When a sparrow’s nest flooded the coast of Georgia during high tide, a fish seized the opportunity to cook a meal from a newly hatched chick, and a scientist’s video camera caught a glimpse of the entire deadly encounter for the first time.
The images showed a small fish called a mummichog (Fundulus heteroclitus) jumping into a flooded nest and attacking a young sparrow by the sea (Ammospiza maritima), showing that baby sparrows in this habitat face a threat previously unknown to scientists.
Corina Newsome, an ornithologist at the Hunter Lab at Georgia Southern University in Statesboro, had placed cameras on the bird’s nests to learn about the risks posed by predators. In this case, the predator came from an unexpected place: the water.
“When I saw that, a lot of questions were spinning in my head,” Newsome told Live Science.
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Tidal salt marshes in Georgia are home to many species of birds, and sea sparrows that live there are known to build their nests in areas prone to flooding when the tide rises, Newsome and her co-authors reported Feb. 5 in The Wilson Journal of OrnithologyThis can be dangerous for young chicks, although they often survive minor floods, according to the study.
But choosing a drier nesting site that is higher up may expose the fry more to a number of predators, Newsome said. Larger birds such as crows or grackles love baby sparrows, as do raccoons, rice rats and American mink; and sparrow chicks are generally safer in nests closer to the ground as this gives them a protective cover.
Salt marshes are also inhabited by the hardy mummichog. These fish are up to 3 inches (9 centimeters) long, are very tolerant of adverse conditions, such as low oxygen levels and dramatic temperature changes, and they feast on a variety of small aquatic animals, including snails, mussels and other fish, the researchers wrote. the study.
A threat from below
On June 5, 2019, one of Newsome’s cameras recorded an unusual activity in a flooded sparrow’s nest during high tide. The nest contained two eggs and a chick that hatched earlier that day.
“In the video you can see how the water gradually rises in the nest and the chick floats on top of the water,” said Newsome. Suddenly a fish jumps over the edge of the nest, rests next to the floating chick – and then it strikes. The mummichog pulled the chick under water and “punched the chick in its mouth” until the nestling drowned, the study said.
A flooded nest isn’t necessarily an automatic death sentence for baby sparrows – if they can keep their heads above water and the water drops before their body temperature drops too much, even a newly hatched baby bird can survive a dunking.
“But having predators accessing the nest with the water poses a whole new threat,” Newsome said. Nothing like this had previously been reported by scientists, she added.
The encounter may have filled the mummichog’s belly, but it left the researchers hungry for answers about this previously invisible danger. For example, Newsome asked, how does nest predation threat differ between aquatic and terrestrial predators? Do sparrows build their nests to optimize their protection against one type of predator and then become more vulnerable to others? And are fish the only aquatic carnivores to benefit from flooded nests, or do terrapins snack on young at high tide?
“There has been a lot of research to show that nest predation increases as the height of the nest above the ground increases,” explains Newsome. “But this adds a complication to what predation threats actually look like to this species.”
Originally published on Live Science.