September and October are traveling times for many bird species. Most of the travelers are southbound migrants: stragglers from the shorebird migration that peaked in August; the songbird wave that crests during September; then the kettles of hawks and rafts of waterfowl that start to appear late in September and increase through October.
But the summer dispersal of Gulf Coast wading birds—primarily herons and egrets—continues into the warm months of autumn, too. So, in Austin, birds can be moving westward rather than southward into our area.
And some, such as White-faced Ibises, may do both. You can often find a group of these dusky, long-legged, long-necked waders at Hornsby Bend early in the fall. Their odd yet elegant form culminates in the sickle-shaped bill that inspired the folk name of “black curlew.”
But don’t count on seeing the “white face.” The white feathers that surround the bare facial skin are a feature of the breeding plumage of adults, not seen on the juvenile birds or post-breeding adults. Autumn White-faced Ibises are also less likely to show any of the rich maroon-chestnut hues on the head and body feathers, though the wings and back retain their green and bronzy sheens.
They may look like a cross between herons and curlews, but ibises are not very closely related to either group. From DNA analysis, their nearest relatives, despite very different bill shapes, appear to be the spoonbills, followed by the storks. An old family of birds, the ibises also have a very long history of association with humans—as their names attest. “Ibis” is the only North American bird name (to this writer’s knowledge) that can be traced directly to ancient Egyptian. (Not always pronounced correctly, the first “i” is long, so pronounced “EYE-biss.”) The unwieldy family name, Threskiornithidae, translates from the Greek as “sacred bird.”
The ancient Egyptians attached great religious significance to the ibis. The origin of this connection is not clear, though the Greek writer Herodotus related a tale of ibises devouring a swarm of “winged snakes” that invaded Egypt from the mountain passes. (What these invaders actually were is open to question. They may have been locusts, which are frequently eaten by ibises.)
The Egyptian god Thoth—god of the moon, wisdom, and secret knowledge—is usually represented by an ibis in hieroglyphics. It may be that the crescent-shaped ibis bill led to associations with the crescent moon, and the lunar deity.
Though other ibis species are present in Egypt, the Sacred Ibis (Threskiornis aethiopicus) was the one linked with the deity. One might think association with a god would be a good thing for a bird species, and it seems that wild Sacred Ibises were protected from harm by pharaonic decree. However, ibises were also raised for the purpose of ritual sacrifice and mummification to curry favor with Thoth. Archaeologists estimate there are hundreds of thousands of mummified ibis remains still buried in underground Egyptian vaults.
Given this history, White-faced Ibises are probably lucky that they were not so revered. However, human activities have not always been kind to this species, either—especially our penchant for draining wetlands and spraying pesticides.
The bill of an ibis is well-adapted for probing mud or shallow water for the small animals that live there. Crayfish, aquatic insects (especially larvae of flies, beetles, and dragonflies), earthworms, leeches, snails and other shellfish, frogs, and small fish are all important food items. The tip of the bill is sensitive to touch, a particularly useful characteristic for feeding in murky water or mud. The long legs, paired with the long neck and bill, allow an ibis to probe the bottom sediments of pools to about eight inches below the water surface without submerging the rest of its body.
The most widespread ibis species in North America, White-faced Ibises have nested from Oregon to Alberta and Minnesota, south to California and Texas, and east along the Gulf of Mexico at least to Alabama. They also breed in parts of central Mexico. There is, intriguingly, also a large and completely separate population in southern South America, ranging from Peru to Argentina.
In the winter, White-faced Ibises of the interior West migrate south to Mexico, a few locations in southern California and Arizona, and the Gulf of Mexico coast, especially in Texas and Louisiana.
Though the North American breeding range is large, White-faced Ibises breeding in the interior West are nomadic, and do not always nest in the same place every year. Parent ibises need to be able to collect a lot of food quickly in order to raise a family. The shallow marshes and flooded fields where they forage are often rich in food resources, but those wetlands can disappear from one year to the next after drought or a change in land management. So the birds need to be flexible, and to explore widely to find a suitable breeding location.
When they do find a wetland that provides enough food for one pair, it is often rich enough to support several ibis families for the duration of the breeding season. So White-faced Ibises can afford to be colonial nesters. They are often found in groups, which provide greater protection from predators. Like neotropical migrants that migrate from the tropics to nest in the forests and prairies of temperate North America, they are opportunists: reaping a harvest that is bountiful for a limited time.
Draining natural wetlands to convert them to cropland has, of course, been detrimental to White-faced Ibises. Human-created rice fields have compensated for that loss in some areas, especially on the Texas and Louisiana coastal plain. They provide large expanses of shallowly-inundated wetlands, perfect for finding crayfish. Irrigated fields can also provide a substitute habitat for them, partially offsetting the draining of wetlands, though ibises abandon these when pools of water evaporate.
Unfortunately, dieldrin, sprayed to control insects in the rice fields, led to the deaths of nestling and juvenile ibises as the birds accumulated the poison in the brain and other body tissues. Harry Oberholser, in his Birds of Texas account of the species, relays a report that a colony of more than 1000 adult White-faced Ibises at Lavaca Bay raised almost no young in the summer of 1970. Elsewhere, control of mosquitoes with DDT led to the same weakened eggshells among ibises, and subsequent nest failure, as it did for Bald Eagles and Ospreys.
Between the loss of natural wetlands and the poisoning of artificial ones, White-faced Ibis numbers plummeted in the mid-1960s and early 1970s. Banning dieldrin, DDT, and related chemicals in this country has certainly helped their reproductive success. Further loss of wetlands from the arid West will continue to be a danger, especially as demand for water increases in that region.
As with the survival of so many animal species, ensuring that the “black curlews” continue to make their autumn appearance at Hornsby Bend—from whichever direction they come—will depend upon the decisions we make in conflicts between their needs and the wants and needs of our growing human population.