The white ibis (Eudocimus albus) and the glossy ibis (Plegadis falcinellus) are two very similar looking wading bird species found in North America. Both belong to the ibis family Threskiornithidae. At first glance, they appear almost identical with their long downward curving bills, long legs, and overall white plumage. However, there are some key physical differences between these two bird species.
In this article, we will compare and contrast the white and glossy ibis in terms of physical features, habitat and range, diet, breeding behaviors, conservation status, and more. Learning how to distinguish white and glossy ibis is important for birders and ornithologists studying these species in the wild. Read on to become an expert at telling these two ibises apart!
Physical Features
While white and glossy ibises share many physical similarities, careful observation enables one to distinguish between them.
Size
White ibises are slightly larger than glossy ibises. White ibises reach lengths of 22-32 inches, compared to 20-28 inches for glossy ibises. Wingspans range from 35-43 inches in white ibises and 31-38 inches in glossy ibises. On average, white ibises are about 10% larger than glossy ibises. The size difference becomes apparent when seeing the two species together.
Bill
Both species have long, curved bills used for probing in muddy wetlands. However, the bills differ slightly in length and color. White ibises have olive-colored bills that measure a bit longer in proportion to their body size. Glossy ibis bills are darker greyish-brown and average slightly shorter than white ibis bills.
Plumage
As their names suggest, white and glossy ibises have predominantly white plumage. However, glossy ibises appear darker and shinier due to dark green and purple iridescence overlaying their white feathers. The wings have a bronzy iridescence. White ibises lack this glossy sheen. Their white feathers are pure white, with black wingtips. During breeding season, white ibises develop orange bills and facial skin, while glossy ibises retain their year-round bill and facial colors.
Legs
Both species have grey-black legs. But white ibises tend to have brighter pink-red feet, while glossy ibises have duller brownish-red feet.
Eyes
White ibises have dark brown eyes, while glossy ibis eyes are red.
Habitat and Range
White and glossy ibises occupy overlapping but distinct habitats and ranges. Understanding where each species lives helps with identification.
White Ibis
White ibises live year-round in the coastal southeastern United States from North Carolina to Texas. Their range extends along the Gulf Coast through Mexico and down into Central America. White ibises inhabit coastal marshes, tidal pools, wet prairies, mangrove swamps, lake edges, and flooded fields. They forage in shallow wetlands.
During summer, some white ibises migrate north along the Atlantic Coast up to South Carolina. But the core range resides in the southeastern states.
Glossy Ibis
Glossy ibises have a more widespread distribution across the Americas. Their breeding range extends across the southern U.S. from California to Virginia. They also breed along the Gulf Coast, Caribbean islands, and in scattered inland wetlands.
Glossy ibises winter primarily along the Atlantic and Gulf Coasts, as well as in Central and South America. In winter, they vacate the northern parts of their range and migrate south.
Unlike white ibises, glossy ibises frequent both freshwater and saltwater habitats. They forage in estuaries, marshes, ponds, flooded fields, and shorelines along rivers and lakes.
Range Overlap
During winter, the ranges of white and glossy ibises overlap extensively in the southeastern U.S. Both species occur along the Gulf Coast wetlands at this time of year. Farther north, glossy ibises predominate. In summer, glossy ibises vacate the Deep South, migrating north of the core white ibis range.
Diet
White and glossy ibises forage on very similar prey, even eating alongside each other frequently in coastal wetlands. Their diets consist predominantly of small aquatic invertebrates.
White Ibis Diet
– Insects – especially grasshoppers, dragonflies, damselflies
– Spiders
– Snails
– Crustaceans – including crayfish and crabs
– Aquatic worms
– Small fish and frogs
– Occasionally small snakes and lizards
Glossy Ibis Diet
– Insects – beetles, flies, moths, mayflies, grasshoppers
– Crustaceans – small crabs and crayfish
– Snails
– Fish
– Frogs and salamanders
– Small rodents – mice, shrews, voles
Both ibises probe through mud with their long bills to feel for prey hidden below the surface. They also pick insects and other prey items off vegetation and the water’s surface. Their diets are very flexible based on locally abundant food sources. Generally white and glossy ibises consume very similar foods in any given wetland foraging habitat.
Breeding
During the breeding season, white and glossy ibises nest in large colonies with other wading birds. But some key differences exist in their nesting habits.
Breeding Trait | White Ibis | Glossy Ibis |
---|---|---|
Nest Location | Trees or bushes over water | Marsh vegetation, reedbeds |
Nest Description | Stick platform nests | Bundles of reeds and grasses |
Clutch Size | 2-5 eggs | 3-5 eggs |
Incubation Period | 21-25 days | 21-24 days |
Fledging Period | 35 days | 28 days |
Key points:
– White ibises build nests in trees and bushes, while glossy ibises nest on the ground in marsh vegetation.
– White ibis nests are sturdier stick platforms, whereas glossy ibis nests are looser bundles of reeds/grasses.
– Clutch sizes are similar, but glossy ibis chicks fledge faster than white ibis chicks.
The nesting habits reflect the preferred habitats of each species, with white ibises nesting in and around trees in coastal swamps, and glossy ibises nesting in reedbeds in marshes.
Conservation Status
Both white and glossy ibises experienced population declines in the late 19th and early 20th centuries due to hunting, egg-collecting, and habitat loss. Conservation actions have enabled recoveries of both species:
White Ibis
White ibises are classified as Least Concern by the IUCN Red List. Populations rebounded from around 5,000 breeding pairs in the 1930s to over 150,000 today. They remain common throughout their coastal range.
Glossy Ibis
Glossy ibises are also Least Concern. The global population consists of at least 270,000 individuals. Numbers crashed early in the 20th century but resurged with protective legislation. Threats include wetland drainage and contaminants.
Ongoing wetland conservation will help ensure healthy populations of both ibises. Neither species is considered endangered, but monitoring is needed to detect any new declines.
Conclusion
In summary, white and glossy ibises share many similarities but can be distinguished by their size, bill color, eye color, plumage iridescence, leg color, breeding habitats, and ranges. Remember these identification tips:
– White ibises are slightly larger and have bright pinkish feet.
– Glossy ibises have darker bills and iridescent plumage.
– White ibises nest in coastal swamp trees, while glossy ibises nest on marsh floors.
– White ibises live year-round along the Gulf and southeastern Atlantic coasts.
– Glossy ibises range more widely across North America.
Equipped with this knowledge, bird enthusiasts can readily tell apart these two elegant wetland birds. Both species fill important roles in coastal ecosystem food webs across the Americas.