Black Skimmers at South San Diego Bay saltworks By J. KonecnyBlack Skimmers at South San Diego Bay saltworks By J. KonecnyBlack Skimmer (Rhynchops niger)
The Black Skimmer is unmistakable within its range. Its unusual voice, bill, and feeding behavior make it truly unique. The adult in breeding plumage is black above and white below with a white tail. The basal half of the laterally compressed bill is bright red with the distal half black. The lower mandible extends 2-3 cm beyond the upper, which is hinged and can be freely elevated and clamped shut. The wings are long and narrow.. The feet of Black Skimmers are bright red-orange and webbed. Their tail is short and is square or slightly forked
In the eastern U.S. skimmers are almost exclusively coastal; nesting on barrier beaches, shell banks, spoil islands, and salt marshes from Massachusetts and Long Island, NY, along the Atlantic and Gulf coasts to s. Mexico with isolated colonies on the . Yucatan Peninsula. In Florida, skimmers frequently occur inland, sometimes in large numbers, and have bred near Belle Grande in south.-central Florida and at Lake Okeechobee.
During the last three decades, Black Skimmers have become increasingly common along the southern California coast. The first Pacific coast record was in 1962 at the Santa Ana River mouth. Six years later they were observed at the Salton Sea and bred there in 1972. Until they began nesting at the San Diego saltworks in 1976, they were an irregular visitor to coastal southern California. Their breeding range expanded northward along the Pacific coast with breeding established at Bolsa Chica in 1985, Upper Newport Bay in 1986 and Terminal Island in 1998. They have continued to breed in most years at the Salton Sea and a small group (< 10 pairs) has bred irregularly in south San Francisco Bay since 1994. They have also bred in Batiquitos Lagoon since 1995. In addition to southern California the western population of Black Skimmers breeds south to Nayarit, Mexico.
Post-breeding Black Skimmers disperse from their breeding colonies but many over-winter in southern California. Winter roosts have typically been at Santa Barbara, Long Beach, Seal Beach and Mission Bay in San Diego. Typical winter roosting areas are located on public beaches, even those with a lot of human activity, or estuarine sand bars where they frequently associate with gulls and, occasionally, terns and shorebirds. Black Skimmers banded at Bolsa Chica and Upper Newport Bay have been noted at all of these wintering areas as well as in Ensenada and Bahia San Quintin in Baja California. A single individual was observed in winter far to the South near Mazatlan in coastal Mexico. Many color banded individuals from Salton Sea colonies have also been seen at the several coastal wintering sites.
Black Skimmers are highly nocturnal. Although they can occasionally be seen foraging in the daytime the bulk of their feeding activities and chick provisioning takes place from dusk to dawn. Skimmers forage mainly in tidal waters of bays, estuaries and lagoons but also utilize rivers, and salt marsh pools, creeks, and ditches; such habitats tend to concentrate small fish. They feed preferentially under low wind conditions when the water surface is smooth. They typically glide low over the water with their lower mandible slicing the surface of the water. When the mandible contacts a fish or other object, the maxilla clamps down while the head and neck tuck downward and back, securing the prey. Fish are then turned and swallowed headfirst or carried crosswise in the bill to the nest. There is much controversy over the foraging habitat of skimmers, with little information available on major food items; however, observed prey has been primarily small fish in range of 3-12 cm length (rarely up to 20 cm). The types of fish caught seem to depend on the region and local availability. At Bolsa Chica in 1995-1996 northern anchovy (23.6%) was the most commonly taken prey. Topsmelt (15.0%) California sardine (11.6%), California grunion (5.3%), California killifish (3.6%), mosquitofish (6.2%) and shadow gobies (8.6%) were also regular prey items. At the San Diego saltworks in 1995-1998 California sardine (20.9%) and topsmelt (16.8%) were the most abundant prey species with jacksmelt (3.0%), California grunion (6.8%), California halfbeak (8.6%), California killifish (6.8%), arrow goby (4.1%), Shadow goby (5.8%) and longjaw mudsuckers (3.9%) also recorded. The diversity of prey items taken is a reflection of the equally diverse foraging habits of Black Skimmers.
