- Mary K. Hanson
- Posted On
Tuleyome Tales: The fascinating and ancient-looking white-faced ibis
NORTHERN CALIFORNIA – Thoth was an ancient Egyptian deity with the head of an ibis, and part of his job was to maintain the universe.
Here in the Berryessa Snow Mountain National Monument region, we have ibises, specifically white-faced ibises (Plegadis chihi), and even though they probably don’t maintain the universe, they do a good job of maintaining their little corners of the world.
Where the birds nest depends on the water levels in their favorite stomping grounds. White-Faced Ibises live in freshwater marshes, tule fields and even irrigated landscapes.
Here, in the early summer months, they gather together in loose-knit colonies (called “rookeries”), build their nests and have their babies. There are several of these rookeries around our region, including one within the city of Woodland.
At the rookeries, you can see that the ibises’ twiggy nests are built at various levels among the tules and shrubs. Nest placement can be a tricky business. If you build low, your nest is shaded by the nests above it, and you’re closer to the water, so the kiddies can step out of the nest and cool their feet if they get too warm.
But building low also means your nest is at the perfect height to get invaded by snakes, raccoons, and other marauders.
It’s not uncommon for garter snakes and even birds like the great-tailed grackle, to infiltrate the nests and eat the eggs and the babies.
At the Woodland rookery, I watched as a female great-tailed grackle tried to sneak in between the tules and behind the adult ibis standing on the nest to grab one of the newborn hatchlings. That seemed to be an uncommonly bold attempt at infanticide to me, but the ibis caught sight of grackle almost immediately and chased it off.
Being ibis parents means you’re on a 24-hour security detail. Usually, the females take the night shift and the males take the day shift.
There’s also a problem with building the nests higher up in the tules and branches of low-lying trees, however. Those nests are then exposed to direct sunlight all day long, and that can be difficult for the summer-born babies who for the first several weeks of their lives can’t get out of the nest or move around much.
Parents in the upper nests often shade their offspring with their bodies and bring them fluids in the form of regurgitated water and food to keep them hydrated, but the heat can still take its toll. The summer’s heat might also play a factor in whether the birds will attempt to have a second brood before the season is over.
The ibises’ eggs are a bright turquoise blue so they’re easy to spot in the nests. Egg laying occurs in the morning hours, and usually the female will lay one egg, skip a day, then lay another egg, up to three or four. Sometimes younger females will lay eggs in more than one nest, so it’s hard to tell what egg actually belongs to whom without DNA testing, but the brooding parents don’t seem to care.
Both White-Faced Ibis parents, who look identical (except for the fact that the male is larger than the female), take turns incubating the eggs and feeding the hatchlings.
Whether the pairs mate for life is unknown, but some pairs seem to stay together through several breeding seasons. They generally eat a mixed diet of insects, worms, frogs and snails, leeches, spiders and crayfish.
It takes the youngsters about five weeks to go from hatching to being able to fly with the flock. When they’re young, the babies have dark bodies with a bald spot on the top of the head, and their dark beaks have pink, yellow or flesh-colored stripes on them.
As they mature, the head feathers fill in and the beak turns a sort of olive-gray. At a distance, mature birds may look black, but their true coloring shows itself off when the sunlight hits them at the right angle. Their plumage is actually a gorgeous mix of glossy, iridescent copper, purple and green. They get their name-sake white faces in the breeding season.
We see a lot of ibises in our region and that’s partly do to conservation efforts. In the past, the use of the pesticide DDT and the outright killing of the birds – a study in the 1960s showed that almost 83 percent of banded white-faced ibises in the state of Utah were shot by humans – were threatening to wipe the species out.
Since that time, DDT has been banned and the white-faced ibis was added to the Migratory Bird Treaty Act list to protect it. Right now, the species is doing fairly well.
The breeding season is almost over in our area, but if you still find nesting birds, please be careful not to disturb them.
When conditions are right, these birds can live for up to 14 years or more in the wild.
Mary K. Hanson is a Certified California Naturalist, author, nature photographer and blogger (https://chubbywomanwalkabout.com/). She also teaches naturalist classes through Tuleyome, a501(c)(3) nonprofit conservation organization based in Woodland. For more information, visit www.tuleyome.org.