Study could help reveal effects of red tide
A study on reddish egrets at the J.N. “Ding” Darling National Wildlife Refuge that involves satellite tracking and fish sampling was recently expanded to try and determine what effects toxins like red tide may be having on the birds and perhaps other species.
Supported by funding from the “Ding” Darling Wildlife Society-Friends of the Refuge, the Avian Research and Conservation Institute in Gainesville has been partnering with refuge since 2016 to study the birds. ARCI Executive Director Ken Meyer explained that three of them were tagged with satellite tracking, along with two found at Bunche Beach, in addition to samples being taken of their prey.
Eight birds in the Florida Keys were also tagged.
The aim is to study their movements and survival and identify how much habitat they require.
“This is the single species of wading bird in Florida that is of the most concern because it’s population is very small and appears to be declining,” he said.
Noting that the refuge supports a small but consistent breeding population of no more than 10 or so reddish egrets, Meyer explained that there is no such thing in the United States as “medium” or “large” populations. From Tampa to the Keys, the total Florida breeding population is likely under 350 pairs.
“There’s probably about 15 hot spots in the whole state,” he said of nesting locations.
In addition to tracking the birds, the team focused on where the tagged ones were catching fish at the refuge and on Bunche Beach. They sampled their prey in the winter of 2016 and summer of 2017.
“We sampled the fish systemically using the throw net where the reddish egrets were feeding,” Meyer said. “Our curiosity was what species of fish and what size fish are available to the reddish egret.”
The work all took place prior to the start of the initial red tide event from October 2017.
“I originally asked Ken to include the fish sampling as part of his research to provide some baseline data on the prey the reddish egrets were targeting,” Refuge Manager Paul Tritaik said.
In examining the movements of the tagged birds over this past summer, as small and large marine life washed ashore dead from red tide, they discovered that one had flown to the Ten Thousand Islands.
“It was the first time this individual has left the area around Sanibel and Pine Island and Bunche Beach,” he said. “So I thought that was interesting that it coincided with the red tide event.”
Tritaik explained that he asked Meyer and his team if they could repeat the sampling.
“To see what prey availability there was and see if that was potentially a factor in the bird’s movement – to compare what the condition of the fishery was that the birds were feeding on as a result of the red tide,” he said. “I thought it could provide a good model for what was happening with other species.”
Meyer explained that the sampling was conducted in late October-early November, after the refuge experienced a year-long red tide event that appeared to be subsiding. The sites where the sampling took place were the same as in the first project – one area on Bunche Beach and one off Wildlife Drive.
“We used exactly the same methods in every regard, including where the reddish egrets were forging,” he said, adding that a second sampling will be taken in a couple months to mirror the first project.
Meyer pointed out that the samples collected at the refuge were taken from the water on both sides, so the impounded areas managed by the refuge and the open waters between Sanibel and Pine Island.
“The water coming out of the Caloosahatchee,” he said.
While the parameters of the study remain the same, the second project was expanded.
“We collected a sample of fish to measure two toxins,” Meyer said.
The new samplings will look at mercury content, which is common in Florida waterways for fish and fish-eating species, and brevetoxin, which is the neurotoxin that affects animals exposed to red tide.
Fish sampling for toxins has been done, but not sampling the same sites used as a food source.
“This is the first time that this sort of pre-sampling and contaminant sampling has been attempted,” he said. “We hope to get a sense of how much these toxins put the reddish egrets at risk.”
Tritaik added to that.
“The birds that he’s tracking provide real-time data on their movements, so it’ll be interesting to see if there’ll be any other changes in the birds’ movements related to the conditions here at the refuge,” he said. “I think it’s particularly important because the red tide conditions are still going on and we don’t know for how long.”
The results of the study will not be available until next year.
“There are some apparent differences with the first project, but it’s too early to tell if they’re meaningful,” Meyer said.
He did share one interesting “clear result” from the first project and first sampling of the second project. Meyer explained that the refuge birds and Bunche Beach birds are preying on very different fish populations. The reddish egrets at Bunche are eating larger fish, but the quantity is smaller.
“The two birds over there have their own defined hunting areas and they appear to be very competitive,” he said.
At the refuge, the fish are smaller in size but there is a larger number of them. Meyer noted that the three reddish egrets are less competitive toward each other and their hunting areas even overlap.
Both men credited the DDWS for enabling the study to take place.
“If it wasn’t for the Wildlife Society, we wouldn’t be doing this,” Meyer said, noting that the refuge provides support also. “The ‘Ding’ Darling National Wildlife Refuge is absolutely one of the best places for us to be doing this research – they are very interested in applying our results to management.”
“Without their support, we wouldn’t have been able to have Ken conduct the study at the refuge,” Tritaik said. “It underscores the value of what the ‘Ding’ Darling Wildlife Society does for the refuge.”
DDWS also supports educational and visitor services-related programs.
“But they also are vital to supporting some of the very basic needs of the refuge in terms of biological research,” he said.
DDWS Executive Director Birgie Miller noted that donor gifts make the support possible.
“Without the science, it’s difficult to have the right answers on managing the refuge and the refuge wildlife,” she said. “We help the refuge with programs and research and anything that they need to do the conservation work at the refuge that they cannot get the funding for – to fill in those gaps.”
“It takes everybody working together,” Miller added.
To donate, contact Miller at 239-472-1100 ext. 4 or director@dingdarlingsociety.com.