CLEAR BLUE WONDER

Pelagic Tern
Bridled Tern
Brown Booby
Pelagic Tern

Far Off The Louisiana Coast, Pelagic Birds Thrive In The Gulf Of Mexico

story by Robert Dobbs, LDWF Non-game Ornithologist

 

Undoubtedly, you’ve heard the phrase out-of-sight, out-of-mind. That would be a good way to describe pelagic birds, including some species found off the Louisiana coast.

 

Pelagic birds, simply put, are seabirds that spend most of their lives on the open ocean with many species coming to land only for a few weeks each year to nest. The pelagic environment may appear as a featureless landscape to the human eye. If you’ve ever been on a cruise in the Gulf of Mexico, you’ve likely noticed what appears to be nothing but blue water once you get away from the coast.

 

But currents, thermoclines, upwellings, and other marine forces are constantly changing and shifting, thus creating a dynamic and diverse mosaic of variation in food availability, water temperature, salinity, and other factors that collectively influence the distribution, behavior, and ecology of pelagic birds.

 

Pelagic birds are among the most poorly known birds in the world, as they are difficult to find, much less follow and observe, in the vastness of the open ocean.

 

Despite the human presence offshore in Louisiana, where oilfield infrastructure and fishing boats are common sights in nearshore waters, pelagic birds are typically confined to deep, blue water beyond the edge of the continental shelf.

This area is largely inaccessible to most people, including birders and ornithologists. Although birding and ornithological exploration trips occasionally venture far offshore, those efforts have simply not provided enough coverage to gain a good understanding of the status and distribution of pelagic bird species.

 

In addition, variations in water quality and water clarity, influenced by the strength and position of dynamic currents such as the Gulf of Mexico loop current, as well as the flow of freshwater entering the Gulf of Mexico from the mouth of the Mississippi River, further complicate our understanding of pelagic bird distribution.

 

The vast majority of pelagic birds occur in blue water, which is typically 40-60 miles south of the mouth of the Mississippi. However, during periods of low river flow, blue water may be as close as 20-30 miles from the river mouth.

 

Another factor that influences where pelagic birds occur is the continental shelf. The width of the continental shelf varies dramatically south of the Louisiana coastline. The shelf is very wide in the western part of the state and narrows dramatically heading east. Thus, deep water is much closer to the shoreline below the mouth of the Mississippi River than anywhere farther west in the state. This almost certainly influences the distribution of pelagic birds off our coast; not surprisingly, the vast majority of pelagic bird exploration occurs off the mouth of the river, further biasing our understanding of the status and distribution of these species.

 

Pelagic birds spend most of their time foraging, often flying long distances in search of food resources. When not foraging, many species will loaf and, presumably, sleep on the water or while perching on floating marine debris. Some pelagic birds are even known to sleep while flying. Recent work shows that great frigatebirds may regularly sleep for extremely short periods of time - up to 10-seconds - while soaring upward on thermal updrafts.

 

So what are some of the pelagic bird species seen south of Louisiana’s coastal waters? Let’s take a look:

 

Pelagic Bird Species

  • Tubenoses - These are the ultimate pelagic seabirds, characterized by numerous adaptations for life at sea. This group includes the petrels, shearwaters, storm-petrels, and albatrosses.

Their nostrils are enclosed within tube-like structures at the base of their bills. Adapted to consume salty prey and saltwater, tubenoses have salt glands above their eyes that remove the salt from their bloodstream, excreting it in a concentrated solution out of the nasal passages. Unlike most birds, tubenoses also have well developed olfactory senses, which allows them to find food in the vast expanse of ocean and to recognize their individual nesting burrows among those of their neighbors in dense colonies.

Nine species of tubenoses have been documented off the Louisiana coast, including five species of shearwaters, three species of storm-petrels, and one albatross.

Shearwaters are medium-sized to large seabirds that have long, pointed, narrow wings and relatively short, often graduated, tails. Shearwaters fly by alternating stiff wingbeats with long, seemingly effortless glides and land on the water to forage by taking prey from the surface or by diving.

