Gray-backed Tern (Onychoprio lunatus)

Common Name: Gray-backed Tern

Scientific Name: Onychoprio lunatus
SizeDietRange in HawaiiStatus in Hawaii
12 in. - 145 in.crustaceans and small invertebrates, such as krill and planktonOahu, Maui, and Big islandLeast Concern

The Pākalakala, also known as the Gray-backed Tern or Spectacled Tern, is a seabird that is native to the U.S. state of Hawaii. This species is found in the Hawaiian Islands and is considered a unique and important part of the local biodiversity.

Gray-backed Tern

Appearance

Gray-backed perching
Gray-backed perching | image by Duncan via Flickr | CC BY-SA 2.0

In terms of size, they have a length of about 12-15 inches and a wingspan of about 25-30 inches. They weigh around 7-8 oz.

In terms of color, they have a distinctive black cap and nape, a white face, and a gray back. The upperparts are dark gray and the underparts are white. They have a black bill, legs and feet. The tail is forked and the wings are pointed.

Juveniles have a brownish-gray head, back, and wings and white underparts. The Gray-backed Tern is similar in appearance to the Sooty Tern, but can be distinguished by its gray back, and white underparts.

Diet

Gray-backed Tern primarily feeds on fish and squid. They catch their prey by diving into the ocean from a height, often while in flight. They are known to travel long distances in search of food and have a wide foraging range.

Gray-backed Tern also consume crustaceans and small invertebrates, such as krill and plankton. They have a diverse diet and will eat whatever prey is available, depending on the season and location.

Gray-backed Tern have been observed foraging near the surface of the water, diving for food, and sometimes chasing other seabirds to steal their catch. They have been observed feeding in association with schools of tuna, and are known to follow fishing boats and feed on offal and discarded fish.

Behavior

They are known for aerial acrobatic displays and complex system of vocalizations and displays used for communication. Gray-backed Terns are highly social birds and are often found in large colonies during breeding season. They nest in large colonies on rocky cliffs and sandy beaches.

They breed from April to September, during which time they lay a single egg. Both parents take turns incubating the egg and caring for the chick. During non-breeding season, they are known to migrate long distances, often traveling thousands of miles between breeding and non-breeding sites, foraging for food in the open ocean.

They are also known for their aerial acrobatic displays, which they use during courtship and territorial displays. The displays include aerial chases, diving, and aerial courtship displays, such as hovering and diving in unison with a partner. Gray-backed Terns have a complex system of vocalizations and displays that they use to communicate with each other.

They use a variety of calls and songs to communicate with other birds in their colony, including calls to signal a change in direction while foraging, calls to signal a warning of danger, and calls to signal a change in the location of a food source. Overall, Gray-backed Terns are known for their social behavior, aerial acrobatic displays, complex vocalizations, and displays used for communication.

You may also like:  Common Gallinule (Gallinula galeata)

Nesting

These birds typically breed during the spring and summer months on the main Hawaiian Islands, and on small islands and islets off the coast. Their nests are typically located on rocky cliffs and small islands, and are made from a variety of materials including twigs, grasses, and seaweed. The gray-backed tern is known to be a colonial nester, meaning that they tend to nest in groups or colonies.

Habitat

They are found in tropical and subtropical regions, and breed on islands in the Pacific and Indian Oceans. During the non-breeding season, they are known to disperse over a wide area of the open ocean. In Hawaii, gray-backed terns typically breed on small islands and islets off the coast, as well as on rocky cliffs on the main islands.

Range

Gray-backed tern on coral rubble
Gray-backed tern on coral rubble | image by Forest and Kim Starr via Wikimedia Commons | CC BY 3.0 US

In Hawaii, these birds are known to occur on the main islands of Oahu, Maui, and Big island, as well as on small islands and islets off the coast. They are known to occur in the remote and relatively undisturbed northwestern Hawaiian Islands.

Conservation Status

The Gray-backed Tern is listed as “Least Concern” by the International Union for Conservation of Nature (IUCN) in Hawaii. This means that the species is not considered to be at a high risk of extinction in that region.

Interesting Facts

1. Unique hunting strategy

These birds have a unique hunting strategy, they hover high in the air and then dive steeply to catch fish, often plunging into the water headfirst.

2.  Aggressive behavior during breeding

The Gray-backed Terns are also known for their aggressive behavior during breeding season, they will fiercely defend their nest and territory against any perceived threat, including humans.

3. Distinctive plumage

The Gray-backed Tern has a distinctive plumage, with a black cap, white forehead, and gray back, wings, and tail.

4. They are colonial nester

Gray-backed Terns are colonial nesters, meaning they nest in large groups. They prefer to nest on small islands or rocky cliffs, where they have little competition from other bird species and predators.

5. They have a distinctive vocalization

Gray-backed Terns have a distinctive vocalization, consisting of a sharp, piercing “kree-kree” call. They use this call both to communicate with other members of their colony and to signal their presence to potential mates or rivals.

6. High-speed flying and acrobatic maneuvers

The species is also known for its high-speed flying and acrobatic maneuvers, which help them to catch their prey. They are able to fly at speeds of up to 60 miles per hour (96 km/h) and can make sudden turns and twists in the air to evade predators or capture prey.

Frequently Asked Questions:

How long do Gray-backed Terns live?

Gray-backed Terns have a relatively long lifespan, with some individuals living up to 25 years in the wild.

Are Gray-backed Terns social birds?

Yes, Gray-backed Terns are colonial nesters, meaning they nest in large groups. They are also known for their aggressive behavior during breeding season and they will fiercely defend their nest and territory against any perceived threat.

How do Gray-backed Terns navigate during migration?

Gray-backed Terns are able to navigate using a combination of visual landmarks, the earth’s magnetic field, and the position of the sun during their annual migration. They fly over the open ocean, and are able to find their way to their breeding and wintering grounds.

You may also like:  Harlequin Duck (Histrionicus histrionicus)

Top Featured Image:
Gray-backed tern | image by Forest and Kim Star via Wikimedia Commons | CC BY 3.0 US