Early in June, an assignment was given to write a “fun”and “light-hearted” article about dive-bombing Least Terns- the smallest of terns with their outsized aggressive behavior to protect their nests and chicks. This robin-sized white seabird with a black cap is often seen hovering over water and then diving straight down to catch baitfish. Once they nest, they use that same precision flying to harass anyone who comes near with loud squawks, and sometimes, poop!
Seabrook Island birder Ed Konrad has already detailed their unique courtship behavior of the male presenting a fish to his
prospective mate in earlier posts (“Spring on North Beach..”, April 26, 2019) and we were eagerly anticipating the arrival of this year’s crop of chicks.
But then it rained.
On May 28th, Janet Thibault, a coastal bird biologist for South Carolina Department of Natural Resources (SCDNR) had counted about 45 nesting pairs of “leasties” in the yellow sign posted, protected area at the eastern end of North Beach. This was very special news because after surveying the other known beach nesting sites in South Carolina, Seabrook’s North Beach was one of only a few where Least Terns had nested this year. The same area had 53 nesting pairs last year (2018) which was the first successful nesting (chicks produced) since the new cut at Captain Sams was made in 2015. Other attempts to nest had failed because Least Terns are colony nesters and a predatory threat, like the pair of coyotes that were reported on the beach during one of those summers, can send the whole flock packing.
Almost anything you read about Least Terns mentions their inability to find safe places to nest. Instead, they use vulnerable or precarious places like sandbars prone to over wash on a king tide or gravel covered roof tops like those of big box stores in Mount Pleasant! In fact, with the loss of suitable beach habitat, over 60% of Least Tern nests in South Carolina are on roof tops with SCDNR monitoring those in a special program. Habitat loss and disturbances like predators and human use of beaches are the reasons behind Least Terns being classified as Threatened in South Carolina.
Eggs are laid in a shallow scrape starting in mid-May and are incubated for 19-25 days. After the chicks hatch, the parents hide them in the shade which can be something as meager as a pile of spartina grass wrack on the beach. For this reason, beach walkers and those in vehicles need to be careful to watch for the chicks and avoid walking or driving on debris or piles of wrack. The young terns fly in about another 20 -25 days. All told, the nesting site needs to provide a stable and safe shelter for almost two months.
In comparison to sandbars and roof tops, the yellow-sign protected area on North Beach with its large dry sand beach or the top of the dike with its shell-mash surface appears to be very secure. The Least Terns here nested mainly in the middle of the protected area in slight depressions surrounded by low dunes to protect them from the wind. The nests were fairly close together and when a gull or crow flew too close, small flocks of terns would rise up out of the sand to intercept the intruder. Those depressions were also the areas that may have filled with rain water and ended Least Tern nesting for this year.
For much of May, we had unusually dry weather, but the weekend, June 6 -10th, saw heavy rain with some significant downpours. It is hard to imagine flooding on a sand beach, but in early June, we had a series of very high tides with the resulting wrack line reaching well inside the line of posting signs. By the morning of June 10th, water was ponding in the area where the old “Cat Eye” pond used to be. My notes from early on
June 10th say that I saw fewer nesting terns and less overall activity compared to my observations from the week before. Later that same morning another storm produced 0.6” of rain in 20 minutes.
On Wednesday June 12th, I was caught in a rain squall just after sunrise. The nesting birds that had been in the central depression were gone. A few Least Terns were sheltering under the dead spartina grass of the higher wrack and some, only 33 birds over 35 minutes, would occasionally lift up from behind low dunes and fly to better protection in the vegetation. Streams were flowing out from the old Cat Eye pond area and through the posted area to the tidal lagoon. Puddles were forming in the lower areas of the protected area.The weather data from a nearby weather station on Seabrook shows a total of 2.85” over 3 hours. Downtown Charleston flooded with nearly
four inches of rain.
The next morning, the protected area was unusually quiet. I counted only nine Least Terns where once there were more than one hundred: one bird was still nesting, one was foraging and the others were counted as they flew in the back dunes. The wrack where I had seen birds sheltering the morning before was buried in sand. Water still lay in the area of the old Cat Eye pond. The central depressions were wet but did not hold standing water.
Janet Thibault came back on the 14th and we walked the area. We only saw 2 Least Terns and they were feeding over the lagoon. The last nesting bird was gone. Janet said that we should watch to see if they attempt to re-nest, but that, she said, was unlikely this late in the season.
North Beach offered seemingly perfect habitat but nature can be cruel. With Least Tern numbers down over 80% from the mid-1960‘s, we have unfortunately seen first hand how fragile Least Tern nesting can be even in the best of circumstances.
Janet and I continued our walk behind the dike and found a pair of Wilson’s Plovers, also Threatened. We watched for quite awhile but didn’t see any chicks; they do a great job of hiding them in the vegetation. Earlier in the week, two Wilson’s Plover chicks that were born to parents outside the protected area were seen near the last dog sign. They are probably still hidden in the dunes – hopefully out of the reach of the storms.
Submitted by: Mark Andrews