Why Mudflats and Wading Birds Matter

In your many walks to Sand Dollar Island, I am sure you’ve seen stretches of muddy, murky, unvegetated habitat during low tide. But you won’t see them during high tide as they are submerged underwater. 

According to the World Atlas, “Mudflats refer to land near a water body that is regularly flooded by tides and is usually barren (without any vegetation). Also known as tidal flats, mudflats are formed upon the deposition of mud by tides or rivers. This coastal landform usually occurs in sheltered areas of the coast like bays, coves, lagoons, estuaries, etc. Since most of the sedimented area of a mudflat is within the intertidal zone, the mudflat experiences submersion under water and exposure twice daily.” 

This describes Sand Dollar Island and Tigertail Lagoon during low tide. The first thing walkers look for when coming upon the mudflat areas is the rich variety of birds feeding or resting. According to experts in tidal ecosystems, during high tide as the ocean water rises and floods the mudflats, they bring nutrients from the ocean. As the water recedes during low tide, it leaves behind nutrient-rich sediment, making the mudflat a hot spot for many marine organisms and especially birds!

According to FWC, Sand Dollar Island, also known as Big Marco Pass Critical Wildlife Area (CWA), “The submerged mudflats are posted year-round for the protection of migratory and residing foraging birds.”

I’ve seen many artists trying to capture the “beauty of the mudflats” at Tigertail Lagoon with the feeding birds in the background. The mudflats also attract birders and photographers patiently stalking a solitary long-neck white bird during low tide. 

An egret standing still or walking slowly, watching for movement in the water, is a common sight at the mudflats. Once they spot a prey in the water, they strike, grabbing the prey with its beak, their long legs and necks giving them that advantage. It never gets old, and for a local birder/photographer, this is the photo or memory of the day! 

Brittany Piersma, Audubon of the Western Everglades (AWE) biologist, has been surveying wading birds in the Tigertail Lagoon and Sand Dollar since 2019. “During the summer, I will survey twice a month and more in the winter months, and these surveys are all tide dependent, and birds are declining in general, but I noticed a major drop in numbers after the dredge project,” he shared.  “I decided to pull out numbers and aside from the Reddish Egret, we have been focusing on to see time-wise what changes occurred,” Piersma added. “The data I am collecting is to see what bird species adapt to changes better than others and to see how less shallow water and seagrasses after a dredge project affects their numbers. It was common amongst all birds to see greater numbers after breaches and erosion created shallow water in the lagoon. When the dredge project came back to modify the lagoon, the numbers drop again”

Piersma added, “Most alarming to me was the Great Egret. Great Egret numbers significantly dropped and stayed low. Snowy Egrets were similar. I used to have mornings of what I called “white Christmas” in the lagoon. Now I only see greater numbers during king tides or if storms crash sand into the lagoon to fill in the deep waters.”

“Tricolored Herons and Little Blue Herons seemed to be more resilient but still had drops after the project. White Ibis also dropped in number; Great Blue Herons, being the tallest, seem to be doing ok but definitely still value shallow water for feeding. Roseate Spoonbill were booming pre-dredge project. I was seeing them year-round. Post dredge project, they completely disappeared unless there is a mass king tide or erosion. A big reason would also be the seagrasses are almost entirely gone and covered in sand.”

Piersma also shared that “Mudflats, seagrasses, and mangroves have been dredged away and damaged by the Tigertail Dredging Project and could also be affecting the water quality and run-off continues directly into the lagoon and we are collecting deceased and sick birds year-round.”