Mysterious Declines: The American Kestrel

Cover photo: © Gregory “Slobirdr” Smith, 2007, some rights reserved.

Learn about North America’s smallest falcon and its mysterious decline across the United States.

Cover photo: © Gregory “Slobirdr” Smith, 2007, Flickr Photo Album, some rights reserved.

Places to See American Kestrels

Pearson-Arastradero Circle

Pearson-Arastradero Preserve

American kestrels are experiencing declines throughout the United States, including coastal California.

Data from the Peregrine Fund’s American Kestrel Partnership suggest that the coastal California population has been experiencing declines since the 1960’s.

Scientists do not know the “one true cause” of kestrel declines in the United States; rather, they believe that multiple causes could be working together to depress populations. Possible causes include habitat loss, the use of neonicotinoid insecticides, and local threats from the use of anticoagulant rat poisons.

Many local organizations are working to construct artificial kestrel nesting boxes to help the numbers in their area. For more information on how to construct a kestrel nesting box, check out this page by the Cornell Lab of Ornithology’s NestWatch.

American kestrels are North America’s smallest falcon.

They are about the size of a mourning dove, measuring in at 8.7 – 12.2 inches in length. Male American kestrels have beautiful slate-blue wings and rusty backs/tails. Females, on the other hand, are more subtly-beautiful – they have rusty wings and backs. Both males and females have black “slashes” on their faces.

You can often recognize American kestrels by looking for a bobbing head or tail. This charming behavior makes these birds distinctive on telephone wires, even at a distance.

American Kestrel 3
Male American kestrel; Source: © Matthew Buynoski, 2018, all rights reserved.

American kestrels eat large insects, small reptiles and amphibians, and even the occasional small bird.

American kestrels are raptors, meaning that they subdue and kill their prey using their feet. They hunt by swooping down on small prey and grabbing it in their talons.

Kestrels will sometimes cache, or store, extra food to keep it for later consumption or hide it from other animals.

American kestrels are secondary cavity-nesters, meaning that they build their nests in cavities excavated by other animals.

Once established at their nest site, female kestrels lay 4 – 6 eggs that are incubated by both parents. After about a month, the eggs hatch. The young and the female are fed by the male for a couple of weeks, after which the female leaves and begins to forage as well. The young begin to fly about a month after hatching.

American kestrel at Pearson-Arastradero Preserve; Source: © Matthew Buynoski, 2018, all rights reserved.

Cool facts about American kestrels:

  • American kestrels are also known as “sparrow hawks” or “mousers”.
  • Only the northern populations of American kestrels migrate south during the winter. Central and southern populations are permanent residents.
  • American kestrels have a very distinct and excitable call, making these birds easy to locate by sound. To hear the American kestrel call, check out this page.

Resources to learn more:

American Kestrel 2
Male American kestrel in flight; Source: © Matthew Buynoski, 2018, all rights reserved.

Explore Salt Ponds and Marsh at Alviso Marina County Park

Alviso, Ca – Connect with a site that’s a part of one of the largest tidal marsh restoration projects on the west coast. Alviso Marina County Park was formerly an industry-dominated site, but now serves as an amazing entrance to the greater Don Edwards San Francisco Bay National Wildlife Refuge.

About the Park

Alviso, Ca – Santa Clara County Park 

Science Spotlight: Leopard Sharks at Alviso

When I first learned that there were actual sharks around Alviso, I was in total shock. To me, the idea of the perfect habitat for sharks had always been the open ocean. Thus, you can imagine my surprise when I learned that the area is home to leopard sharks.

Leopard sharks are the most common sharks in the San Francisco Bay estuary, with a range that extends from Oregon to Mexico. They can grow to lengths of up to 7 feet, and feed on invertebrates and fish. To feed, they make a daily migration to shallow areas during high tides.

The San Francisco Bay Area lost much of the tidal marsh and shallow areas utilized by the leopard sharks to development for harvesting salt. As these tidal marshes are restored, researchers are finding that the leopard sharks are returning.

Leopard shark; Source: © Nathan Rupert, 2009, Flickr Photo Album, some rights reserved.

Park History

Visiting Alviso truly feels like a blast into the past: on your way to the park, you pass by an old cannery site, the warehouses, and a Victorian-style home. The area that is now Alviso Marina County Park used to be receive drainage rich in mercury from the New Almaden Mining District. The site also used to be a heavily-trafficked port area supplying San Jose and a launching point for steamboat passage to San Francisco. When these operations shut down, the area was transformed into salt ponds for salt harvest, operated by the Cargill Salt Company.

