Seabird Surveys Across the Pacific with SPREP Scientists
Complementing NA166’s extensive seafloor mapping operations, this expedition includes topside surveys on the diversity and abundance of seabirds and other surface marine megafauna and activity in support of biodiversity surveys by the Secretariat of the Pacific Regional Environment Programme (SPREP). Gaining a better understanding of how seabirds, including migratory seabird species that use this open ocean pathway, will help all nations inform their conservation actions since oceans have no boundaries. Of approximately the 11,000 species of birds worldwide, only 370 are ‘seabirds’ that spend most of their lives at sea. Of those, 42 are known to breed within Oceania, with 17 unique to our region. Other species breeding outside the region will also pass through the areas that the expedition will cover.
Follow along with SPREP’s Threatened and Migratory Species Adviser Karen Baird and Chris Gaskin (Northern New Zealand Seabird Trust) in this ongoing blog!
4 October 2024: What do seabirds eat?
So, what do seabirds eat in an ocean that, at times, appears rather empty? There must be good food available to sustain the huge colonies of terns, noddies, boobies, and frigatebirds on a number of these atoll islands in Kiribati and the U.S. Pacific Remote Island Areas that straddle the equator.
That Wedge-tailed Shearwater hunts big fish? It's chasing the same prey that the fish are chasing. Tuna are near the top of the food chain in the open ocean: a predator of small and medium-sized fish that eats squid and crustaceans. Tuna, like many larger fish, force smaller prey close to the surface, where they feast, at the same time making that prey available to seabirds. These workups can make for spectacular feeding frenzies, and we saw a few of those as we approached Baker Island.
The other major prey item for many tropical seabirds are flying fish. Just think you have evolved an ability to fly to escape subsurface predators, like tuna, only to get picked off when you take to the wing. Dang!
5 October 2024: How do seabirds handle migration?
What a difference a day makes. We have been cruising these transects in the same general area for two days. We can see from the seabed mapping and the wonderful 3D modeling the submarine topography changes all the time. Topside, we were blown away by the sheer number of birds seen today, especially this morning. Short-tailed Shearwaters, like the Mottled Petrels that were such a feature yesterday, also like the colder climes and only transit through the tropics. This species breeds on offshore islands around Tasmania and the Bass Strait area of Australia and also ventures deep towards the South Polar Front when foraging.
We saw thousands of these birds pouring through in groups of up to fifty or more. They are also halfway on their journey back south, having pressed north, as far as the Bering Sea during their migration. In April, the year before last, we saw thousands of them heading north past New Caledonia, coming up through the Coral Sea after flying up the east coast of Australia. Free from breeding duties, they seemed ecstatic to be heading away for the southern winter.
These are birds made for speed - narrow wings, streamlined bodies, wee feet sticking out beyond their tails when they fly (a clue to their name). They are also extremely adept divers, able to dive 50m in search of prey such as krill, fish, and squid. Their beak is slender, with a hook at the end to assist in snatching their prey.
We are particularly interested in how well these migratory species fare when they spend these months on migration in the North Pacific. It is when they go through their annual molt, changing all their feathers progressively so they can continue foraging. It is also a period when they feed and get themselves in good body condition to meet the demands of parenting when they arrive back in Australia.
Sometimes, things can go wrong, such as the massive die-off of these shearwaters once they were back in Australia in 2023, an indication of something wrong in their Arctic foraging area that year. Let's hope they have fattened up nicely this year.
6 October 2024: When do seabirds sleep?
When do seabirds sleep? Well, the poop splatters on the Monkey and Forward Decks give a clue. We’ve had Red-footed and Masked Boobies hitching rides on the masts and upper superstructure some nights. Boobies, like a group of other seabirds (e.g., noddies, terns, tropicbirds, and some shearwaters), are visual feeders in the daytime. So, come night, they rest. If they are close to their colonies, they will return there and roost. However, over the open ocean, unless an obliging roost sails by (E/V Nautilus, for one), they sleep on the water. As seabirds, they are totally at home in the ocean.
Migrating shearwaters and petrels transiting through the tropics will also rest up. Especially when the wind speed drops. Flapping their wings is energy-sapping so they can wait out lulls until the wind picks up. Like yachts, they love a good breeze on which to sail.
