The Black-bellied Storm-Petrel (Fregetta tropica) is a small seabird in the storm-petrel family that breeds on islands in the southern Pacific. It is a unique and fascinating species that is often overlooked due to its elusive nature.
In this article, we will take a closer look at the identification, plumages, and molts of the Black-bellied Storm-Petrel.
Identification
Field
Identification: The Black-bellied Storm-Petrel is a small, dark seabird with a distinct white rump. It has long and narrow wings, a slightly forked tail, and a short, black bill.
In flight, it appears as a rapid and agile flier that skims the surface of the water. Similar Species: The Black-bellied Storm-Petrel can be easily mistaken for other storm-petrel species due to their similar size and appearance.
It is most commonly confused with the Wilson’s Storm-Petrel. However, the Black-bellied Storm-Petrel has a distinctive white rump, while Wilson’s does not.
Other storm-petrels such as the Leach’s and Band-rumped have longer bills that are more hooked and distinguish them from the Black-bellied.
Plumages
The Black-bellied Storm-Petrel has two distinct plumages, the breeding, and the non-breeding. During the breeding season, adults display a blackish-brown plumage with a contrasting white rump.
The underparts of the bird are black, with the black extending up to the chin. Adult’s faces have a delicate white crescent arc behind and around the eye.
The bill is black and stubby. The eyes are dark brown and have a circled evenly with white eyelids.
Feet are small, with webbed toes and varying colors of grey, pink and blackish. The non-breeding plumage is similar to the breeding plumage; however, it is paler overall, with less contrast between the white rump and the rest of the plumage.
Molts
Like all seabirds, the Black-bellied Storm-Petrel goes through different molts as they age. The sequence of molts in petrels is different from most birds in that they replace old feathers slowly throughout the year, rather than going through a discrete period of molt.
Juvenile plumage resembles the non-breeding plumage but slightly lighter with chestnut undertail coverts that contrast with Pale body. Adult plumage starts to grow on the juveniles feeding patch on their face around the eyes.
From this point, adult feathers slowly replace juveniles over the first two years, as the bird remained in the nest, immobile, and fed by their parents. It reaches full adult plumage at around five years old.
In conclusion, the Black-bellied Storm-Petrel is a unique and fascinating bird species that warrant more attention and appreciation for their remarkable and elusive nature. Although they may be challenging to identify due to their similarity to other species, their distinctive white rump can make them stand out if observed carefully.
Understanding their plumages and molting cycles can help with accurate identification and a deeper appreciation of the Black-bellied Storm-Petrel. Systematics History:
The Black-bellied Storm-Petrel is part of the family Oceanitidae, which comprises only around five species of small seabirds.
The first descriptions of the Black-bellied Storm-Petrel were made by the famous French naturalist Louis Jean Pierre Vieillot in 1818. He named the bird Thalassidroma fuliginosa, which remained the species’ official name until it was changed to Fregetta tropica in 1972.
Geographic Variation:
The Black-bellied Storm-Petrel has a vast, continuous range across the Southern Hemisphere. They breed on islands in the South Pacific Ocean, from Easter Island in the east to the Falkland Islands in the west, and from New Zealand to the Galapagos in the north and south respectively.
They are highly pelagic birds, often found far from the nearest landmass, feeding exclusively at sea.
Subspecies:
The Black-bellied Storm-Petrel has no distinct subspecies.
There have been some suggestions of geographic variation, with birds from the eastern Pacific suggesting slight differences in morphometrics and vocalizations. Nevertheless, genetic research supports taxonomic homogeneity throughout the species.
Related Species:
The Black-bellied Storm-Petrel has two closely related species, the White-bellied Storm-Petrel (Fregetta grallaria) and the Polynesian Storm-Petrel (Nesofregetta fuliginosa). The White-bellied Storm-Petrel and the Black-bellied Storm-Petrel are very similar in appearance, with the White-bellied exhibiting a white belly and undertail coverts.
The Polynesian Storm-Petrel is a slightly larger bird, with dark plumage, and an occurrence restricted to the Pacific Islands. More molecular studies are still necessary to fully understand the relationships between these three taxa, but it seems likely that the two Fregetta species are more closely related to each other than to Nesofregetta.
Historical Changes to Distribution:
Throughout the late 1800s and early 1900s, human activity such as guano extraction and colonization of islands had little impact on the Black-bellied Storm-Petrels populations. However, in the mid-1900s, large-scale changes began to take hold.
In 1955, the British Royal Air Force established a base on the Falkland Islands, leading to a significant anthropogenic influence on the birds habitat. The only known breeding colony in the Falklands was declimated when petrels fled to sea as operations began on building the RAF Base in the vicinity.
Similarly, the French began withdrawing its colonization in the South Pacific in the late 20th century. The subsequent abandonment of the Kerguelen Islands resulted in the loss of the world’s largest known colony of Black-bellied Storm-Petrels.
