Friday, December 1, 2017

For Lost Species Day, two species hanging on.

Yesterday was @LostSpeciesDay, which I didn't learn until late in the evening.  (Where is the official list of @days?)  I can, and do, mourn lost species, but I wanted to add a splash of hope, point out two extremely endangered species that are hanging on, perhaps are even on the way back, thanks in large part to the hard work of dedicated conservation biologists.

This is a story of the Bermuda Rock Lizard, which is a kind of skink, and the Cahow, a seabird.  It is a gadfly petrel, a group of about 35 species that nest on oceanic islands.  It is considered the second-rarest seabird in the world.

Image result for cahow



I met both in the 1990s when I was a graduate student at the University of Toronto. I was studying the skink genus Plestiodon, which was then still part of the bloated catch-all genus Eumeces.  Skinks, I'm sure you know, are mostly small- to medium-sized, slender, ground-dwelling lizards with shiny scales.  Many species have reduced or absent limbs.  I was using various techniques to break up Eumeces into smaller, related groups that would better reflect the evolutionary relationships among species.  Plestiodon, which contains most of the North American and East Asian species of what was once Eumeces was pretty clearly an independent evolutionary entity, hence the renaming.  One species that didn't quite fit though, was the Bermuda Rock Lizard, or Bermuda Skink, which shared the colour patterns, juvenile and adult, of its continental counterparts, but lacked several derived, defining features, particularly the pronounced sexual dimorphism between males and females. In continental and east Asian species, the males had broad skulls and powerful jaw musculature, presumed to be related to bloody territorial battles that decide breeding rights.

Bermuda Skinks are different.  The males and females are, externally, almost indistinguishable.  I discovered this among the towering shelves of pickled specimens in the herpetology collection at the National Museum of Natural History in Washington.  I was examining individuals from as many species as were available in the collection, and was puzzled by the specimens of what was then called Eumeces longirostris, the Bermuda Skink.  I fanned out the lizards on a plastic tray.  You pretty much had to take a scalpel and peek inside, take a look at the gonads, to determine boy or girl.  There were other differences from the continental species too, particularly in the shape of the head.  Mainlanders had a typical skink head, flattened back to front and with a rounded nose, but the Bermudians had a gently tapered muzzle, like a Shetland sheepdog.  Bigger eyes too. 

I noticed that the Bermuda Skinks had been collected by the curatorial assistant in the NMNH Herpetology Department, the fellow who had helped me get set up in the collection.  I went to his office and asked him questions about the habits of the skinks in Bermuda.  Why didn't the males have expanded heads?  Didn't they fight?  He didn't know.  His visit to Bermuda had been brief, and he hadn't done much with the skinks apart from collecting them.  Ever helpful though, as curatorial assistants are, he gave me the name and address of a biologist in Bermuda.  "Ask him," he said.

So I wrote to Bermuda, to Dr. David Wingate, whom I had no knowledge of.

I got a letter back.  David, aside from being Bermuda's Conservation Officer, was an ornithologist, not a herpetologist, but was concerned about the skinks.  Their numbers on islands where they had previously been plentiful had diminished greatly.  I was welcome to come and try to figure out why.

It's only slightly better than a 2 hour flight from Toronto to Bermuda, which is the world's northernmost coral atoll.  The gulf stream keeps it warm, and its proximity to eastern North Armerica has influenced its flora and fauna, resulting in a mix of Carolinian and Caribbean.  There is only one extant native terrestrial vertebrate, the Bermuda Skink, known locally as the Bermuda Rock Lizard.

However, rather than being related closely to eastern North American species, the Bermuda Skink is a remnant of a more distantly-related line, now lost from that region, which may explain its differences in form and behaviour. I suspected this at the time, but had no means of testing it.  Since then, molecular studies have shown this to be the case (e.g., Brandley et al., 2010), that Bermuda has served as "an evolutionary life raft" for an ancient American, otherwise extinct, lineage. 

