Iiwi

What is Iiwi?

The Iiwi (Vestiaria coccinea) is a Hawaiian songbird belonging to the Hawaiian honeycreeper family, Drepanididae. Measuring approximately 15 cm (6 inches) in length, this nectar-feeding bird is characterized by its vibrant red body, black wings with white patches, a black tail, and a distinctive sickle-shaped red bill. It derives its name from its unique, squeaky call, which sounds like “ee-ee-vee”.¹

As a member of the Passeriformes order, the Iiwi is part of a group that evolved in the Hawaiian Islands and is found exclusively in that region. Like many other Hawaiian honeycreepers, the species faces significant conservation challenges due to habitat loss and the introduction of non-native species.¹²

What are Hawaiian honeycreepers?

Hawaiian honeycreepers are a group of related birds belonging to the family Drepanididae, within the order Passeriformes. They evolved in the forests of the Hawaiian Islands and are found exclusively in that region.²

These birds are closely related to cardueline finches, such as goldfinches and canaries. Isolated in the mid-Pacific, they underwent a remarkable evolutionary radiation, diversifying in a manner similar to Darwin’s finches in the Galapagos Islands. Their physical characteristics vary based on their diet:

• Nectar-feeders: Typically possess thin bills and red-and-black plumage.
• Seed/Insect-feeders: Usually have finchlike bills and greenish plumage, often with orange or yellow markings on males.
• Intermediate species: Exhibit traits between these two groups.

Most species range from 10 to 20 cm (4 to 8 inches) in length and feature a troughlike, brush-tipped tongue. Unfortunately, habitat destruction and the introduction of non-native species have led to the extinction of at least 8 of the original 23 species, with most survivors currently endangered.²

Why are many Hawaiian honeycreepers endangered?

Many Hawaiian honeycreepers are endangered or have gone extinct due to a combination of human-driven environmental changes and the introduction of non-native species. The primary factors contributing to their decline include:²⁵

• Avian Malaria: The introduction of mosquitoes in the 1820s and the subsequent arrival of the P. relictum parasite devastated native bird populations that had no prior exposure to the disease. While many honeycreepers retreated to high-elevation forests to escape these mosquitoes, rising temperatures have allowed the insects to reach higher altitudes, further threatening the remaining populations.⁶
• Habitat Destruction: Extensive loss of native forests—often caused by the introduction of non-native mammals like goats, pigs, and sheep—has destroyed critical nesting sites and food sources. For example, the endangered palila relies almost exclusively on the seeds of the mamane tree, which is frequently grazed by introduced herbivores.²⁷
• Loss of Specialized Food Sources: Many honeycreepers evolved to feed on specific plants or insects. The decline of these food sources, such as the overharvesting of koa trees for the akiapolaau or the loss of nectar-producing lobelias, has left specialized species without adequate nutrition.⁷

How did Hawaiian honeycreepers evolve differently from other birds?

Hawaiian honeycreepers evolved through a process known as adaptive radiation, a phenomenon where a single ancestral lineage diversifies rapidly to exploit various unoccupied ecological niches in a remote environment.²⁸

Unlike many other bird groups that face intense competition on continents, the ancestors of the Hawaiian honeycreepers arrived in the isolated Hawaiian Islands and encountered an abundance of available resources. Over time, they diverged into numerous species with specialized physical traits adapted to their specific diets:²⁸

• Nectar-feeders: Evolved thin bills to access nectar from flowers, typically displaying red-and-black plumage.²
• Seed and insect-feeders: Developed finchlike bills for crushing or probing, often featuring greenish plumage.²
• Specialized anatomy: Most species developed a unique troughlike, brush-tipped tongue to assist in feeding.²

This evolutionary path mirrors that of Darwin’s finches in the Galapagos Islands, resulting in a level of morphological and ecological diversity that is rare elsewhere in the world.²⁸