Ibises are a group of long-legged wading birds found in the warmer parts of the world. There are about 30 different species of ibis, with some notable examples being the sacred ibis, scarlet ibis, and white ibis. Ibises can be identified by their characteristic long, downward-curved bills which they use to probe mud and sand for food.
In North America, the white ibis and scarlet ibis are regularly observed. The white ibis has a wide range across the southern United States, Mexico, Central America, and the Caribbean islands. The scarlet ibis has a more restricted range in South America and coastal areas of Central America. This raises the question – are ibises actually native to North America, or were they introduced more recently?
Origin of Ibises
Ibises are part of the ibis and spoonbill family Threskiornithidae. This family originated approximately 45 million years ago during the Eocene epoch. For most of their existence, ibises were found predominantly in the Old World. Fossil evidence indicates that ibises lived across Europe, Asia, and Africa since prehistoric times.
Most species of ibises likely evolved in the Old World tropics of Africa, Asia, and Australia. From there, some species later dispersed to other parts of the world. The evolutionary history and phylogeny of ibises indicates an Old World, not New World, origin for most species.
Fossil Evidence in North America
There is fossil evidence that ancient extinct species of ibises lived in North America millions of years ago. A 2018 study analyzed fossil specimens from the Late Pleistocene epoch, between 126,000 and 12,000 years ago. These fossils were found in deposits across Florida and the Carolinas.
The study concluded that two previously undescribed ibis species inhabited these areas during the Pleistocene. These extinct species were named Eudocimus sivan and Eudocimus wintoni. Another earlier extinct species, Plegadis pharangites, lived in North America 5-2 million years ago during the Pliocene.
While ancient ibises did populate North America prior to modern times, these species all became extinct thousands or millions of years ago. They likely died out during one of the ice ages and are not direct ancestors of today’s ibises.
Range Expansions by Modern Species
The modern species of ibises found in North America today, like the white ibis and scarlet ibis, are relative newcomers. The historical ranges of these birds were limited to the tropics and subtropics. In the last few centuries, their ranges have expanded northward into North America.
For the white ibis, this expansion occurred naturally as the birds spread along the Atlantic and Gulf coasts. Scientists believe that the scarlet ibis was introduced to coastal areas of Central America and the Caribbean islands by humans. From these introduced populations, they expanded their range into the southeastern US.
Neither the white ibis or scarlet ibis have fossil records in North America dating back more than a few hundred years. All available evidence indicates that today’s ibises arrived in North America through range expansions from tropical populations. They are not descended from any ancient North American lineages.
History in the Americas
If ibises are not native to the Americas, when did they originally arrive? Historical records can provide clues. One of the earliest documented observations of ibises in the Americas comes from Columbus’ 1494 voyage. Upon reaching the island of Hispaniola, Columbus recorded seeing “white birds with long legs like cranes.” These were almost certainly white ibises.
Other early Spanish explorers also documented ibises in the Caribbean. When the Spanish arrived in Mexico in the 1500s, they did not record seeing any ibises. Scarlet ibises were first noted along the Central American coast in the 1700s. Based on this history, it appears ibises only started inhabiting coastal areas of North and Central America within the last few centuries.
Habitat Suitability
The recent range expansions of ibises into North America also correspond with habitat changes caused by human activity. Ibises thrive in wetland environments, particularly shallow saltwater coastlines. Beginning in the 1700s, coastal development significantly transformed shoreline habitats along the Atlantic and Gulf coasts.
Activities like wetland clearing, dam construction, and shoreline development created new habitat favorable to ibises further north than their historical range. This allowed both white and scarlet ibises to spread northward from their core ranges in the topics over the last 250 years. Human changes to coastal wetlands opened up new habitat for ibises to colonize.
Conclusion
Based on all available evidence, ibises do not appear to be native species with an evolutionary history in North America. Fossil records show ancient extinct ibises inhabited the continent millions of years ago. However, the modern species observed today originated in the Old World tropics.
Within just the last few centuries, these ibises have expanded their ranges into North and Central America following habitat changes caused by human activity. While ibises are now well-established across many regions of North America, they did not evolve on the continent or inhabit it through prehistoric times. Technically, the white ibis and scarlet ibis are recent newcomers, native to the tropical Americas but introduced to temperate North America.
Ibis Species | Native Range | Arrival in North America |
---|---|---|
White Ibis | Tropical Americas | 1700s – Natural range expansion along Atlantic and Gulf coasts |
Scarlet Ibis | South America | 1700s – Introduced to Central America and Caribbean islands, later natural range expansion into southeastern US |