Off I went.


Hellooooo Bermuda Rock Lizards!

I became aware of Cahows not long after the plane landed. David Wingate met me at the airport.  He had told me over the phone to look for a grey-haired man with binoculars around his neck.  He wasn't hard to pick out.  As one person had told me, "He looks like Zeus."

From the airport we drove in a small pickup truck across the long and narrow causeway, along winding roads through golf courses, to a small concrete wharf, where we loaded my luggage into a Boston Whaler and headed off across Castle Harbour toward Nonsuch Island, which would be my home for the next six weeks.  

However, en route David asked if I wouldn't mind if he took a slight detour to check on a Cahow nest.

Cahow?

We crossed the harbour, which is bounded on one side by the airport, the other by a long peninsula and a scattering of smaller islands, the largest of which is Nonsuch, and continued into open water.  The water in the harbour had been a bit rough.  Outside was worse.  The boat yawed and pitched as David aimed at an almost barren, ragged rock.  He cut the engine near the rock, which was going up and down relative to us, and tossed an anchor over the back.   The chain clattered out.  Then, as we we drifted near, going up and down and also left and right, one of us feeling nauseous and about to lose his airplane lunch, David plucked up a rope and leapt from the boat, landing like Bugs Bunny escaping the plummeting plane, jumping up at the right moment and landing softly.  He used the rope to pull the boat closer.  I was supposed to jump out next.

I had expected Bermuda to be like the Florida Keys, sandy-smooth and flat as a pancake.  It wasn't.  It was grey knife-edges and petrified meringue pointing in all directions, interspersed with deadly gaps.


I took this picture later that day, a view from Nonsuch Island.

Somehow, eventually,  I managed to leap across and not die, and then, afterward, successfully return to the boat.  Some traumas get blotted out.  I later learned that the sea had been unusually rough that day, the remnants of a tropical storm.  

I also learned that Cahows were seabirds endemic to Bermuda that for more than 300 years had been believed to be extinct.  They were rediscovered when David was a teenager in the 1950s.  He had been part of the group responsible for their rediscovery.  At this time of year the adults were out at sea during daylight and would return after dark to feed their single chick, which was in a burrow deep in the rocks on one of the few islets in Bermuda that had not been overrun by humans and their associates (dogs, cats, rats).  At the nest, David had used a mirror on a pole to look deep into the burrow and around a corner to see how the chick was coming along.

Apparently he did this almost every day.  He knew the location of every Cahow nest in Bermuda and checked them all regularly, no matter how precarious their location.  He had been doing this for years, charting the breeding success of the species, enhancing their habitat, keeping rats and other predators at bay. 


David Wingate in the Whaler


For the next several weeks I trapped, measured and charted the distribution of skinks on Nonsuch Island.  


Measuring snout-vent length of a Bermuda Skink.

I discovered that very few were surviving the first few years, that the population consisted mostly of elderly lizards.  Something(s) was killing the young.  It was likely that introduced birds (Kiskadees) were a major culprit, but we later discovered that introduced Jamaican Anoles (another kind of lizard) also preyed on the hatchling skinks, and it seemed likely that the once extirpated, re-introduced Yellow-crowned Night-herons were also preying on skinks, including adults.

From daily conversations with David I learned a lot about Cahows.  Toward the end of my stay he was going out at night in the near pitch black to watch the fledgling birds emerge from the burrows and test their wings.  Once the chicks develop to a certain stage, the parents stop returning to feed them.  The young birds must leave their burrows on their own, or starve.  They do this progressively over a series of nights.  The youngsters emerge, walk around a bit and flap their wings.  Sometimes they find a rock or other higher feature on which to flap.  A nearby human sitting motionless will suffice.



