The Moaning Birds

With less than six months to go here, I am feeling some urgency and want to be sure I have the chance to share with you more observations of the incredible wildlife of Midway Atoll. I've written quite a bit about albatross, touching on their fascinating courtship and breeding and also the precarious early lives of the chicks and their coming of age spectacle. In other posts I've written more broadly about the birds of Midway, the behavioral consequences of isolation and touched on some of the amazing marinecreatures whose lives reach onto the edges of the atoll.  But there is so much more!  So beginning with this post, my plan is to write a series of short pieces on Midway's wildlife so you can better appreciate the unique nature of this place.

While albatrosses and, in some locales, terns dominate during the daylight hours on Midway, once the sun sets, it is the petrels and shearwaters that rule.  Bonin Petrel and Wedge-Tailed Shearwater are nocturnal, burrow-nesting seabirds that have, since time immemorial, made their home on remote, uninhabited, oceanic islands where their nests are safe from rats, cats, dogs, snakes, and other predators. Like albatrosses, petrels and shearwaters are long-lived seabirds that spend most of their time in the open ocean returning to land only to breed. It is only there that I, a terrestrial organism, have the opportunity to observe them and so whatever information I am able to glean during these interactions is woefully incomplete. Their lifestyles also make them difficult subjects for scientific study so even today there is much that is simply not known about them.

"Bonin Petrel Season" begins in August when the birds make their way back to Midway from their maritime home in the Central Pacific Ocean to begin their long breeding season. Their frenzied courtship season lasts for nearly six months during which birds also attempt to establish a territory around their burrows. During this time, petrels – numbering in the hundreds of thousands - fill the sky every evening just as the sun begins to set. They fly high and low, circling, swirling in a way that reminds me of the huge "clouds" of Mexican free-tailed bats I used to watch during my summer at Carlsbad Caverns in New Mexico. Here on Midway, one of the only places in the world you can observe this, the phenomenon is known locally as a "birdnado" (bird X tornado).

At dusk each day in the fall and winter the skies on Midway
fill with thousands and thousands of Bonin Petrels.

Powerful and agile fliers, the petrels occasionally engage in high-speed chases. They seem pretty good at avoiding crashing into one another but not so much when it comes to "foreign moving objects" such as a human being out walking or, worse, riding a bike. This is both annoying and dangerous (for both human and petrel). Imagine getting hit in the face by a robin-sized bird flying at great speed as you pedal your way through the pitch black darkness on a pot-holed road! You can increase your chances of petrel-impact by wearing a headlamp. Often I've had to make the difficult choice of trying to navigate in nearly complete darkness without a light against the risk of getting "cold-cocked" by a petrel. 

After the sun goes down the petrels continue to fly, enabled by what must be excellent night vision.  Unlike bats, whose flights are mostly quiet, the Bonin petrel punctuates its flight with rather disturbing moaning, growling and screeching sounds. "Kukuer", "tititi" or "kikikiki", "kikooer", and "churr" are just a few of the ways these calls have been described though I'm not sure these really convey how un-melodic they sound. Better you listen to the sounds yourself by clicking on this link.

A pair of Bonin Petrels court near their burrow

As the night progresses, birds make their way to the ground covering the "lawns" and obstructing roads and walkways.  Birds may be solitary or be seen in pairs engaged in their various and courtship behaviors which include moaning, biting, preening and chasing. In addition to the birds, you may notice sand flying out of a hole in the ground. Petrels dig their burrows by picking at the soil with their bills and then kicking backward out of the burrow with their feet. Petrels are pretty open-minded about what is "habitat" and do not limit themselves strictly to the outdoors. I often encounter petrels in the garage at the office where the space between the chest freezer and the wall seems to be a popular "dating spot".  When I arrived last year, there was a freshly hatched petrel chick hidden behind a garbage can.

