Why are Ospreys nesting on a crane?

Ospreys select a nest alongside water — rivers, lakes, coasts, or, in this case, San Francisco Bay. A high location is safe from predators on the ground and also provides the Ospreys a great view of the surrounding feeding areas and potential predators in the air. In rural areas, Ospreys usually choose to nest in trees, but in urbanized shorelines they often use human-made structures such as this historic crane.

Do Ospreys mate for life?

One Osprey male and one female typically build a nest and raise young; this kind of pair is called monogamous.  There are also records of one male with two females on nearby nests, which is called polygamous. Unless individual birds are banded by scientists, it’s difficult to tell if the birds on a nest are the same ones as last year.

How can you tell the male and female adult Ospreys apart?

Because of the web camera, we have close up views of the pair that has bonded and been defending the Whirley Crane’s nest.  The female is larger but whichever adult Osprey is nearer to the camera might look bigger.  They both have markings on their forehead.  The male’s forehead markings are sort of smudgy but the dark mark on the female’s forehead mark like one prominent polka dot or a raindrop shape.   The female has more dark speckly markings around the front of her chest, which is known as a female Osprey’s “necklace”.  We’ve named the female Rosie, which you can remember because she has one big polka dot on her forehead and a bunch of dots on her chest, reminiscent of the iconic Rosie the Riveter bandanas!   The male has been dubbed Richmond, in honor of the city to which he’s loyal.

Here’s a snapshot view that shows the differences.  Click the photo to enlarge

What is the Whirley Crane?

The Whirley Crane is an historic crane capable of rotating 360 degrees for rapid and highly maneuverable construction and loading of the Victory ships built during World War II in the historic Kaiser shipyards in Richmond, California. While it is no longer used, this Whirley Crane is the best remaining example of its kind, with a boom that is 110 feet long.  This Whirley Crane was operated by the famous “Rosie the Riveters”– women who worked in Richmond’s shipyards during the war to build ships for the American Pacific fleet.

Learn more by exploring the fascinating historic Richmond shoreline sites, including both the
SS Red Oak Victory ship (built by the Rosies) and the Whirley Crane right next to it in Shipyard 3.  We also encourage you to visit the Rosie the Riveter WWII Home Front National Historical Park.

How long have Ospreys been nesting on the Whirley Crane? How long have they been nesting in the Bay Area?

There are records of Ospreys nesting at the Whirley Crane site since 2012. Ospreys had long been documented nesting in certain parts of the Bay Area such as Kent Lake in Marin County, but it’s only since 2005 that significant numbers have been found nesting along the edge of San Francisco Bay.

How many Osprey nests are there in the Bay Area?

In 2016, there were 43 nests monitored by volunteers in the north or central part of San Francisco and San Pablo Bays.  More than 50 young Ospreys were fledged from among this population in 2016. Four years earlier in 2012, there were fewer than 20 nests.

When is Osprey nesting season? How long does it take for eggs to hatch?

Nesting season typically starts in March and goes through August.  Both parents incubate the eggs – about 36-42 days from when they are laid until they hatch. Osprey chicks spend a very long time in the nest after hatching. Sometimes they spend as many as 55 days before flying away from their nest.

How many eggs and chicks do Ospreys usually have?

A female Osprey typically lays three or sometimes four eggs. Not all the eggs hatch. The chicks that hatch later may not survive if the parents cannot find enough food to keep all their young well-fed.

How do the young Ospreys learn to fly? Are they in danger of falling out of the nest?

Young Ospreys practice moving in the nest, then spreading their wings and jumping into the air. They often prepare to fly by flapping their wings a lot, like exercise for their flight muscles. Young Ospreys have an instinctive impulse to fly but they learn by watching their parents.

There is a risk that young Ospreys may tumble or be knocked out of the nest before they can fly. However, there’s almost always at least one parent at the nest to protect the young before they’re ready to fledge.  Parents sometimes entice the fledglings to practice flying by offering a meal that the youngster has to fly to reach. 

Where do the adult and juvenile Ospreys go when nesting season is over?

We don’t know where our Bay Area adult and juvenile Ospreys go after August, but we’d love to learn more about their migratory routes and destinations! Many studies have been done on East Coast Osprey populations, but fewer have been conducted here on the Pacific flyway. Telemetry studies of East Coast breeding Ospreys have shown them traveling to Cuba or as far south as Brazil. A 1970s study of Ospreys from Idaho and Washington states showed that they travelled to Mexico and as far south as Ecuador in the winter.

How did you manage to install video cameras at the nest site?

We have two cameras in different spots on the Whirley Crane, each providing different views of the Ospreys and their surroundings. Installing these cameras required many layers of permissions and wonderful cooperation from many partners. We also hired HD camera experts with professional climbing skills, streaming media technologists, and technicians who worked on the crane and used specialized equipment to access portions of the crane. 

The cameras are remotely controlled so we will not disturb the Ospreys when adjusting the views. You may notice that you can see what the Ospreys are doing on their nest, even when it’s dark out.  That’s because we’re using the cameras in infrared mode to watch the Ospreys, but we are not using any visible light that would disturb the birds at this very sensitive time.


What can I do to help Bay Area Ospreys thrive?

There are a number of ways to help Ospreys. Restoring shoreline habitat creates a healthier Bay, with more fish for them to eat. Shoreline land managers can help by installing nest platforms that will provide safe nesting spots.  Recycling fishing line reduces the risk that Ospreys and other marine life will get entangled in improperly discarded line. We all can promote clean and healthy water in the Bay by avoiding the use of pesticides in our yards and by disposing of motor oil and toxic household chemicals at hazardous waste drop-off sites, not in gutters or storm drains.  You may also help us by becoming an osprey monitor.  Last but not least, you can support our efforts to protect Ospreys and other Bay Area birds by donating to Golden Gate Audubon or purchasing our souvenir Osprey merchandise.