As well, the closer proximity of populations with the rest of the world increased the risks of the species contracting introduced diseases, leading to serious population declines in some regions. Additionally, the illegal practice of harvesting chicks and eggs so prevalent throughout the past significant part of the 20th century may have contributed to population declines which still persist to some extent today.
More recent studies suggest that the Black-bellied Storm-Petrel populations have not decreased as much as once thought, with the global population estimated at around 3 million individuals. Still, the species is listed as Near Threatened under the IUCN Red List due to threats facing various colonies such as invasive species, the potential danger of oil spills, and random bycatch in longline fisheries.
In conclusion, The Black-bellied storm petrel is a fascinating species with a rich history and important ecological role. Although it is a seabird that is often difficult to study, it has a complex geographical distribution and faces human-induced threats that may impact its survival beyond its current near-threatened status.
It is essential for researchers, management authorities, and the general public to recognize the importance of these conservation efforts and try to ensure the continued survival of this species. Habitat:
The Black-bellied Storm-Petrel is a marine bird with a wide distribution in the southern Pacific.
They are a pelagic species, mainly inhabiting the open ocean and the inter-tropical convergence zone. These regions are characterized by an abundance of marine organisms, including small fish, squid, and plankton, which provide the primary food source for storm-petrels.
Black-bellied Storm-Petrels breed on remote, predator-free islands, often in burrows in areas where lush vegetation and caves, cliff-side crevices, or rocky slopes provide protection. They typically choose islands that have somewhat flat surfaces and patches of short vegetation.
They would regularly venture away from the nesting spots come the evening to feed.
Movements and Migration:
Black-bellied Storm-Petrels are highly-mobile, and their movements and migration patterns are still largely unknown.
They undertake long-distance foraging trips, covering large distances in search of prey. To date, their migration patterns are not well understood, but it is thought that they follow a circular route, with birds from the Pacific traveling east across the South Pacific to breed in the Atlantic on Tristan da Cunha and Gough Island in the South Atlantic.
While their migratory patterns are not well-documented, the Black-bellied Storm-Petrel has been found far from its breeding grounds on occasion. There have been recorded observations of individuals traveling nearly 4000 km away from breeding colonies, as seen ringed individuals recovered on the periphery of the Indian Ocean and as far East as the Pacific Coasts of Central America.
Several of the species’ colonies are at risk of decline due to changing oceanographic conditions. With overfishing and climate change altering the distribution and abundance of suitable prey such as krill, some colonies are locations foraging males may have to travel greater distances outside of known breeding habitats to find adequate food.
This challenge is a major threat to the species’ survival, more so for those colonies located in areas where humans have occupied. Oil spills and industrial fishing activities also pose threats, causing illness or death of birds.
In 2011, a catastrophic petroleum spill occurred in the Guafo Island region of Chile, which caused thousands of seabird deaths and ecological consequences that persist today. In conclusion, the movements and migration patterns of the Black-bellied Storm-Petrel are still not fully known.
Like most pelagic birds, they have broad habitat ranges and regularly traverse vast expanses of ocean in search of prey. Changes in food availability and environmental challenges threaten this species, placing them in a perilous state.
As such, more research is needed to gain a better understanding of their movements and habitat needs to effectively protect and conserve this fascinating and elusive species. Diet and Foraging:
The Black-bellied Storm-Petrel is a marine bird that feeds entirely at sea.
It is highly specialized, feeding primarily on small fish, squid, and other pelagic organisms, which they catch by fluttering above the water’s surface or diving into the water. Unlike other storm-petrels, it is not known to follow ships, and its foraging locations are difficult to study due to their remote and pelagic habitat.
Feeding:
Black-bellied Storm-Petrels have a unique feeding behavior. They mostly feed at twilight, skimming the surface of the water or diving underneath the surface to hunt.
When feeding on the wing, they flutter rapidly, with a wingbeat rate of up to 70 beats per second, hovering just above the water’s surface. By doing this, they disturb the water’s surface, causing small prey items to jump into the air, where they are caught by the birds.
When diving, Black-bellied Storm-Petrels can reach a maximum depth of 20 meters. Diet:
The diet of the Black-bellied Storm-Petrel is primarily made up of small fish, squid, and marine invertebrates.
They are known to feed on mesopelagic organisms such as lanternfish, myctophids, and invertebrates such as krill during some specific times. Studies of the stomach contents of Black-bellied Storm-Petrels have found small amounts of plastic particles, a worldwide issue of concern affecting oceanic birds.
Metabolism and Temperature regulation:
Black-bellied Storm-Petrels have a unique physiology that allows them to forage at sea for extended periods of time without returning to land. These adaptations include a low metabolic rate and the ability to regulate their body temperature.
Like other seabirds, Black-bellied Storm-Petrels have an enormous respiratory system and can store air in their bones, which allows them to maintain buoyancy in the water.
