Great Shearwaters are Unusual Guests on our Beaches

It all started with an injured bird.  I got a report of a gull-like bird that had flown in and basically collapsed on the beach. Claudia and Richard sent a photo so we could figure out where to send the bird. But wait~ this bird didn’t look like a gull!  I had to do a little googling and enlist the help of the Merlin app.  This was a great shearwater, and we have never recorded a live sighting on the island before! We called the Avian Conservation Center to arrange to get the bird to them for evaluation.  By the next morning, reports were surfacing about stranded and dead shearwaters all along the Southeast Coast. I had so many questions: I’ve seen these birds wash up before, but never alive.  And I wanted to learn more about what healthy birds are like.  And thus began a rabbit hole of research and being constantly amazed by the generosity and curiousity of scientists, people who work with wildlife, and volunteers.

great shearwater

Making New Friends While Talking about Birds

In order to understand why we were seeing so many on the beach, I wanted to understand what the life cycle was like for these pelagic (oceangoing) wanderers. So I reached out to a few traveling birders, and my sister-in-law Virginia sent me to the Facebook page for a sea-birding guide named Kate Sutherland.  Besides having several friends in common, Kate and I connected over her enthusiasm about “tubenoses” in general and Great Shearwaters, AND she provided lots of video footage and photos of birds in flight. (If you ever want to go see these birds, you can book a pelagic trip out of Hatteras, NC! Kate has been keeping sea bird records for 23 years for SeaBirding. You have Kate to thank for most of the photos and footage in the following video:

Great Shearwaters are Epic Migrants

More Fascinating Facts about Shearwaters

They are one of the few migratory species near us that nest in the Southern Hemisphere and fly north for food.  (For example, our Whimbrels come through on their way to the arctic circle to breed, as do many of our shorebirds like black-bellied plovers, sanderlings, dowitchers, dunlin, etc.). They can dive deep for prey and swim underwater, flapping their wings like penguins.  They navigate the world by scentscape the way others use landscape. They can desalinate their own water.  They spend most of their lives over the ocean, so normally birders have to get in a boat to see them. They breed in only a few remote places, with millions of birds nesting in burrows in the ground on a few volcanic islands in the middle of the Southern Atlantic Ocean 1500 miles west of Capetown.

image ©Kate Sutherland
image ©Kate Sutherland
image ©Kate Sutherland
image ©Kate Sutherland

A Big Mortality Event?

It became clear that we were just seeing the beginning of some type of mortality event.  There’s been a lot of concern about Avian Flu~ could that be the issue?  What about all the sargassum washing up on the beach?  Is that connected?  Is it a cause?  Isle of Palms reported several dead birds and a few live ones.  We found a few more on our beach.  Since someone from each turtle team along the coast walks the beach every day, we began hearing about them on Edisto, Folly, IOP, and Cape Islands.  North Carolina beaches also reported. Mary Pringle on the Isle of Palms worked with the police and volunteers there to understand what might be going on.

image ©Nancy Willms
image ©Nancy Willms
image ©Nancy Willms

Our Local Experts and the Literature Point to this Being Part of a Normal Cycle

I also checked in with Craig Watson, our USFW helper with creating shorebird habitat, and he recommended this paper, which looked at unusual shearwater mortality events in the Southeast.  SCDNR sent some carcasses off for testing, but those results will probably take time.  We do know that none of those birds turned up positive for Avian Influenza. The bird we sent to the Avian Conservation center did not survive, but Valerie Sprinkel, a medical technician there,  shared some more scientific literature with me: This paper on Shearwater Mortality from spring 2009, and this look at future conservation concerns of petrel species.

Basically the literature ALL points to this being a normal situation made more obvious by the recent onshore winds~ the same winds that drove Sargassum ashore in big drifts.

And the link between the two is probably not one of causation, but one of commonality~ those onshore winds brought both ashore.