Cory’s and Audubon’s shearwaters appear to occur regularly off the Louisiana coast during the summer to early fall months. Great shearwater is considerably less common (about 10 accepted records), followed by sooty shearwater (two records) and Manx shearwater (one verified record).

Storm-petrels are small, robin-sized, seabirds that flutter at the ocean surface, often appearing to dance with their feet touching the water, picking small prey items from the surface of the water. Their foraging strategy and delicate build set them apart from shearwaters.

Three species of storm-petrels have been documented in waters off Louisiana: Wilson’s, Leach’s and band-rumped. They are most often detected from late spring through summer. Status, distribution, and timing of occurrence in Louisiana are not well known for any of these species, but Wilson’s appears to be the most common and Leach’s the least common.

A yellow-nosed albatross photographed just off Holly Beach in May 1970 represents the sole record of any albatross in Louisiana waters and one of only a handful of records in the Gulf of Mexico.

  • Tropicbirds - Highly pelagic during the nonbreeding season, red-billed tropicbird is one of the rarest pelagic birds off the Louisiana coast, where it has been documented on four occasions.
  • Terns - Terns, in general, are common birds along the Louisiana coast and in nearshore waters, and most are not pelagic. However, two tropical breeding species - sooty and bridled terns - are highly pelagic during the nonbreeding season. These species may be found foraging along mats of sargassum in blue water or perched atop flotsam trapped within the mats. These terns are among the most likely pelagic species to be detected inland during hurricanes and tropical storms.
  • Boobies - Masked, red-footed and brown boobies are three tropical-breeding species that rarely occur in Louisiana pelagic and nearshore waters. The masked booby was once the most commonly observed booby in Louisiana. However, in recent years, the brown booby has ventured inland with surprising regularity and may surpass masked booby sightings. The red-footed booby is exceptionally rare, having been documented only three times in the state.
  • Frigatebirds - The magnificent frigatebird is a large, conspicuous bird that occurs in both pelagic and nearshore waters and may be seen regularly along the immediate coast and in coastal bays, particularly in southeastern Louisiana.
  • Jaegers - Pomerine, parasitic and long-tailed jaegers are piratic and predatory seabirds closely related to gulls. Unlike most gulls, jaegers are highly pelagic during the nonbreeding season. Jaegers may also be found in nearshore waters as they steal food from gulls and terns that feed behind shrimp trawlers. Pomerine and parasitic jaegers occur regularly in our waters, but only six records of long-tailed jaeger exist for Louisiana.
  • Phalaropes - Unique among shorebirds, Red-necked and red phalaropes are highly pelagic during the nonbreeding season. The vast majority of shorebirds avoid the open ocean, except to migrate over it in long, non-stop flights. In fact, the third species of phalarope, Wilson’s phalarope, is not at all pelagic. Like most species discussed here, the status and distribution of red-necked and red phalaropes off the Louisiana coast are not known, but a recent trip documented approximately 60 red-necked phalaropes associated with sargassum in the Gulf’s deep, blue water.

 

 

Storm Birds

Hurricanes and tropical storms offer birders the rare and unique opportunity to occasionally find pelagic birds inland. These tropical cyclones regularly entrain pelagic birds at sea and then deposit them inland, sometimes very far inland, after making landfall. Once they find themselves in the unfamiliar terrestrial landscape, pelagic birds often seek out large inland lakes or major rivers, which they may follow back south to the Gulf.

 

Although most storm birds tend to be common coastal gulls and terns, pelagic species such as sooty tern and magnificent frigatebird also turn up regularly. On exceptionally rare occasions, a shearwater or storm-petrel may be found inland. In fact, the only two accepted Louisiana records of brown noddy, a tropical pelagic tern, occurred following Hurricane Carla in September 1961.

 

Of course, any attempt to look for birds during or following a hurricane or tropical storm should only occur after safety concerns have been alleviated.

 

There is still much to learn about pelagic birds. The Louisiana Department of Wildlife and Fisheries encourages the public to submit photographs and details of observations of pelagic birds at sea.

 

 Additional Information

To learn more and to submit information about observed pelagic birds, contact Robert Dobbs at rdobbs@wlf.la.gov.

WINTER 2020