Scientists at work: Sloshing through marshes to see how birds survive hurricanes

A clapper rail with a fiddler crab in its bill.
Michael Gray, CC BY-ND

Scott Rush, Mississippi State University and Mark Woodrey, Mississippi State University

When storms like Huricane Zeta menace the Gulf Coast, residents know the drill: Board up windows, clear storm drains, gas up the car and stock up on water, batteries and canned goods.

But how does wildlife ride out a hurricane? Animals that live along coastlines have evolved to deal with a world where conditions can change radically. This year, however, the places they inhabit have borne the brunt of 10 named storms, some just a few weeks apart.

As wildlife ecologists, we are interested in how species respond to stresses in their environment. We are currently studying how marsh birds such as clapper rails (Rallus crepitans) have adapted to tropical storms along the Alabama and Mississippi Gulf coast. Understanding how they do this entails wading into marshes and thinking like a small, secretive bird.

A least bittern, one of the smallest species of heron.
Michael Gray, CC BY-ND

Mucky and full of life

Coastal wetlands are critically important ecosystems. They harbor fish, shellfish and wading birds, filter water as it flows through and buffer coastlines against flooding.

You wouldn’t choose a Gulf Coast salt marsh for a casual stroll. There are sharp-pointed plants, such as black needlerush​, and sucking mud. In summer and early fall the marshes are oppressively hot and humid. Bacteria and fungi in the mud break down dead material, generating sulfurous-smelling gases. But once you get used to the conditions, you realize how productive these places are, with a myriad of organisms moving about.

Marsh birds are adept at hiding in dense grasses, so it’s more common to hear them than to see them. That’s why we use a process known as a callback survey to monitor for them.

First we play a prerecorded set of calls to elicit responses from birds in the marsh. Then we determine where we think the birds are calling from and visually estimate the distance from the observer to that spot, often using tools such as laser range finders. We also note the type of ecosystem where we detect the birds – for example, whether they’re in a tidal marsh with emergent vegetation or out in the open on mud flats.

Adult clapper rail calling.

Through this process we’ve been able to estimate the distributions of several species in tidal marshes, including clapper rails, least bitterns (Ixobrychus exilis) and seaside sparrows (Ammospiza maritima). We’ve also plotted trends in their abundance and identified how their numbers can change with characteristics of the marsh.

We’ve walked hundreds of miles through marshes to locate nests and to record data such as nest height, density of surrounding vegetation and proximity to standing water, which provides increased foraging opportunities for rails. Then we revisit the nests to document whether they produce young that hatch and eventually leave. Success isn’t guaranteed: Predators may eat the eggs, or flooding could wash them out of the nest and kill the developing embryos inside.

Salt marshes shelter many types of plants, birds, animals, fish and shellfish.

Rails in the grass

Our research currently focuses on clapper rails, which look like slender chickens with grayish-brown feathers and short tails. Like many other marsh birds, they have longish legs and toes for walking across soft mud, and long bills for probing the marsh surface in search of food. They are found year-round along the Atlantic and Gulf coasts.

Clapper rails typically live in tidal marshes where there is vegetation to hide in and plenty of fiddler crabs, among their frequent foods. Because they are generally common and rely on coastal marshes, they are a good indicator of the health of these coastal areas.

Ecologist Scott Rush with clapper rail, Pascagoula River Marshes, Mississippi.
Mark Woodrey, CC BY-ND

Water levels in tidal marshes change daily, and clapper rails have some adaptations that help them thrive there. They often build nests in areas with particularly tall vegetation to hide them from predators. And they can raise the height of the nest bowl to protect it against flooding during extra-high or “king” tides and storms. The embryos inside their eggs can survive even if the eggs are submerged for several hours.

When a tropical storm strikes, many factors – including wind speed, flooding and the storm’s position – influence how severely it will affect marsh birds. Typically birds ride out storms by moving to higher areas of the marsh. However, if a storm generates extensive flooding, birds in affected areas may swim or be blown to other locations. We saw this in early June when Hurricane Cristobal blew hundreds of clapper rails onto beaches in parts of coastal Mississippi.

Clapper rails on a Mississippi beach after Hurricane Cristobal in June 2020.
Mark Woodrey, CC BY-ND

In coastal areas immediately to the east of the eye of a tropical cyclone we typically see a drop in clapper rail populations in the following spring and summer. This happens because the counterclockwise rotation of the storms results in the highest winds and storm surge to the north and east of the eye of the storm.

But typically there’s a strong bout of breeding and a population rebound within a year or so – evidence that these birds are quick to adapt. After Hurricane Katrina devastated the Mississippi Gulf Coast in 2005, however, depending on the type of marsh, it took several years for rail populations to return to their pre-Katrina levels.

Now we’re radio-tagging clapper rails and collecting data that allow us to determine the birds’ life spans. This information helps us estimate when large numbers of birds have died – information that we can correlate with events like coastal hurricanes.

Summary map of the 2020 Atlantic hurricane season, updated Oct. 27.
Master0Garfield/Wikipedia

Losing parts

Tropical storms have shaped coastal ecosystems since long before recorded history. But over the past 150 years humans have complicated the picture. Coastal development – draining marshes, building roads and reinforcing shorelines – is altering natural places that support marsh birds.

Clapper rails and other species have evolved traits that help them offset population losses due to natural disasters. But they can do so only if the ecosystems where they live keep providing them with food, breeding habitat and protection from predators. Coastal development, in combination with rising sea levels and larger tropical storms, can act like a one-two punch, making it increasingly hard for marshes and the species that live in them to recover.