By morning the petrels have disappeared. Where did they go?  Some birds are probably out at sea while others remain in their burrows.  But even though the birds themselves aren't apparent, their numerous burrows, which seem like they might have been made by tiny badgers, make them impossible to ignore. Anywhere the sand is deep enough to allow it, a petrel has likely constructed its burrow and a large portion of Sand Island is perforated by them. Unlike a badger's burrow which you can typically walk over without collapsing it, petrel burrows are shallower and the sand and coral substrate makes them very unstable. Walking in an area with petrel burrows – that is, walking pretty much anywhere off an established road or trail – brings with it the high risk of falling into one. Like human-petrel collisions, this is also bad for both parties. People twist ankles and knees; eggs are crushed and birds become entrapped. Proper protocol after stepping into a burrow is to get down on your hands and knees to free any birds that were buried and to reconstruct the nest as best as possible. Walking across areas with petrel burrows is a learned-skill and someone who doesn't learn it well may be called, derisively, a "burrow crasher" (though not usually to the person's face). Obviously, a person's weight probably plays a role in whether or not they tend to fall into burrows so I wonder if this might too be a backhanded way of making fun of those, like me, that aren't exactly slender.

Once the nest is established and the single egg is laid things calm down a bit and the daily birdnado seems somewhat diminished. Like albatross, both male and female share in the incubation of the egg as well as the feeding of the chick. Nesting in a burrow apparently makes a lot of sense on a subtropical island as underground temperatures are cooler during the daytime and relatively warm at night. Predation of eggs and chicks by frigate birds and other aerial predators is also greatly reduced. Bonin Petrel chicks, round balls of gray and white fluff, begin hatching in March and they just might be the cutest thing you've ever seen. As they get bigger they learn to beg and one evening I was treated to the sight of a chick that had come outside its burrow being fed by its parent.  Like albatrosses, petrel parent feed their chicks by regurgitating stomach oil into the chick's bill.

A young Bonin Petrel chick

In late May petrel chicks begin to fledge though I will admit I'm not sure I've ever actually witnessed this as the fledglings look very similar to adults. After fledging, there is a brief period of time when Bonin Petrels are absent from Midway which provides a short window of opportunity for people on the atoll to get any projects done that require excavation or the movement of any heavy equipment off roads. Late summer and early fall is thus a very busy time for contractors here.

Though much less abundant than the Bonin Petrel, Wedge-tailed Shearwaters are hard to ignore during the times of year they are present here at Midway. The shearwaters don't seem to spend much time flying around over the island and, in fact, I hardly ever see them and have never seen one of their underground nests or a chick. Although I've read that they have a "musky odor", I will also admit to never having had the chance to verify this with my own nose.  So what could I possibly even write about?

The breeding season of Wedge-tailed shearwaters is distinct from that of the albatrosses and petrels beginning with first egg-laying in June and culminating in the fledging of chicks in November.  I wonder if this has something to do with the geographic range of the species which encompasses broad swaths of the Pacific and Indian Oceans both south and north of the equator (from Mexico to Japan and from New Zealand to South Africa!). As you might expect, breeding begins with courtship which takes place near the pair's burrow entrance and includes what might be the creepiest moaning sounds uttered by any bird. The sound, produced using their throat as well as a "gular pouch", is composed in two parts, a "OOO" made while inhaling and an "err" that is exhaled. You must hear it to truly appreciate it which you can do by clicking here.

A pair of Wedge-tailed Shearwaters

During this time of year, the sound of Wedge-tailed Shearwaters are heard nearly every evening. As these birds are not as numerous as petrels, the moaning is not ubiquitous, but rather emits from specific locations, often from within a stand of naupaka shrubs or ironwood trees. The localized, hidden sources of the sounds combined with the near pitch black darkness of the atoll, add to the eerie quality of the chorus. Here's how FC Hadden, a resident of Midway in the 1930s, described it:

Any person taking a walk around Midway in the evening when it begins to get dark, during March or April, is apt to have a most hair-raising experience. Suddenly out of the dark will rise the most blood-curdling howls, yowls, moans, and groans. Not only that, but it sounds as if there must be a dozen tomcats tearing each other to pieces, from the wild cat-like shrieks that penetrate the ear, then some woman begins to groan and gasp and moan, as though about to die in the greatest of pair. All of these various ghoulish noises are so heart rending, so horrible, that one must indeed be brace to investigate them. What a horrible experience it must have been for those first sailors who were shipwrecked here many years ago. Certainly they huddled around their fire trembling and shaking when they first heard these wild cries. 