That’s all fine if you can sit on the water, but there is one group of seabirds that cannot: Frigatebirds. There will be more on these birds later, but in terms of sleeping, and if you can’t chill out on the sea, what do you do? You sleep while flying! This study from the Galapagos shows that while sleeping mid-flight, frigatebirds don’t go completely on autopilot; the birds often sleep with only one side of their brain, leaving the other side awake.
8 October 2024: The eyesight of a Masked Booby
We often think of birds of prey like falcons and eagles as having exceptional eyesight. Boobies like this Masked Booby and their relatives, the gannets, have eyes that are angled forward and provide a wider field of binocular vision than in most other birds. They spy prey from a height, sometimes under the surface, and then plunge dive dramatically. On hitting the water, they are underwater for a short while, then bob up, with or without their prey.
However, seabirds’ vision is even more remarkable because they can see equally well above and below the water. While humans have to don a mask to create an air cell in front of our eyes, seabirds don’t need to. A study on gannets found that these birds can switch from well-focussed aerial to aquatic vision in less than 0.1 second — literally in the blink of an eye! These seabirds can change the shape of the lenses in their eyes. With the lens made more spherical when underwater, the light bends more, and a sharp image can be focused on the retina.
And it is not only boobies and gannets but other seabirds also, such as petrels and shearwaters, which are equally capable of making that shift. In Aotearoa, New Zealand, we ran a project examining petrels and shearwaters diving capabilities. What amazed us was their capability of seeing underwater.
9 October 2024: Bird Parasitism?!
There are many types of parasites, but out here on the ocean, we see a type of parasitism called Kleptoparasitism. This is really piracy, not parasitism, where one animal steals food from another. In the tropical ocean, frigatebirds rule. You will see them high up, often hanging above feeding groups of terns, boobies, noddies, and Wedge-tailed Shearwaters. They wait, watching, and when they spy a bird that has caught a fish, they will dive and pursue it with spectacular aerial acrobatics from both the hunter and the hunted. They will even tweak the other bird’s tail to force it to drop or regurgitate its prey, and if it does, it will swoop down and grab it often before it hits the ocean. True ocean pirates.
We’ve seen two species – the Great and Lesser Frigatebirds. And before you think too badly of these amazing creatures (remember they can sleep on the wing), most of the time, frigatebirds hunt their own seafood, flying fish as they skim the waves.
If there is ever a living bird that is closest to prehistoric pterodactyls, it would have to be frigatebirds. Like pterodactyls, they have huge wings, small bodies, and tiny legs and feet, ok for roosting and nesting in trees.
We have seen others from another group of aerial thieves on this expedition, the skuas. South Polar Skua (two) and a Pomarine Skua.
10 October 2024: Leach's Storm Petrel
We have seen flying fish every day and have discussed their being favourite prey for a number of seabirds in previous posts. But flying fish have to eat, so down the food chain we go. Flying fish feed on zooplankton and fish larvae. Not surprisingly there are a number of seabirds for whom zooplankton is their primary prey. This includes storm-petrels, the smallest seabirds we will encounter mid ocean. The smallest storm-petrel can weigh as little as 13g, the heaviest about 86g. In the context of the ocean these are really small birds, most will fit in the palm of your hand. But they are perfectly at home in the oceans, as their name implies, whatever the seas can throw at them.
We’ve only seen one species of storm-petrel on this expedition so far – Leach’s Storm-petrel. It breeds in the North Pacific, on islands off California all the way round to Hokkaido Japan and including some large colonies on the Aleutian Islands. They breed from April/May to September and then disperse, many heading south into the Central Pacific. The bird in the photograph is showing wear on the tips of its wing feathers, and it will soon undergo its moult, when it progressively replaces all its feathers before it returns to its colony to breed.
Storm-petrels belong to a group of seabirds known as ‘tubenoses’, which range in size from the really large albatrosses down to storm-petrels. Common to the group is that they have an amazing sense of smell, with storm-petrels the most acute. They use smell to detect potential food sources at sea and can do so from great distances. The name ‘tubenose’ comes from the arrangement of tube-like nostrils on their bills. To illustrate this here is a close up photo of storm-petrel we research back in Aotearoa New Zealand, the New Zealand Storm-petrel.