The area is now rich with wildlife, providing a feeding and nesting area for many species of birds. Alviso Marina County Park has become a part of the nearby Don Edwards San Francisco Bay National Wildlife Refuge. Today, the area is part of the South Bay Salt Pond Restoration Project (SBSPRP), one of the largest tidal marsh restoration projects on the west coast. Restoration offers new habitat for California wildlife and offers visitors the chance to see nature reclaiming a formerly industry-dominated area.

For more detailed information on the history of Alviso Marina County Park, check out this article by the Mercury News.

Visit the Park

Please note that there is no entrance fee to enter the park. Dogs are now allowed on trails or walkways. For more detailed information on where dogs are and aren’t allowed, check out the park map.

Alviso Marina County Park serves as the entrance to the greater Don Edwards San Francisco Bay National Wildlife Refuge. We encourage you to explore that area as well, time permitting.

Here are some helpful resources to plan your visit:



Hike Along Streams at Redwood Regional Park

Oakland, Ca – Just outside of the East Bay’s urban sprawl, Redwood Regional offers visitors the chance to see second and third-generation redwoods and a recovering stream habitat.

Species to Look Out For

About the Park

Oakland, Ca – Regional Park

Science Spotlight: Rainbow Trout at Redwood Regional

The rainbow trout is a native Californian fish species, originally found on the western coast of North America. They require good quality water to survive and reproduce. so they have become symbols of healthy American watersheds.

Their introduction to freshwater streams worldwide has resulted in their spread from their historical range. Rainbow trout have now spread to all continents in the world except for Antarctica. However, don’t be fooled by the expanded range – the rainbow trout is facing declines due to loss of quality habitats, pollution, and water diversion (to name a few). As a result, multiple species of steelhead (a special form of rainbow trout whose strategy is to migrate to the ocean as juveniles) are federally listed as endangered or threatened.

The rainbow trout’s freshwater stream habitat at Redwood Regional Park is threatened by erosion. The erosion, caused by heavy traffic from hikers, dogs, and bicyclists, causes accumulation of sediments and a decrease in stream water quality. These effects impact multiple species that use the stream for breeding – including rainbow trout and the “Special Concern”-listed California newt.

To do your part in restoring freshwater streams, be sure to stay on the trails and refrain from allowing pets to enter the stream.

Park History

Redwood Regional Park shares its legacy with many other Bay Area parks as a redwood forest ravaged by logging. The redwoods that remain today are second and third-generation kin to the giants that once stood at the park.

Visit the Park

Please note that there is a $5 vehicle fee to enter the park. Dogs are allowed on leashes, but an additional fee of $2 is charged per dog.

Here are some helpful resources to plan your visit:


Visit California’s First State Park: Big Basin State Park

Boulder Creek, Ca – In 1902, Big Basin became California’s first state park. Today, it protects one of the largest continuous stretches of old-growth coast redwood south of San Francisco.

Species to Look Out For

About the Park

Boulder Creek, Ca – State Park

Science Spotlight: Keeping it “Crumb Clean” in California’s Parks

Marbled murrelets are small, robin-sized seabirds that have one very interesting quality: they build their nests high up in redwood trees. Redwood forest habitats have suffered from logging during the gold rush, which in turn has contributed to the steep declines of marbled murrelet populations.

Steller’s Jays and other avian predators have been shown to negatively impact marbled murrelet populations by eating their eggs and young, according to a study at Redwood National and State Parks.

Steller’s jays are crested blue and black birds commonly found at campgrounds, attracted there by food leftover from humans. The high jay density is thought to increase  the chances of Steller’s jays finding and predating the nests of marbled murrelets.

Image result for crumb-free sign marbled murrelet stellers jay sign
A common sign at campgrounds, featuring a Steller’s jay and a warning to clean up all traces of food. Source: Save the Redwoods League.

Public education programs, such as the “Crumb Clean” initiative depicted above, warn people that food waste has the potential to impact marbled murrelet populations by attracting their predators.

The moral of the story? Be careful of leaving any trace on your hikes – even a crumb can make a difference!

For more information on marbled murrelets and Steller’s jays, check out the Bay Area Naturalist article “Logging, Crumbs, and Lost Fish: The Story of the Marbled Murrelet“.