One night several of us went along with David to watch a fledgling emerge on Horn Rock, which is the low-domed island in the top-center of the above image.  We pulled alongside in the dark, and by this time I was relatively competent in getting in and out of the Whaler at random, rocky spots.  We sat on mattresses that had been placed near the burrow and had been there for at least one good rain storm, and waited, silently, damply, listening to the sloshing of waves along the chaotic shore Eventually the bird appeared.  It was pigeon-sized, but with a relatively large head and a narrow, hooked bill.  It walked among us silently.  It had a fishy, oily odor.  It paused to flap its long, pointed wings.  It walked some more, and, if I am remembering correctly, climbed on the lap of someone and repeated its flapping routine from atop his knee, working to strengthen its flight muscles.  We remained silent, motionless and mesmerized, as if watching a sleepwalker, afraid to wake it, or a ghost.  It returned to its burrow, done for the night.  One of these nights it would take wing and fly out to sea, not to return until ready to breed in three to six years.

When I was in Bermuda, there were 40 to 45 breeding pairs of Cahows, which were all on the smaller, difficult as heck to visit islands. In recent years, Cahows have been encouraged to breed on much larger and more accessible Nonsuch Island, thanks to daring transfers of chicks to artificial burrows on that island, made necessary by damage to traditional nests on smaller islands during a series of hurricanes in the early 2000s. The first artificial burrows were made of concrete, and were back-breaking to create. Later, prefabricated plastic burrows--carefully shaped, plastic tunnels buried in the soil with a lid above the nest chamber that could be opened to examine both adults and chicks--were developed. Although he retired in 2000, David Wingate was instrumental in getting the burrows custom-designed for Cahows, and built. The person presently in charge of Cahow conservation, having taken over after David, is Jeremy Madeiros, who is about my age and was a recently-hired conservation officer when I first visited. We became good friends over the four summers I stayed on Nonsuch Island to study the skinks.

The 2016-2017 breeding season resulted in 117 breeding pairs of Cahows, producing a record total of 61 successfully fledged chicks. A complete account of the history of the bird's ongoing recovery, including a link to a live nest cam, is here. My old friend Jeremy is featured too. He is now Bermuda's Senior Terrestrial Conservation Officer.

To bring this full circle: The Cahow nest cam caught a Bermuda Skink checking out a Cahow nest. It is believed that prior to the arrival of humans on Bermuda, when the islands were thick with nesting seabirds, the skinks wandered from nest to nest, gobbling up whatever messy bits lay about (seabirds aren't particularly tidy.) The species had evolved to live together, one the food source, the other the waste removal engineer. Notice the skink flicking its tongue. They have a highly developed olfactory sense, which they use to find food. I caught them by baiting half-buried 1-litre pop bottles with sardines. Unfortunately, their sense of smell and love of stink also causes them to follow the scent of stale beer into discarded bottles, where they tend to perish before finding their way back out.




Skink in a pop bottle trap, next to a hunk of sardine.

Since my time on Nonsuch, others have continued studying populations of Bermuda Skinks on Nonsuch Island and in other localities, and have made advances in understanding their population genetics and life history. Some captive breeding has been carried out.

For both Bermuda Skinks and Cahows the future is looking a little brighter.

It was a real treat, on @LostSpeciesDay to come across the following video, a healthy adult skink in an active cahow nest (pre-egg, adults out feeding or courting).



4 comments:

Tim said...

It's an amazing thing, our technology. It not only lets us observe behaviours that 20 years ago could not be imagined, but let's us share it with the world.

Sally said...

Great, fascinating post. Among other things, I guess I thought [all] reptiles ate "meat," that is, live food, not scavenged. Thanks for the wonderful complement to the Tea Kettle stories!

Hugh Griffith said...

Sally, Sorry I didn't see your comment until now. Thank you.

The Bermuda skinks eat almost anything, which has contributed to their dire state.

Hugh Griffith said...

Tim, yes, a really good use for it, for a change.

I had to lie on my belly in an ant-infested forest to watch these little guys. I wouldn't trade that for anything though.