Sleek, athletic, and equally adept at sea, on land, or in the sky, the cormorant is the triathlete of the bird world. These champion divers descend up to 150 feet beneath the water’s surface in search of fish and other aquatic prey. Sharp talons and powerful legs allow them to perch in trees as comfortably as they climb steep seaside cliffs or walk along the beach. With a wingspan that equals their body length (35 inches), these avian wonders soar, flying up to 200 miles in a single day. It’s no wonder cormorants are a winning design, with 42 living species spread around the world.
The white-breasted cormorant, the largest cormorant in its range, is native to South Africa and Namibia, like the African penguin. You might think two such superficially similar birds would compete for resources, but they fill different niches in the same habitat and ecosystem. Penguins are pelagic hunters—chasing prey out in the open ocean—while cormorants are coastal or demersal hunters, catching prey near the shore or bottom of a body of water. African penguins nest in burrows on the ground, while white-breasted cormorants nest in trees near water or on inaccessible rocks overlooking the sea. Like many seabirds, cormorants are colonial breeders. This means each nest is maintained independently by one socially monogamous pair, but all pairs nest in close proximity. There are downsides to having so many neighbors squabbles over space and resources are common—but together the colony deters predators that would make short work of a single pair.
Competition and Challenges
Even though cormorants are remarkable athletes and fill a role in their ecosystem, cultural attitudes toward them can vary significantly. In parts of China and Japan, cormorants were historically trained by fishermen—similar to how falconers use birds of prey—but in most of the world, they are often regarded as pests. Cormorants are culled by the thousands to protect commercial and sport fish populations, despite little evidence for the efficacy of this management strategy. Fish with economic value make up only a small percentage of the average cormorant’s diet. Undoing human damage to aquatic ecosystems is a more proven way to increase fish populations.
Cormorants also garner a negative reputation for their pungent guano (droppings). They favor nest sites overlooking the water, the same types of locations humans value for recreation and development. This leads to conflict in which cormorant nests are deliberately cut down or vandalized, leaving chicks to die. The same guano that makes such a stink has great benefits for the natural environment. It reduces seaside erosion, transfers nutrients from marine to terrestrial ecosystems, and fertilizes the phytoplankton and aquatic plants that make up the base of the food chain. And while their nesting habits and spatial needs can make their care complicated, the San Diego Zoo is home to a colony of white-breasted cormorants, which can be found in the African Marsh habitat below Eagle Trail.
White-breasted cormorant eggs are pale blue with a chalky calcium deposit when first laid. The blue fades over the course of incubation until the egg is white. This may allow females to detect and discard eggs laid later in her nest by another female.
Meet the Colony
Though cormorants at the Zoo may look identical, each individual has a unique personality. Three-year-old Brown, for example, is always eager to explore, while her older girlfriend seems most content as a homebody, sticking close to the nest. Pink collects sticks and feathers (long, pink flamingo feathers in particular), so she contributes most of the construction materials and nest defense in her relationship. Her mate, Yellow, spends more of his time carefully arranging the materials and sitting on eggs. The oldest male in the colony, Gold Daddy, earned his nickname for his gold color band and extreme enthusiasm for parenting. He allows his mate to do most of the incubation, but as soon as eggs hatch, he always takes over 90 percent of the chick rearing. Gold Daddy’s adult son, Red, models the same enthusiasm for feeding and brooding babies. Such attentive parenting pays off: this year, Gold Daddy became the colony’s first grandfather through Red’s production of offspring. And sometimes, perpetuating a species does take a village (or colony); while one of our cormorant pairs has never produced a fertile egg together, they have incubated and raised five foster eggs to adulthood.
Some cormorants mate for life, while others form temporary partnerships lasting a single season or a few years at a time. Regardless of how long they have been together, bonded cormorants constantly reaffirm their devotion to each other with entwined necks, stick-waggling, wing-waving, and gargling calls. Males and females are alike in appearance, and both initiate courtship, build the nest, and take care of chicks.
Because white-breasted cormorants are sensitive to nest disturbances and may abandon eggs or chicks—sometimes for a prolonged period—when stressed, wildlife care specialists at the Zoo have conditioned the colony to accept human proximity by offering high-value nest material by hand. Their favorite, sticks of freshly cut lavender, naturally repel mosquitos and other harmful insects. Now several of the cormorants will remain on the nest in exchange for a big bushel of lavender while specialists carefully reach under them to briefly exchange real eggs for dummy eggs. This allows us to candle eggs to check for fertility. Chick mortality is lower when they have fewer siblings to compete against, so if we candle a clutch and find that all the eggs in one nest are fertile, while a neighbor’s eggs are consistently nonviable, we can foster one or two of those fertile eggs under the infertile pair. When we are done candling, the cormorants get another big handful of lavender, and the specialist swaps the dummies back out for the real eggs.
The white-breasted cormorant is the largest of five cormorant species found in South Africa.
Careful Planning
The San Diego Zoo’s reproduction program has been quite successful. The colony has grown from 4 birds in 2016 to 35 individuals in 2024. Five adult cormorants from the San Diego Zoo Safari Park joined the Zoo colony in 2022, but the rest hatched on view to the public in the African Marsh habitat. Zoo visitors can watch the entire process, from nest building to hatching to young fledglings learning to swim, socialize, and navigate the wider habitat on their own. But of course, a lot of hard work and consideration went into creating this outcome.
The main factors contributing to a consistent increase in the Zoo’s white-breasted cormorant population are the changes in the way we manage birds. We no longer pinion cormorants, which has led to more successful nest building and foraging. We used insights from a trip to the Southern African Foundation for the Conservation of Coastal Birds (SANCCOB) to modify the way our colony’s nest structure was set up and how we presented nesting material to stimulate breeding behavior. We enclosed the habitat, which prevents wild herons and egrets from predating cormorant chicks. And we combined birds from two smaller colonies into one super colony.
Better Habits for the Future
Though the white-breasted cormorant population is relatively stable, there are several cormorant species at risk of extinction, including the bank cormorant and Cape cormorant of South Africa. Seabirds as a whole—a group that includes iconic birds like albatrosses, puffins, and penguins, in addition to less-revered birds like cormorants—have dropped 70 percent in number since 1950. Climate change, overfishing, ocean plastics, entanglement in fishing gear, oil spills, invasive species, disease, and human encroachment on coastal breeding habitat are all contributing to seabird decline. These are big, complex challenges that require global collaboration to resolve.
It may seem dire, but there are things you can do as an individual to help. You can avoid single-use plastics and dispose of trash properly, which decreases the amount of litter washing down storm drains and eventually out to sea. You can eat only sustainably harvested seafood. At the beach, be mindful not to disturb wildlife in their home. Local San Diego birds like the least tern, snowy plover, and Brandt’s cormorant nest on the coast and are adversely affected when people and pets cross barriers protecting breeding sites. Just learning about the great diversity of bird life in your own community and sharing that knowledge can encourage others to be mindful of how their actions impact birds, too.
Next time you are at the Zoo, or the beach, or a lake, stop and watch the cormorants for a moment. These underappreciated birds may surprise you!