11 October 2024: The Sooty Tern
From 10nms adjacent to low-lying Baker Island, we could see the old beacon and the WW2 radio towers from a time when it was used as a refueling stop for US warplanes. It is nice to see land after five days of open ocean traveling from Pago Pago, American Samoa. But what was staggering was that at that short distance from the island, the sea below us was 5,000 meters deep. Such is the nature of many of these coral atolls and islands dotted across the tropical Pacific. Baker Island is a former atoll atop a seamount, one that pokes its head above the sea’s surface.
The island’s flat, desolate-looking surface is home to millions of seabirds. US Fish and Wildlife in 2007 recorded sooty terns (1.6 million), noddies, boobies, frigatebirds, and tropicbirds, and an earlier survey of the possibility of Wedge-tailed Shearwaters. After three days of open sea traveling, the numbers of seabirds encountered steadily increased, with frequent feeding and foraging aggregations of Sooty Terns, boobies, and attendant frigatebirds, while passing the adjacent Phoenix Islands and on our approach to Baker Island.
The rest of the science team aboard has been busy mapping seamounts north and west of Baker and Howland Islands. Seamounts are described as independent features of volcanic origin that rise at least 0.5 km above the seafloor, which, for the most part, in this region, is around -5000m. Those mapped are deep, with summits at around -3000m and -1000m. While it’s unclear how much influence these might have in terms of surface productivity, there is clearly sufficient to support the very large populations of seabirds on atolls and islands in this region. At home we have a great book in our library on seamounts.
12 October 2024: White Tern
Today, we saw quite a few foraging/feeding aggregations with White Terns, the dominant species, very strikingly bright white against sea, clouds, and clear sky. Sometimes with other terns, and Wedge-tailed and Tropical Shearwaters. This species really are truly pelagic in their foraging; the nearest land at midday was about 215nm east of Marakai Island, Kiribati, and we were 440nm west-northwest of Howland Island.
White terns construct no nest. Instead, it lays its single egg, often delicately balanced, on a branch, building, or rock. Newly hatched chicks have well-developed feet and claws with which they cling to their perilous nest sites. White terns haven’t been recorded on Howland and Baker Islands, but they have been recorded for several islands and atolls in Kiribati. In Hawai’i, White Terns are known as Manu-o-Kū, with a growing population within Honolulu, the busiest of Hawai’i’s urban landscapes. In Samoa, they are called Manusina and are a common sight flying inland over Apia, the capital city.
Another feature of the day has been the many smooth ocean surface slicks. These types of slicks have been well studied in coastal environments, for example, off Hawaii and California, where it is shown that they provide nursery habitat for diverse marine larvae. Whether that’s the case here in the open ocean, what we saw today with active fast-moving tuna schools, foraging and feeding flocks and terns, noddies, and shearwaters is certainly suggestive there is something out there!
13 October 2024: Red-footed Booby
Our day started off with entertainment plus. One of the two Red-footed Boobies that had hitched a ride overnight stayed on to give us a great display of ‘this is how to catch flying fish!’. After several miscues, he/she finally nailed it in spectacular style, much to the delight and shouts from the seabird team split between the fore and monkey decks. This bird was obviously good at pursuing flying fish, but it does beg the question of how young birds learn to catch their prey. A few days ago, we did see a pairing of an adult and juvenile Masked Boobies, with the adult taking the lead in most of the dives we saw. We know in Aotearoa, New Zealand, some terns are taught to catch prey by their parents.
But what of some of the migratory species – the petrels and shearwaters we’ve been seeing? Usually, the parents will cease visiting their single chick before it fledgests. So, when it comes to departing the colony, they will be well on their way to wherever their migratory path takes them. For those youngsters, they have never been to sea, the island and forest has been their home. But off they go. It’s tough that first year, and many don’t make it. But many do and return to their colonies, which is truly amazing.