Most Black Skimmer breeding colonies are found on beaches, or sand islands, particularly in coastal southern California. In other parts of their range they utilize sand bars, dredge spoil islands, or salt marshes where they will nest of mats of dead vegetation. Proximity to Caspian Terns and other tern species is an important feature of skimmer colonies in southern California. During nest building, mates take turns scraping, using exaggerated sand-kicking posture (neck, head, bill, and tail elevated) with alternate foot strokes that throw sand backwards. Birds rotate in the scrape to create a saucer-shaped depression, similar to resting scrapes used throughout the year. The depression takes only a few minutes to create, but the process of nesting may involve several scrapes and nest showing behavior, requiring 5-7 days between onset of nest “building” and laying No material is added to the nest. Eggs are mainly ovate to elongated, crème-colored and blotched with varying amounts of black that blends well with the sandy environment. Egg laying begins 7 to 10 days the after first nest scrapes, appear. Eggs are laid in 1-2 day intervals with a typical clutch size of 3-4 eggs. Incubation period can be as short as 21-23 days but can last 23-25 days in areas of disturbance.
Post-breeding and wintering flocks in southern California regularly contain color-banded individuals from breeding colonies at the Salton Sea. Some of these have also been noted to remain and breed at Bolsa Chica, Upper Newport Bay and the San Diego Saltworks. There appears to be a lot of movement between wintering groups even within a single winter season. Black Skimmers seen in Santa Barbara have been seen within a few days in Long Beach and, later on, back in Santa Barbara. The same is true of birds in Mission Bay and Long Beach. In other cases marked individuals appear to remain at one wintering site all winter and also return to it in subsequent years. Some Black Skimmers show a degree of natal philopatry, returning to breed in their natal colonies; they breed for the firs time when two years old. Others have moved to different southern California colonies to breed and have been recorded at more than one colony in a single breeding season. One of the individuals which colonized San Francisco Bay had been banded earlier at Bolsa Chica.
Los Angeles Harbor is the northernmost nesting location for Black Skimmers in southern California. In 1998 and 1999, Skimmers nested on an area of newly deposited dredge fill. Black Skimmers initiated 10 nests in 1998 but none were successful. In 1999, they used another site adjacent to an area where Caspian Terns were also nesting. The skimmers initiated approximately 170 nests here in 1999, but productivity was poor, primarily due to high chick mortality and predation by gulls. In 2000, they again attempted nesting on the new fill area, this time within the 15-acre nesting site provided for Least Terns. They nested late in the Least Tern nesting season (late July), initiating approximately 115 nests but produced no fledglings, and most nests were abandoned by mid-August. There was no evidence of gull predation but high chick mortality and abandonment may have been due to frequent visits by Peregrine Falcons. Such late season nesting of Black Skimmers has frequently occurred at other nesting colonies, and may involve more pairs than earlier breeding attempts so not all can be attributed to re-nesting by birds which failed in an earlier nesting.
At Bolsa Chica, in 2003 and possibly in earlier years as well, late season predation of pre-fledging chicks by Peregrine Falcons may have caused nest abandonment and termination of breeding that season. They have been negatively impacted by nest predators (avian and terrestrial) at several of their breeding sites. When breeding in association with the larger and more aggressive Caspian Terns they may gain some protection from potential predators. However there is some disadvantage to nesting jointly with the large colonies of Elegant Terns. The large crèches of Elegant Tern chicks wander over their nesting colony and seem to disturb Black Skimmers tending eggs or small chicks. Trampling of smaller Black Skimmer chicks appears to have been an extra source of mortality. Black Skimmer reproduction was enhanced at Bolsa Chica in years when low fencing was used to keep the Elegant Tern chick crèches away from skimmer nests.
Their limited breeding range in southern California and most of their breeding being limited to only 3-4 colonies has resulted in the Black Skimmer being listed as a Bird Species of Special Concern in California.
By Dr. Charles Collins for FWS