Early residents of Midway referred to the Bonin Petrel as the "small moaning bird" and the Wedge-tailed Shearwater as the "large moaning bird".  Unlike the albatrosses, whose daytime habits, humorous antics and outgoing personalities endeared them to people, the "moaning birds" were mostly scorned. Being creatures of the night, one can only imagine that some thought of them as evil. This was after all one hundred years ago when people were less scientifically-minded and more superstitious (although these days I often wonder how far we've actually come). The burrows that they made were also an inconvenience, not just because they made walking difficult but they also reduced harvests from the gardens that were established to provide food for the island's residents (today, there is an enclosed greenhouse). During the Navy years the petrels and shearwaters continued to be treated badly.  Ornithologists Harvey Fisher and Paul Baldwin visited Midway in 1945 to investigate conditions for the various birds there and reported

The "moaning birds," of which the Wedge-tailed Shearwater was the most dismal-voiced, were generally disliked by the men. They received little sympathy, burrows were purposely tramped down and adults were persecuted constantly. This was the only openly discussed form of deliberate destruction of birds we found, as irresponsible target shooting was done more or less on the sly and was not generally approved. Bonin Island Petrels were in areas desired for lawns and consequently were destroyed. Bulldozing in certain areas must have killed thousands of shearwaters and petrels in their burrows.

Although data are scant, the numbers of petrels and shearwaters are thought to have declined precipitously on Midway throughout the years when the Navy maintained its air station. In addition to direct persecution and destruction of habitat rats,which were transported to Midway by ship sometime in the early 1940s, also took a heavy toll. By the time that the US Fish and Wildlife Service took over management of the atoll in 1996, populations of these birds were at just a fraction of their original numbers.

Today, Bonin Petrel populations appear to have rebounded to approximately their original numbers – the best guess is somewhere around 1 million birds, although large areas of the atoll, especially Eastern Island are still covered in pavement and thus inaccessible to them. As this is a species with a relatively small geographic range, this recovery holds real significance for the global population (its other strongholds are volcanic islands off the coast of Japan). For reasons that are not clear, Wedge-tailed shearwaters have been slower to recover, perhaps a consequence of their more restrictive habitat requirements. Habitat restoration efforts aimed at increasing the amount of sand dune and naupaka shrub habitat may aid in their recovery.

Nocturnal, burrow-nesting birds are in need of good PR. Special events
can help educate the public as to the great value of these birds.

 As an agency committed to the conservation of birds and other wildlife, the US Fish and Wildlife Service has taken exceptional measures on Midway to ensure that petrels and shearwaters will continue to thrive at Midway Atoll. One thing that hasn't changed though is the difficulty that people seem to have in liking these birds. Some seeking to change public opinion have created small informational placards that sit next to the salt and pepper on the tables of the Clipper House. Others have gone as far as putting on special events in their honor, for example, the Bonin Petrel Appreciation Night that was hosted last January by visiting seabird biologist Roberta Swift. Maybe the PR is working. After a year, I can honestly say that after some hesitation I have become a genuine fan of the "moaning birds" and look forward to proudly displaying a portrait of a Bonin Petrel on the wall of my living room back in Oregon when my time here is through.


References



Fisher, H. I. and P. H. Baldwin. 1946. War and the birds of Midway Atoll. The Condor 48:3-15.

Hadden, F. 1941. Midway Islands. The Hawaiian Planters Record 45:179-221.