Our route today took us north of the islands and atolls of Kiribati (the Gilbert Group) and south of the Marshall Islands, about 175nms between Mili Island (Marshalls) and Butaritari (Kiribati). Both groups run perpendicular to major current systems, the Equatorial Counter Current and the westward-flowing Equatorial Currents. Through the early afternoon we criss-crossed the boundaries between two of these currents; the water on one side smooth with few whitecaps, the other with a sea running as if we were crossing a shoal with wind-against-current kicking up a lot of whitecaps and standing waves. And not surprisingly, along this boundary was plenty of seabirds and fish school action, with numerous feeding aggregations.
14 October 2024: Bulwer’s Petrel
The modern distribution of seabirds across Oceania and the tropical Pacific is imperfectly known. There are numerous islands scattered throughout Oceania for which we know very little, or in some cases absolutely nothing, because of difficulty of access due to remoteness or natural barriers. Globally, seabirds are more threatened than any other comparable group of birds and their status has deteriorated faster over recent decades. In Oceania, the albatrosses, petrels, shearwaters, and storm-petrels (family Procellariidae - tubenoses), in particular, have lost more populations than any other bird family, mostly to predation from cats and rats.
Our bird of the day is Bulwer’s Petrel, a small all-dark petrel found in all three major oceans. It nests in crevices in rocks, in human-made or natural cavities, and even in the burrows of other birds. Mostly on small offshore or remote islands. We’ve seen a number this trip in the Baker/Howland/Phoenix area, but more commonly as we approached the Marshalls/Kiribati (Gilberts) and today as we press on towards the island of Kosrae in the Federated States of Micronesia (FSM). Today we have seen five. Some of the Bulwer’s Petrels would have been from the Phoenix Islands earlier in the trip. Others may have come down from Hawai’i (the largest colony is on Nihoa in the Hawaiian Chain) and/or Japan. Two of the birds clearly show moult, which generally follows breeding and may give us a clue as to which part of the Pacific they are coming from.
It is possible there are colonies of Bulwer’s Petrels yet to be discovered, and with eradication programmes recently completed or underway (e.g., Baker, Howland and Jarvis) this species and other petrels and shearwaters could recolonize them. Several species are known to occur in the Pacific and Oceania for which breeding sites are completely unknown and others for which breeding sites are suspected but not confirmed. Nothing like a challenge.
15 October 2024: Wedge-tailed Shearwater
If you have seen a large dark brown shearwater with a rather lazy flight moving across the waves and not appearing to be in any hurry, then it is undoubtedly a Wedge-tailed Shearwater.
It occurs in two plumage forms: dark-bellied and pale-bellied. They arewidely distributed throughout the tropical Pacific and Indian Oceans, where they breed on tropical and subtropical islands. Breeding is widespread on islands throughout the tropical Pacific, and as far north as the Hawaiian Islands and some offshore islands in Japan; south to the Kermadec Islands, New Zealand, and Lord Howe and Norfolk Islands, Australia. Breeding cycles are less strictly seasonal in equatorial birds than in birds at higher latitudes. We are likely seeing both trans-equatorial migrants as well as resident birds.
We are seeing Wedge-tailed Shearwaters most days. They have mostly been all-dark, with some a little smudgy around the face and underside, but not the full pale-bellied form so far. Shearwaters and petrels are not noted for beautiful calls. Wedge-tailed Shearwaters rarely call in flight, but regularly does so on ground or from within burrow, most frequently giving a
two-parted moan, likened to a child imitating a ghost, an "ooo-err". This call would definitely have resulted in fishers out around islands at night hearing ghosts or spirits.
SPREP is supporting work on this species in the Pacific. Wedge-tailed Shearwater chicks are harvested in remote communities in Vanuatu, and we are working with BirdLife International to support sustainable harvest regimes. Seabirds have been traditionally harvested across Oceania for thousands of years and in some countries, they remain an important cultural food source
and food security resource in difficult times such as when COVID hit. When communities had less access to outside resources. In addition, we are looking at plastics ingestion in this species and hope to establish a baseline for monitoring future changes in plastics ingestion and impacts.
Seafloor Mapping Offshore Howland and Baker Islands
Howland and Baker Islands lie just north of the equator, about 1,800 miles southwest of Hawaiʻi. The islands are low-lying, sandy coral islands ringed by narrow fringing reefs and surrounded by the deep ocean. The US exclusive economic zone around Howland and Baker represents one of the least explored regions under US jurisdiction.