[Deep knowledge, daily. Sign up for The Conversation’s newsletter.]

Biologist Paul Ehrlich has compared species at risk to rivets on an airplane. You might not need every rivet in place for the airplane to fly, but would you fly it through a cyclone if you knew that 10% of its rivets were missing? What about 20%, or 30%? At some point, Ehrlich asserts, nature could lose so many species that it becomes unable to provide valuable services that humans take for granted.

We see coastal marshes as an airplane that humans are piloting through storms. As species and ecosystem services are pummeled, rivets are failing. No one knows where or how the aircraft will land. But we believe that preserving marshes instead of weakening them can improve the chance of a smooth landing.

Scott Rush, Assistant Professor of Wildlife Ecology and Management, Mississippi State University and Mark Woodrey, Assistant Research Professor, Mississippi State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Advertisement

Where’s the sea ice? 3 reasons the Arctic freeze is unseasonably late and why it matters

Arctic sea ice levels have been falling for several decades.
GraphicaArtis/Getty Images

Mark Serreze, University of Colorado Boulder

With the setting of the sun and the onset of polar darkness, the Arctic Ocean would normally be crusted with sea ice along the Siberian coast by now. But this year, the water is still open.

I’ve watched the region’s transformations since the 1980s as an Arctic climate scientist and, since 2008, as director of the National Snow and Ice Data Center. I can tell you, this is not normal. There’s so much more heat in the ocean now than there used to be that the pattern of autumn ice growth has been completely disrupted.

To understand what’s happening to the sea ice this year and why it’s a problem, let’s look back at the summer and into the Arctic Ocean itself.

Siberia’s 100-degree summer

The summer melt season in the Arctic started early. A Siberian heat wave in June pushed air temperatures over 100 degrees Fahrenheit at Verkhoyansk, Russia, for the first time on record, and unusual heat extended over much of the Arctic for weeks.

The Arctic as a whole this past summer was at its warmest since at least 1979, when satellite measurements started providing data allowing for full coverage of the Arctic.

With that heat, large areas of sea ice melted out early, and that melting launched a feedback process: The loss of reflective sea ice exposed dark open ocean, which readily absorbs the sun’s heat, promoting even more ice melt.

The Northern Sea Route, along the Russian coast, was essentially free of ice by the middle of July. That may be a dream for shipping interests, but it’s bad news for the rest of the planet.

Warmth sneaks in underwater

The warm summer is only part of the explanation for this year’s unusual sea ice levels.

Streams of warmer water from the Atlantic Ocean flow into the Arctic at the Barents Sea. This warmer, saltier Atlantic water is usually fairly deep under the more buoyant Arctic water at the surface. Lately, however, the Atlantic water has been creeping up. That heat in the Atlantic water is helping to keep ice from forming and melting existing sea ice from below.

It’s a process called “Atlantification”. The ice is now getting hit both from the top by a warming atmosphere and at the bottom by a warming ocean. It’s a real double whammy.

While we’re still trying to catch up with all of the processes leading to Atlantification, it’s here and it’s likely to get stronger.

Climate change’s assault on sea ice

In the background of all of this is global climate change.

The Arctic sea ice extent and thickness have been dropping for decades as global temperatures rise. This year, when the ice reached its minimum extent in September, it was the second lowest on record, just behind that of 2012.

As the Arctic loses ice and the ocean absorbs more solar radiation, global warming is amplified. That can affect ocean circulation, weather patterns and Arctic ecosystems spanning the food chain, from phytoplankton all the way to top predators.

On the Atlantic side of the Arctic, open water this year extended to within 5 degrees of the North Pole. The new Russian Icebreaker Arktika, on its maiden voyage, found easy sailing all the way to the North Pole. A goal of its voyage was to test how the nuclear-powered ship handled thick ice, but instead of the hoped-for 3-meter-thick ice, most of the ice was in a loose pack. It was little more than 1 meter thick, offering little resistance.

For sea ice to build up again this year, the upper layer of the Arctic Ocean needs to lose the excess heat it picked up during summer.

The pattern of regional anomalies in ice extent is different each year, reflecting influences like regional patterns of temperature and winds. But today, it’s superimposed on the overall thinning of the ice as global temperatures rise. Had the same atmospheric patterns driving this year’s big ice loss off Siberia happened 30 years ago, the impact would have been much less, as the ice was more resilient then and could have taken a punch. Now it can’t.

Is sea ice headed for a tipping point?

The decay of the Arctic sea ice cover shows no sign of stopping. There probably won’t be a clear tipping point for the sea ice, though.

Research so far suggests we’ll stay on the current path, with the amount of ice declining and weather systems more easily disrupting the ice because it’s thinner and weaker than it used to be.

The bigger picture

This year’s events in the Arctic are just part of the climate change story of 2020.

Global average temperatures have been at or near record highs since January. The West has been both hot and dry – the perfect recipe for massive wildfires – and warm water in the Gulf of Mexico has helped fuel more tropical storms in the Atlantic than there are letters in the alphabet. If you’ve been ignoring climate change and hoping that it will just go away, now would be an appropriate time to pay attention.

Mark Serreze, Research Professor of Geography and Director, National Snow and Ice Data Center, University of Colorado Boulder

This article is republished from The Conversation under a Creative Commons license. Read the original article.