Because they are open ocean foragers, not much is known about the normal mortality of young birds.  Not all hatchlings of every species would be expected to survive, particularly along such an arduous journey.  When strong onshore winds push the sargassum ashore, birds that may have otherwise perished over the open ocean and become part of the food chain ended up being much more visible to beach-goers on the East Coast.

Looking at Strandings for Information

Valerie Sprinkel, at the Avian Conservation Center, answered some of my questions about the other stranded Great Shearwaters at the center.  Valerie is a bird rehabilitator, not a scientist, but, like me, she is curious to learn about whatever contributing factors might exist that would result in a big die-off.

None of the 22 stranded birds that were sent to the center survived. Some were dead on arrival, some died shortly after arrival, but none survived.  Since the focus of the staff there is to try to help the injured and sick birds, there’s not a lot of time for necropsies, but Valerie had a chance to conduct necropsies on 9 of the dead birds, and she found it interesting that there was no obvious determinate physical cause.  She conducted a gross necropsy, (which means looking at physical signs and what can be seen under a light microscope, but not histopathology, toxicology, or cultures) on 9 birds.  5 of the 9 were emaciated. Some had plastic in their digestive tract.  Other birds had squid beaks in their digestive tracts, which is a fairly common prey item, but since studies have shown that these can last for quite a while in their digestive tracts, they might not be indicative of their most recent feeding.  And one even had a fairly large quantity of sargassum.

Human Factors to Consider Include Plastic Pollution and Climate

Scientists seem to agree that climate plays some sort of factor, but are not exactly sure how.  Ocean currents may be warmer further north and support different prey species than the birds are used to.  Warmer summers may increase the “doldrum effect” in the middle of the ocean, making it harder for the birds to soar on the thermals where they want to go.

Plastic Ingestion by Great Shearwaters in the Atlantic Basin has been a documented issue for these birds for decades. Plastic fragments can be a cause of starvation if a bird has ingested them, creating blockages or reducing nutrients available to birds.

Macroplastics and Microplastics

Of the birds that Valerie necropsied that had plastic in them, much of the plastic was in the form of tiny pellets ~ pre-production plastic that gets melted down to make plastic items.  This is actually a big problem called by an inappropriately cute name: NURDLES. The primary microplastic looks a lot like natural prey in the marine ecosystem, but it comes with a heavy cost. The polymer composition allows biofilms and persistant organic pollutants that build up in seawater to attach to the nurdle, making them even more noxious.  Volunteers who handle large numbers of Nurdles are urged to wear gloves.  Here on Dewees Island, we are logging in our plastic trash that we find on the beach, and we seem to be far enough from the shipping terminals that we don’t see nurdles very often, but in 2019, there was a large nurdle spill that affected our local waters.  In fact, Charleston has been named the second-worst location in the nation for Nurdle pollution. Local environmental watchdog Charleston Waterkeeper is leading the discussion about the effects of this pollution, enlisting community scientists like me to document nurdle pollution on the beaches with their Nurdle Patrol project.

collected nurdles from our beach in 2019
nurdles and seaweed bits in the wrack line
This sargassum has tiny air bladders that are about the same size as nurdles

Every Bit of Clean-up Helps

Recently, the Dewees Island Conservancy hosted a happy hour and marsh clean-up.  Kelly Thorvalson, from the South Carolina Aquarium, gave us some great information on ocean plastics and sea turtles. The Aquarium has a great set of resources for communities and classrooms called their Plastic Toolkit. It’s a great set of resources for people who want to know how to help. Our turtle team logs our trash into the litter free digital journal, available for free from  App Store or Google Play.

Our island Sea Turtle Manual for Volunteers asks our walkers to log in garbage and shows examples of nurdles and how to report.

Not a Simple Answer

In the end, I am still not sure we have a perfectly neat explanation for all the causes for this mortality event.  If I learn more, I will update the post to reflect that.  I certainly enjoyed learning all about the shearwaters, and I love all the connections that weave through the community when we focus on protecting the nature we love.