether the coyotes seek food and partners beyond the island, however, remains unknown.
“As long as there is enough food for them, do they stay on Angel Island, or do they go back to the mainland?” Furnas asks. “On islands, you can have genetic inbreeding… So for a healthy population, you’re going to want to have genetic mixing as well.”
The CDFW hopes to provide deer and coyote population estimates within a year. Whether it plans to answer other questions of reproduction rates, genetic diversity, and interspecies dynamics depends on if the study continues in the future. But for now, if you find yourself gazing across Raccoon Strait from the island, mainland, or ferry, keep your eyes peeled for a coyote’s head bobbing in the water.