Black skimmers are unique, magnificent birds

By Robin Bjork
Dec. 21, 2017 at 9:54 p.m.
Updated Dec. 22, 2017 at 6 a.m.

The black skimmer are the only known birds with vertically shaped pupils.

The black skimmer are the only known birds with vertically shaped pupils.   Contributed photo by Mike Williams for The Victoria Advocate

The black skimmer is a fascinating bird.

This medium-sized shorebird has a long body when sitting on its short reddish legs because of its long, pointed wings that span more than 3.5 feet.

In breeding plumage, black feathers cover the back and extend up the nape and over the head like a cap to right below the eyes.

White begins below the eyes and extends across the belly and ventral sides of tail and wings.

In the nonbreeding season, the white below the neck extends up across the nape, giving it a white collar.

Skimmers are the only-known birds with pupils that are vertical slits, like cats'. This is thought to be an adaptation to enhance nocturnal vision - they forage day and night - and to protect their retinas from bright sunlight.

A skimmer's long bicolored bill of bright orange is unmistakable, and it's about half its length from the base then black to the tip.

However, this is no ordinary big, bright bill. Skimmers are the only birds to model a laterally flattened bill, like scissors, with the lower mandible longer than the upper.

The name "skimmer" aptly applies because the bird uses this unique bill to skim for its meals.

The skimmer is incredibly graceful in flight. Just inches above shallow stillwater, the submerged lower mandible - rich in nerves - cuts through the water like a knife to snap up small fish. Upon contact with the small fish, the shorter upper mandible closes down on the prey. If the mandibles were equal in length, this strategy wouldn't work.

Picking up food from the ground by an adult skimmer is rarely observed; however, skimmer chicks, which have equal-sized mandibles, regularly eat fish dropped on the ground by their parents and only develop adult bill proportions toward fledging age.

The black skimmer is found along the coasts of the eastern and southern U.S., Mexico and Central America and on rivers and wetlands across much of tropical South America.

Skimmers are grouped with gulls and terns in the family Laridae. They are colonial ground nesters, often found with other nesting colonial shorebirds on sand and shell-covered beaches. Black skimmers are not doing well at many of their nesting grounds throughout the U.S. and in Texas.

Colonial waterbird surveys show a 70 percent decline in breeding birds during the past four decades. Threats include habitat loss, nest predation and anthropogenic disturbances.

However, one huge Texas skimmer success story began in a parking lot in the late 1960s, when employees at the Dow Chemical Company in Freeport noticed a few pairs of skimmers nesting in their lot.

The Dow Skimmer Colony has grown to about 1,280 nesting birds - among the largest colonies in Texas - where Dow has set aside the lot for the skimmers, complete with protective fencing and hotwire.

The Gulf Coast Bird Observatory biologists monitor the breeding colony each year in collaboration with Dow and support from the American Bird Conservancy and National Fish and Wildlife Foundation.

Presented just a week ago at the Texas Colonial Waterbird Society meeting were initial results from a study being conducted by David Newstead and Owen Fitzsimmons with the Coastal Bend Bays and Estuaries Program in Corpus Christi.

These scientists try to identify the annual spatial and habitat-use patterns of Texas black skimmer, for which there is little to no information.

This past summer, scientists set up satellite transmitters to 10 black skimmers captured along the coast. The scientists now sit back as the location data beam down to their computers.

Data from seven birds illuminate two general patterns.

Three of the birds spent the breeding season in Texas or Louisiana, wintering along the Texas Gulf Coast. Four of the birds left the Texas coast from early June to mid-October and traveled to the Gulf coast of Veracruz, Mexico. They then moved across the isthmus to the Pacific coast of Honduras (three birds) and Acapulco (one bird), where they are wintering.

Not much is known yet about the protection status of these international sites, but this research - a cooperative agreement with the U.S. Fish and Wildlife Service with support from ConocoPhillips - is continuing.

So stay tuned to what more will be learned about wintering sites and movement patterns of these magnificent birds.

Robin Bjork is an Avian Conservation Biologist at the Gulf Coast Bird Observatory. The GCBO is a nonprofit organization dedicated to saving the birds and their habitats along the entire Gulf Coast, and beyond into their Central and South America wintering grounds.


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