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).
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.
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| At dusk each day in the fall and winter the skies on Midway fill with thousands and thousands of Bonin Petrels. |
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.
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| 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.
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| 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.
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| 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.
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| 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. |
References
Fisher, H. I. and P. H. Baldwin. 1946. War and the birds of Midway Atoll. The Condor 48:3-15.
