HOUSTON CHRONICLE (Texas) 10 July 03 Study examines alligators' diets to determine their impact on mottled ducks (Shannon Tompkins)
Matagorda County's coastal marsh woke to a typical steamy summer day.
Thunderheads boiled back over the Gulf, their cotton-clump forms smeared red and purple, gold and black/blue by the fractured light of the late June dawn.
Against that backdrop, knots of birds painted moving, noisy silhouettes over the rich wetlands.
A band of ibis sifted down and into the thin water, joining a gathering of wood storks, great blue herons, black-bellied whistling ducks cattle egrets and snowy egrets. The conglomeration of long-legged wading birds stalked the inches-deep flat, probing and poking for food.
In the deeper, open areas and in the edges of the vegetation floated the low, dark forms of mottled ducks, the Gulf Coast's endemic waterfowl.
Beyond the ducks and looking to the casual observer like nothing more than a piece of floating vegetation was the distinct silhouette of an alligator. Just the tip of the nose and that brow holding those slit-irised reptilian eyes rose above the water.
The alligator turned toward a roaring hum coming from the other side of the flat. As the spotlight-equipped airboat boat and its occupants closed the distance in the growing light, the gator sank and evaporated, leaving barely a ripple on the surface.
The night's hunt was over, for both the gator and the crew in the airboat.
While the alligator shadowing the mottled ducks in the borrow ditch of the moist soil unit on Mad Island Wildlife Management Area escaped the hands and snares of the Texas Parks and Wildlife Department crew in the airboat, a half-dozen of its relatives had not.
Secured in bags, their snouts wrapped closed with duct tape, the gators resting in the bottom of two airboats were headed back to Mad Island's equipment barn where they would play roles in a study aimed at discovering the reptile's diets.
Such information is crucial to understanding the reptiles and their impact on the natural resources with which they share habitat.
Of particular interest to state wildlife scientists is the impact alligators have on mottled ducks.
"What got this study going was our mottled duck research," said Todd Merendino, TPWD biologist who oversees wetland programs along the middle Texas coast. "We're interested in finding out how much alligators prey on mottled ducks, and if it could have an impact on mottled duck recruitment."
The possibility that alligators are a considerable predator on mottled ducks is a logical theory. Along the coast, the two species often share the same pockets of habitat.
In The Mottled Duck, Texas wildlife scientist Charles Stutzenbaker's seminal 1988 monograph on the Gulf Coast bird, he notes, "The alligator is the single most efficient predator of adult mottled ducks and ducklings."
During intense mottled duck banding efforts over the past few years, TPWD crews collecting molting adult and flightless young-of-the-year birds in the large, shallow open-water lakes and reservoirs the birds use during their flightless stages have seen such predation.
"When we've been out at night collecting molting birds for banding, we've seen gators with mottled ducks in their mouths," Merendino said.
Gators and mottled ducks have coexisted for thousands of years. But man-wrought changes over the past few decades make their interaction of considerable interest to wildlife managers.
Barely more than 30 years ago, alligators had been pushed to the brink of vanishing from much of Texas' wetlands by decades of unregulated hunting and habitat destruction.
But with protection and management, Texas' alligator population boomed through the late 1970s and into the 1980s.
While TPWD gives no statewide alligator population estimate, Texas certainly appears to be home to more than a half-million of the reptiles.
TPWD estimates the gator population in a three-county area of Southeast Texas -- Jefferson, Orange and Liberty -- at about 280,000.
The same coastal wetlands holding those alligators serves as crucial brood-rearing and molting areas for mottled ducks. But unlike alligators, which are thriving, mottled duck numbers have been slipping for decades.
Loss of nesting habitat -- grassy coastal prairie and pasture -- has been a major factor in the mottled ducks' decline. That habitat continues shrinking at an alarming rate.
Mottled duck nesting success has been horrible as the birds are jammed into remaining fragments of nesting habitat where the nests are particularly vulnerable to raccoons, skunks, snakes and other predators. Most years, 75-90 percent or more of nests are lost.
Such high nest failure makes survival of what few mottled ducks that do hatch much crucial to the species' health.
Once hatched, those young mottled ducks along with their moms move to large bodies of water where they feed and grow and develop their first complete set of feathers.
Adult males and adult females that lost their nests join them there in late July. Those adults go through their annual molt, remaining on these water bodies while they are flightless.
The ducks are most vulnerable to alligators during this time. And that's why the TPWD project is concentrating on investigating gator diets in areas where the two species overlap.
During June, TPWD field staff collected alligators from Mad Island WMA near Bay City and J.D. Murphree WMA near Port Arthur. They plan another round of captures in late July, the peak of the mottled duck molt.
Crews in airboats capture the alligators during the night, preferably in the hours just before dawn. Alligators feed mostly at night, so by capturing them just before dawn they are likely to have food in their bellies.
Once captured and secured, the gators are transported to a work area where staff have devised a method for collecting stomach contents.
The reptiles are strapped to a plank to immobilize them, then a short piece of PVC pipe is placed in their mouth, and that is secured with duct tape.
Once the gator is secured, TPWD crews insert a plastic tube down the gator's throat and into its stomach, fill the stomach with water, tilt the animal down into a tub, and one of the staff straddles the gator and squeezes -- hard.
The bloated gator is relieved of its stomach contents, which pour into the tub.
Each gator's stomach contents are then screened from the water and placed in a plastic bag for future analysis.
That analysis will count, identify and categorize every piece -- even the tiniest slivers -- of whatever was in the gator's stomach.
And that information, combined with data on the gator's size, where and when it was captured, what kind of habitat it was in (freshwater, brackish, salt) and other information will add to wildlife managers' knowledge of alligators and how they interact with their ecosystem.
The gators are then measured, sexed, fitted with tags and released.
So what are they eating?
"It seems they'll eat whatever they can grab,"Merendino said. "They are pretty indiscriminate."
Indeed.
The first gator checked that June morning had nothing but a handful of marble-size rocks -- yes, rocks! -- in its stomach.
Other gator stomachs have yielded pieces of wood, shotgun shell wads, fishing corks, and other seemingly indigestible items.
Many of the Mad Island gators held lots of crab shell, a function of crabs being quite abundant in the brackish marsh.
Also, inshore fish -- mullet, sailfin mollies, killifish, sheepshead minnows -- found their way down gator gullets.
One of the gators captured in the freshwater area of Mad Island barfed up a crawfish. And the gators in the freshwater marshes of the Murphree WMA have given up pieces of muskrat.
And there were insects. Dragonfly and damselfly larvae, water boatman, water scorpions and other insect parts not immediately identifiable.
Only one of the 20 or so Mad Island gators checked during June had obvious bird parts in its stomach, but the parts -- feathers -- appeared to belong to an unfortunate ibis or stilt rather than a mottled duck, Merendino said.
The exercise underscores just how opportunistic gators are when it comes to feeding, and how important even the smallest and most unlikely parts of the system fuel its largest predator and the bellwether of wetland health.
Whether that predator is a significant factor in mottled duck recruitment remains a question that only emptying more alligator stomachs seems able to answer.
Study examines alligators' diets ... mottled ducks