By Paul Belz
May 5, 2016: The bird island tree at Lake Merritt, with Double-crested Cormorant nests on nearly all of its branches, makes a fine addition to Oakland's apartment buildings. These big, black relatives of pelicans fly from their nests to fish and return with meals for nestlings of all ages while onlookers train binoculars and cameras to get their Sunday morning thrill.
Three cormorant species make the Bay Area their home. Brandt's Cormorants (Phalacrocorax penicillatus) and Pelagic Cormorants (Phalacrocorax pelagicus) favor coastlines and offshore islands, while Double-crested Cormorants (Phalacrocorax auritus) venture from the coast to estuaries and freshwater.
Kristin Butler from the San Francisco Bay Bird Observatory (SFBBO) described how they have collected data on colonial water birds at Lake Merritt for 30 years. 'Colonial water birds' refers to species like gulls, terns, egrets, herons, and cormorants; shore, estuary, and freshwater birds that nest in large groups. This colonial nesting strategy increases nestlings' chances of avoiding predators. The SFBBO, a research-oriented organization, shares its findings with the Audubon Society and other advocacy groups.
Kristin commented that Lake Merritt's cormorants live and seek food by themselves before and after nesting season. Because of difficulties with funding for certain types of research, no one bands individual birds to keep track of their movements. As a result, ornithologists do not know where they go after nesting season, or if the same birds return to nest here every year.
Kristin introduced Jean Halford, a volunteer who has studied birds in many countries and who currently monitors the Lake Merritt cormorants. Jean noted that Snowy Egrets and Black-crowned Night Herons nested on this island until the cormorants' population expanded here in 2006. No one knows exactly why the herons and egrets moved away, but the egrets and herons now nest in trees near the main post office in downtown Oakland, near 14th and Harrison Streets. Jean had counted three to five active nests on the island's little trees in February 2016, 40 in April, and 90 in early June. She speculated this number marked the season's peak.
Male Double-crested Cormorants cry“Aawwk!” hoarsely and show the electric blue colors of their beaks' interiors to attract females and to discourage rivals from approaching their nesting spots. Other than these displays, they claim branches on a first come first served basis, and don't tend to fight each other.
The parents, who remain monogamous for the nesting season, work together to build the nests. The female lays three to seven eggs, which both parents incubate for 25 to 29 days. It can take between two days to a week for all the eggs to hatch. The nest can be crowded, and older chicks sometimes push their younger siblings out.
Newly independent fledglings stay together in groups while parents watch them from branches. The young will soon begin their independent adult lives, and maybe some will return to nest here!
The birders watched as cormorant parents flew from the water to the nesting tree. Down- covered heads suddenly appeared above nests' rims, and the young waved their necks to beg for food. Kristin and Jean shared binoculars, and invited everyone to volunteer with SFBBO to help watch over these beautiful and mysterious birds.
By Paul Belz