A Laughing Gull flies along the waterfront in Mobile, Alabama, in late July. Photo by Carrol Henderson
We've all seen the horrific photos of birds and other wildlife in the Gulf of Mexico covered in oil, but new photos from our longtime friend and contributor Carrol Henderson suggest a more insidious impact of the disaster on birds that have been partially oiled but not immediately doomed.
Henderson, the nongame wildlife program supervisor for the Minnesota Department of Natural Resources and the author of many books, photographed Laughing Gulls, Brown Pelicans, Royal Terns, and Sandwich Terns on July 21 and 22 while he was attending a meeting of the Mississippi Flyway Council in Mobile, Alabama.
After he returned home and studied his photos, he realized something was wrong with some of the Laughing Gulls in his pictures.
"I noticed that there were some gulls with very degraded tail feathers and secondaries," Henderson says. "The vanes of the feathers were missing along the tips. I have photographed many species of gulls in many countries in the past 20-plus years, but I have never observed this pattern of plumage degradation before. It does not appear related to the molt patterns of gulls, because they typically lose matching feathers from both wings in synchrony."
"Perhaps I am overly suspicious of oil-spill impacts," he continues, "but I believe this could be the result of the vanes breaking off the feather shafts because of excessive preening after the feathers have been exposed to oil residue."
The photo at the top of this post shows a Laughing Gull in normal breeding plumage. Below are Henderson's photos showing other gulls with degraded feathers.
This gull's tail feathers are degraded so much that the vanes are missing from either side of the central shafts.
On this bird, the secondaries — the feathers on the trailing edge of the wing — appear to have been stripped.
On this gull, the tail and secondary feathers appear to have been stripped.
In this shot, Henderson noticed a "suspicious brown residue on the bill." It is concentrated at the back of the bill and may be a mixture of oil and sand.
Henderson says he has heard anecdotally that other waterbird species in the region have similarly degraded feathers, but he noticed it only on Laughing Gulls.
"I am curious to know if this may be a sublethal effect of the oil spill on waterbirds that has not been widely reported up to this point," he adds. "Since Laughing Gulls are mainly scavengers, they do not depend on a high degree of aerial agility for foraging. I routinely see Laughing Gulls along the coasts of Costa Rica each winter. I don't know how significantly such feather damage could affect migration success. If these impacts occurred on terns, for example, it could affect their foraging effectiveness and migration abilities."
Henderson says that if it's common for birds to preen excessively after being oiled, "it could have long-lasting consequences for birds wintering and migrating through the Gulf this fall and winter." Because he works to conserve birds in Minnesota, he's most concerned about species that breed in the Midwest and migrate to the Gulf, including Common Loon, Lesser Scaup, Western Grebe, American White Pelican, and Redhead.
The Laughing Gull, a common year-round resident of the Gulf and Atlantic coasts, is abundant and therefore not high on anyone's list of birds to be most worried about due to the oil disaster. (For example, birder, author, and birding-tourism expert Ted Eubanks omitted the Laughing Gull from his list of 25 species threatened by the BP fiasco. He included Franklin’s Gull, Least Tern, Black Tern, Royal Tern, and Black Skimmer.)
Even though the Laughing Gull has a lower priority than most birds, the disaster still has had an effect on the species. The Houma Courier in Houma, Louisiana, reported on Thursday, July 29, that gulls are scavenging at an oyster-processing plant, a behavior that one employee hasn't witnessed in his 40 years on the job. Melanie Driscoll, director of bird conservation for Audubon's Louisiana Coastal Initiative, tells the paper that many gulls are heading inland to find food.
"There's a sense that the gulls may be hungry because they basically had a buffet [from fishing operations along the shore], and now it's no longer there," Driscoll says.
In this shot, a Laughing Gull carries a chicken finger that it picked up in a park. Look closely at its wings. A few of its secondaries show signs of excessive preening. Henderson notes that a species that is so often taken for granted "may have tipped us off on another impact to watch for." --Matt Mendenhall, Associate Editor
All photos by Carrol Henderson
Gulf-area birders: If you see or photograph birds with degraded feathers similar to the gulls Carrol Henderson photographed, please report them to eBird and to Daniel Poleschook of the BioDiversity Research Institute.
Gulf oil spill: What you can do
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