Birds Of A Feather, Mexican Bird(s) Of The Month: Three Who Don’t Mind Getting Their Feet Wet

By Dennis Taylor

If you happen to walk along the banks of the Presa in El Charco when it’s full of water, or the shores of Presa Allende where the water is shallow, you will almost surely see one, if not all three, different types of wading birds.

The White-faced Ibis, American Avocet, and Black-necked Stilt all share the same habitat and have long skinny legs (good for wading). But that’s the extent of their similarities.  Aside from their divergent plumages, you will note right away the differences in the shape of their beaks.

The largest of the three, the White-faced Ibis (Plegadis chihi) sports a large, downward curved, sickle-shaped bill.  It thrusts its strong beak deep into the mud or soft soil and probes for hidden prey like worms, small crustaceans, insect larvae, and other invertebrates.  From a distance, it looks uniformly dark, but through binoculars in good light, spot stunning, iridescent colors:  deep maroon, emerald, bronze, and violet. The name-sake white mask around its ruby-red eyes and bill is only apparent during breeding season.

México is home to two other Ibis species, the White Ibis (Eudocimus albus), and the Glossy Ibis (Plegadis falcinellus), but their range is not as extensive as the White-faced Ibis which covers the entire country.  In México, the White Ibis dwells along eastern and western coastal areas, while the Glossy Ibis is concentrated around seashores in the Yucatan Peninsula. The White-faced and the Glossy are large, iridescent purple-bronze-colored birds with long, gray sickle-shaped beaks.  The only way to tell them apart is by eye color: ruby red for the White-faced Ibis, and dark brown for the Glossy. The White-faced Ibis is found only in the Americas, but the Glossy Ibis also lives across Eurasia, Africa, and Australia.  It is thought that the White-faced Ibis evolved following an early colonization of the Americas by the Glossy Ibis.  Since their ranges overlap in some areas, hybridization is possible, making certain identification in these areas even more difficult.

The next wader is the intermediate-sized American Avocet (Recurvirostra americana) with an extensive range covering most of México, including the northwestern United States and south-central Canada, where it breeds. Interestingly, female American Avocets sometimes lay their eggs in the nest of another female (called “brood parasitism”) who incubates them without noticing.

The American Avocet has a black-and-white body and a rusty head and neck. As it glides along through the shallows on its long, bluish-gray legs, it swishes its slender, up-curved bill from side to side just below the water’s surface or across the top layer of mud to catch tiny crustaceans and insect larvae.  This behavior, called “scything” or “sweeping” is quite effective for its bill with an upward curvature which prevents it from digging too deeply into the mud while sweeping.

The last of the trio is the Black-necked Stilt (Himantopus mexicanus). This elegant little wader seems to be dressed for a white-tie event in its distinctive black and white plumage. Unlike the curved bills of the previous two, the Black-necked stilt’s bill is jet-black, sharp and straight as an arrow. Like the previous two, they have an extensive range throughout México and large areas in southern regions of South America.  They breed mostly in the northwestern United States.  Like the American Avocet, female Black-necked Stilts also practice brood parasitism, preferring to lay their eggs in the nests of American Avocets.

When they hatch, the adoptive mother birds rear the hatchlings as if their own.  Black-necked Stilts and American Avocets belong to the same family (Recurvirostridae), and are capable of hybridizing and producing young.  However, hybrid offspring, nicknamed “avo-stilt,” are rare.

The long, rose-pink legs of Black-necked Stilts are the second-longest in proportion to their bodies of any bird (exceeded only by flamingos).  Their bill shape allows them to use a different strategy for obtaining food as they wade through the shallows or walk across mud flats.  The Black-necked Stilt is a visual hunter, and it most often simply pecks or snatches prey from the surface of the water or mud.  Their straight bill is ideal for quickly catching and grasping individual aquatic insects, small fish, tadpoles and snails that it sees just below the surface.

These three waders, often seen working side-by-side in shallow, muddy waters, can non-competitively use the same habitat because their distinctive bill shapes allow them to employ uniquely different methods for obtaining their food from this source.