Sounds and Vocal Behavior:
Black-bellied Storm-Petrels are vocal birds and are often heard calling in flight.
Their vocalizations are typically high-pitched, rasping, and nasal. The call of Black-bellied Storm-Petrels is a sequence of screeching or throaty calls, typically heard during the breeding season (May to September).
A later discovery of a new type of Black-bellied Storm-petrel on the Pacific Islands that is genetically related to the Atlantic Black-bellied but has a different body structure and distinctive vocalizations exposes how little is known about these birds in general.
Vocalization:
The Black-bellied Storm-Petrel’s vocalizations provide important clues about their behavior and could assist in locating colonies on remote islands.
Both males and females vocalize, especially during aggression or communication of shared space over colonies. Male Black-bellied Storm-Petrels tend to be more vocal than females during the courtship and breeding process, and they produce a range of calls to attract a mate.
The calls evolve over time, and specific calls are endemic to some colonies.
In conclusion, Black-bellied Storm-Petrels are fascinating birds that adapt to a unique lifestyle in a remote and pelagic habitat.
As they feed exclusively at sea, they have developed specialized feeding techniques and diet preferences. Understanding their foraging behaviors and vocalizations will provide a better knowledge of their ecology and how to conserve this elusive seabird.
Ensuring the preservation of their preferred habitats is imperative for the protection of the Black-bellied Storm-Petrel. Behavior:
Black-bellied Storm-Petrels exhibit various types of behavior, including locomotion, self-maintenance, agonistic behavior, and sexual behavior.
Locomotion: Black-bellied Storm-Petrels are fast and agile fliers, with a wingbeat rate of up to 70 beats per second. They usually fly close to the water’s surface, often skimming or touching it with their wings.
Dependably, they can be observed performing butterfly-like, intermittent, and noisy flights to capture prey easily.
Self-Maintenance: Black-bellied Storm-Petrels are solitary birds, but they can be observed in a mixed-species flock, feeding and flying together during the non-breeding season.
During self-maintenance, the birds preen and shake their feathers to maintain their plumage. Agonistic Behavior: Black-bellied Storm-Petrels exhibit agonistic behavior towards other seabirds who try to encroach on their nest area or potential feeding zones, this behaviour increases during the breeding season.
Sexual Behavior: During the breeding season, Black-bellied Storm-Petrels exhibit distinctive sexual behavior. Mating systems show genetic monogamy, which means partners tend to stay loyal to one another and protect their burrow.
Breeding:
Black-bellied Storm-Petrels forms burrows in grassy or mossy habitats where breeding occurs, or less frequently above ground between boulders or rock crevices. The birds generally lay only one white egg per breeding season, which both male and female birds take turns incubating for a period of 39-41 days, from November to January in the Southern hemisphere.
Once hatchlings are born, feeding remains solely on the parents until they fledge, approximately 45 days after hatching. Black-bellied Storm-Petrels are year-round species, though they tend to breed in large numbers during the austral winter, taking advantage of the relative warmth and light in higher latitudes.
Demography and Populations:
The Black-bellied Storm-Petrel is a relatively common seabird species, with a population estimated globally at approximately 3 million. The vast majority of these birds are found in the South Pacific, though smaller populations occur in areas such as the Falkland and Galapagos Islands.
One of the reasons for their relatively stable populations despite ongoing threats may be a holistic view of well-planned breeding colonies management and peaceful co-existence between them and humans.
While Black-bellied Storm-Petrels appear to be a species that manages to maintain stable populations over time, several smaller breeding grounds are vulnerable due to emerging threats from various sources.
Grazing pressure from introduced herbivores and erosion of nesting areas by anthropogenic activities like land restoration is also a direct influence on the reproductive success to breeding pairs.
To ensure the Black-bellied Storm-Petrel population remains stable, proper habitat protection measures must be implemented with focus on sustained anthropogenic welfare.
Fortunately, breeding populations are found on isolated but uninhabited offshore islands, indicating the importance of the protection and conservation of these sites. In conclusion, while Black-bellied Storm-Petrels are highly specialized seabirds, their behavior patterns share similarities with those of other seabird species who spend significant time in their offshore environment.
Proper attention to habitat protection and anthropogenic welfare is critical to ensure the survival of the species. Through collaborative efforts by researchers, management authorities, and the public, effective conservation strategies can be adopted to protect Black-bellied Storm-Petrels from future threats.
The Black-bellied Storm-Petrel is an elusive and fascinating seabird that is found throughout the Southern Hemisphere. This small bird possesses unique physiological adaptations, a distinctive vocalization repertoire, and displays fascinating behavior patterns during the breeding season.
While it seems the global population is relatively stable, isolated threats, such as invasive species and industrialization activities, have emerged, jeopardizing specific colonies. Understanding of these threats, their ecology, movements, and habitat needs,