Park History

In 1902, Big Basin State Park became the first state park established in California. Its land protects mostly redwood forest and is home to the largest continuous stretch of old-growth redwoods south of San Francisco. Scientists estimate that the older trees in the park range from 1,000 to 2,500 years old.

Prior to the arrival of Europeans, Native Americans inhabited the park’s land for thousands of years. Evidence of the Native American’s land use can be seen in the bowl-like depressions in rocks along the trail. These depressions were used by the Ohlone people to grind seeds and acorns into flour.

In the midst of logging in the late 1800’s, a small group of citizens formed the Sempervirens Club (sempervirens being the species name of coast redwoods). They spurred a movement amongst California’s citizens, which resulted in the creation of a bill to protect the park area. The park is currently over 18,000 acres and growing.

Visit the Park

Please note that there is a $10 vehicle fee at the park. Dogs are not allowed on trails, but are allowed on leashes at picnic areas.

Here are some helpful resources to plan your visit:


Colorful Corvid: The Yellow-billed Magpie

Cover photo: © Marcel Holyoak, 2011, some rights reserved.

Did you know that our site logo is a yellow-billed magpie? Learn more about why we chose this stunning bird.

Cover photo: © Marcel Holyoak, 2011, Flickr Photo Album, some rights reserved.

Yellow-billed magpies are the inspiration for Bay Area Naturalist’s logo as bright, personable birds that are only found along California’s coasts and Central Valley. While their restricted range makes them very special to see, it also makes them susceptible to the threats that climate change poses to our planet’s life. They inhabit open oak woodlands – a specialized habitat that could mean that this species will not be able to adapt well to changes brought about by our changing climate.

For more information on why we chose the yellow-billed magpie as our logo, check out our Site Logo page.

Yellow-billed magpies are found in California’s Central Valley and along the coast.

This species is endemic to California, meaning that they are only found in our state. Its range is quite restricted, covering an area just 500 miles long and 150 miles wide. They are found in open oak woodland habitats, usually near bodies of water.

Although they’re not found in the heart of the Bay Area, they can be seen in parts of the East and South Bay. Coyote Valley Open Space Preserve and Joseph D. Grant County Park are excellent places to see yellow-billed magpies in the Bay Area.

Yellow-billed magpies have a diverse diet.

They eat insects, fruits, seeds, and will scavenge for food. They have also been known to be kleptoparasitic, or steal food from other animals.

Yellow-billed magpies construct large, dome-shaped nests.

Often found on oak limbs, their nests are lined with mud on the inside. They nest in colonies of 3 to 30 pairs that maintain loose association with one another. They lay 5-8 eggs on average.

The female incubates the eggs, sustained by food brought from the male. After 18 days of incubation, the young hatch. Both of the parents will participate in feeding and caring for the offspring.

Yellow-billed magpie nest; Source: DavisWiki

Yellow-billed magpies were hit hard by West Nile Virus.

In 2004 when West Nile Virus established itself in California, yellow-billed magpie populations suffered. It is estimated that the virus killed half of their population in just two years. Habitat loss and pesticide-use also threaten this species.

Cool facts about yellow-billed magpies:

  • The oldest yellow-billed magpie ever found was just shy of 10 years old.

Resources to learn more:

Enjoy a Hike with Your Pooch at Ed R. Levin County Park

Milpitas, Ca – If you’ve got a furry companion, this is the place to be! Ed R. Levin County Park allows dogs on-leash and has an off-leash dog park right near the trail entrance. Perfect for a weekend out with Clifford.

About the Park

Milpitas, Ca – Santa Clara County Park

Visit the Park

If you’ve been hiking around the Bay Area, you know that it’s usually a toss-up as to whether or not dogs are allowed at the park. Ed R. Levin County Park is special, as it allows dogs and has an off-leash dog park.

Please note that there is a $6 vehicle fee to enter the park. Dogs are allowed on leashes.

Here are some helpful resources to help plan your visit:

Dogs & Parks – Why Restrict Dog Access?

Dogs, especially when off-leash at parks, are in an area with many other wild animals. In some cases, this can lead to unexpected altercations between dogs and wildlife. Thus, keeping dogs off trails is a way to protect them from harmful interactions such as these.

Beyond that, dogs can also pose a threat to wildlife at the park you’re exploring. Many dogs are curious, and will excitedly greet any new acquaintances made on the trail. However, some species, such as the Western snowy plover, are extremely stressed by events such as these. Snowy plovers are already facing steep population declines from habitat loss and disturbance, so protecting their populations from any sort of stress is critical.